Factibilidad de la bipartición hepática derecha-izquierda in situ en el trasplante Hepático / Feasibility of in situ full-right full-left split liver transplantation

Debido a la falta de órganos para trasplantes se han desarrollado diferentes alternativas quirúrgicas, como la bipartición hepática (BH) y los trasplantes hepáticos con donantes vivos. En la BH clásica, de la división de un hígado de donante cadavérico se obtienen dos injertos, uno correspondiente a los segmentos 2-3 y otro a los segmentos 1, 4-8. Para poder utilizar los injertos de una BH, en pacientes adultos, se puede realizar una BH derecha/izquierda típica, donde se obtienen un injerto derecho (segmentos 5-8) y otro izquierdo (segmentos 1-4). La BH se puede realizar en el momento de la ablación (BH in situ) o en la cirugía de banco (BH ex situ). En este trabajo informamos el primer caso de BH in situ derecha/izquierda típica de la Argentina, resaltando los detalles de la cirugía del donante y del receptor.

Due to the shortage of organs for transplantation, different surgical alternatives have been developed, as split liver transplantation (SLT) and living-donor liver transplantation. In classical SLT, the liver of a cadaveric donor is divided and two allografts are obtained, one corresponding to segments 2-3 and the other to segments 1, 4-8. In order to produce two grafts from one liver for two adult recipients, splitting of the liver can create a right graft including segments 5-8 and a left graft with segments 1-4. Splitting of the liver can be performed during procurement (in situ) or on the bench (ex situ). The aim of our study is to describe the first case of in situ full-right full-left split liver transplantation, with focus on donor and recipient surgery.

Coronary reactive hyperaemia and arterial pressure in anaesthetized goats.

To study the effects of arterial pressure on coronary reactive hyperaemia, left circumflex coronary artery flow was measured, and reactive hyperaemia was determined after 5, 10 or 20 s of occlusion of this artery in anaesthetized goats during normotension, hypertension and hypotension. During hypertension induced by aortic constriction (mean arterial pressure, MAP = 140 +/- 6 mmHg) coronary vascular resistance (CVR), reactive hyperaemia (ratio of peak in hyperaemic flow to control flow and ratio of repayment to debt) and the decrease in CVR during the peak in hyperaemic flow were comparable to those during normotension. During hypertension induced by noradrenaline (MAP = 144 +/- 6 mmHg) CVR was 16% lower (P < 0.05), reactive hyperaemia was reduced by 14-25% (P < 0.05) and the decrease in CVR during the peak in hyperaemic flow was lower than the values of these parameters during normotension. During hypotension induced by constriction of the caudal vena cava (MAP = 40 +/- 4 mmHg) CVR was 22% lower (P < 0.05), reactive hyperaemia was reduced by 25-65% (P < 0.05) and the decrease in CVR during the peak in hyperaemic flow was less compared to the values of these parameters during normotension. During hypotension induced by isoprenaline (MAP = 45 +/- 4 mmHg) CVR was 59% lower, reactive hyperaemia was reduced by 55-100% (P < 0.01) and the decrease in CVR during the peak in hyperaemic flow was less compared to the values of these parameters during normotension. Arterial pressure is a main determinant of coronary reactive hyperaemia after brief periods of ischaemia, and the relationship between arterial pressure and reactive hyperaemia may depend in part on changes in CVR after variations in arterial pressure. These changes in CVR may be related to the action on coronary vessels of myocardial factors and vascular myogenic mechanisms.

Diabetes abolishes the gender difference in vasopressin-mediated potentiation of sympathetic vasoconstriction.

Electrical field stimulation (4 Hz, 0.2 ms pulse duration, at a supramaximal voltage of 70 V, for 1 s) of isolated rat tail artery segments produced contraction which was lower in female than in male rats, and was reduced by streptozotocin-induced diabetes in both genders. This contraction was potentiated by vasopressin (10(-12)-10(-10) M) more in normoglycemic male than in normoglycemic female rats, and this effect of vasopressin was increased by the cyclooxigenase inhibitor meclofenamate (10(-5) M) in female control rats, but not in diabetic female, or control and diabetic male rats, and it was not modified by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 10(-4) M). Endothelin-1 (10(-10)-3 x 10(-9) M) also potentiated the contraction to electrical stimulation. This potentiation was similar in all experimental groups, and it was not modified by meclofenamate or L-NAME. These results suggest that the potentiating effect of vasopressin, but not that of endothelin-1, on the sympathetic vasoconstriction, is lower in females than in males, probably by an increased release of vasodilating prostanoids, and this release may be reduced by diabetes in females.

Adrenergic vasoconstrictor activity in the cerebral circulation after inhibition of nitric oxide synthesis in conscious goats.

The interaction between nitric oxide (NO) and adrenergic activity in the cerebral circulation was studied using conscious goats, where blood flow to one brain hemisphere (cerebral blood flow) was electromagnetically measured, and the effects of phentolamine and hexamethonium on cerebrovascular resistance were evaluated before (control) and after inhibition of NO synthesis with NW-nitro-L-arginine methyl ester (L-NAME). L-NAME (12 goats, 40 mg kg(-1) administered i.v.) reduced cerebral blood flow from 62 +/- 3 to 44 +/- 2 ml min(-1), increased mean systemic arterial pressure from 100 +/- 3 to 126 +/- 4 mm Hg, decreased heart rate from 79 +/- 5 to 50 +/- 4 beats min(-1) and increased cerebrovascular resistance from 1.63 +/- 0.08 to 2.91 +/- 0.016 mm Hg ml(-1)min(-1) (all P < 0.01). These hemodynamic variables normalized 48-72 h after L-NAME administration. Phentolamine (six goats, 1 mg), injected into the cerebral circulation. increased cerebral blood flow without changing systenic arterial pressure, but its cerebrovascular effects were augmented for about 24 h after L-NAME. The decrements in cerebrovascular resistance induced by phentolamine, in mm Hg ml(-1) min(-1), were: under control, 0.42 +/- 0.05; immediately after L-NAME, 1.38 +/- 0.09 (P < 0.01 compared with control); by about 24 h after L-NAME, 0.71 +/- 0.09 (P < 0.05 compared with control); and by about 48 h after L-NAME, 0.40 +/- 0.07 (P > 0.05 compared with control). Hexamethonium (six goats, 0.5-1 mg kg(-1) min(-1) i.v.) decreased mean systemic arterial pressure to about 75 mm Hg and caused tachycardia similarly before and after L-NAME, but the decrements in cerebrovascular resistance were augmented for about 24 h after L-NAME. The decrements in cerebrovascular resistance induced by hexamethonium, in mm Hg ml(-1).min(-1), were: under control. 0.61 +/- 0.09, immediately after L-NAME, 1.33 +/- 0.16 (P < 0.01 compared with control); by about 24 h after L-NAME, 1.18 +/- 0.10 (P < 0.01 compared with control): and by about 48 h after L-NAME, 0.99 +/- 0.10 (P > 0.05 compared with control). Therefore, these results suggest that adrenergic vasoconstrictor tone in cerebral vasculature may be augmented after inhibition of NO synthesis, and that this increment may contribute to the reduction of cerebral blood flow after inhibition of NO formation.

Cerebral vasoconstriction produced by vasopressin in conscious goats: role of vasopressin V(1) and V(2) receptors and nitric oxide.

To examine the role of vasopressin V(1) and V(2) receptors, nitric oxide and prostanoids in the cerebrovascular effects of arginine vasopressin, cerebral blood flow was electromagnetically measured in awake goats. In 16 animals, vasopressin (0.03 - 1 microg), injected into the cerebral circulation, caused increments of resting cerebrovascular resistance which ranged from 18% (0.03 microg, P<0.01) to 79% (1 microg, P<0.01). Desmopressin (0.03 - 1 microg, four goats) did not affect significantly cerebrovascular resistance. The cerebrovascular resistance increases by vasopressin were reduced significantly by the antagonist for vasopressin V(1) receptors d(CH(2))(5)Tyr(Me)-AVP in a rate depending way (five (six goats) and 15 (four goats) microg min(-1)), and by the mixed antagonist for vasopressin V(1) and V(2) receptors desGly-d(CH(2))(5)-D-Tyr(Et)Val-AVP (5 microg min(-1), four goats), and they were not significantly affected by the antagonist for vasopressin V(2) receptors d(CH(2))(5), D-Ile(2), Ile(4)-AVP (5 microg min(-1), four goats). The inhibitor of nitric oxide synthesis N(w)-nitro-L-arginine methyl ester (L-NAME, 47 mg kg(-1) i.v., five goats) augmented cerebrovascular resistance by 130% (P<0.01), and for 24 h after this treatment the cerebrovascular effects of vasopressin were potentiated. The inhibitor of cyclo-oxygenase meclofenamate (6 mg kg(-1) i.v., five goats) did not modify significantly resting haemodynamic variables measured or the cerebrovascular effects of vasopressin. Therefore, the vasopressin-induced cerebral vasoconstriction may be mediated by vasopressin V(1) receptors, without involvement of vasopressin V(2) receptors, and may be modulated by nitric oxide but not by prostanoids.

Effect of neuropeptide Y on the sympathetic contraction of the rabbit central ear artery during cooling.

In order to analyse the effect of neuropeptide Y (NPY) on the cutaneous vascular response to sympathetic nerve stimulation during cooling, the isometric response of isolated 2-mm segments of the rabbit central ear (cutaneous) artery was recorded at 37 degrees C and during cooling (30 degrees C). Electrical field stimulation (4-16 Hz) at 37 degrees C produced a frequency-dependent contraction, which was reduced during cooling (45% for 16 Hz) and potentiated by NPY (10(-8), 3x10(-8) and 10(-7) M), this potentiation being greater at 30 degrees C than at 37 degrees C. The NPY-induced potentiation of the contraction elicited by electrical field stimulation (8 Hz) was abolished by an antagonist of Y1 subtype NPY receptors, BIBP3226 (10(-6) M), at 37 degrees C and 30 degrees C, reduced by phentolamine (10(-6) M) at 30 degrees C but not at 37 degrees C, was not modified by the purinoceptor antagonist PPADS (3x10(-5) M) and was reduced by application of both phentolamine and PPADS at both temperatures. Both NiCl2 (10(-3) M) and verapamil (10(-5) M) abolished the potentiating effect of NPY at 37 degrees C and reduced it at 30 degrees C. Neither application of an inhibitor of nitric oxide synthesis, L-Nomega-nitro-arginine (L-NOARG, 10(-4) M), nor endothelium removal modified the potentiating effect of NPY at 37 degrees C or 30 degrees C. NPY (10(-8), 3x10(-8) and 10(-7) M) potentiated in a concentration-dependent way the arterial contraction in response to exogenous noradrenaline (10(-8)-10(-4) M) at 30 degrees C but not at 37 degrees C, and it increased the response to ATP (10(-4)-10(-2) M) at both temperatures. Therefore, in cutaneous (ear) arteries: (1) NPY potentiates the sympathetic response at 37 degrees C and at 30 degrees C, (2) this potentiating effect of NPY was more marked at 30 degrees C than at 37 degrees C, probably because of greater potentiation of the alpha-adrenoceptor response during cooling, and (3) the potentiating effect of NPY at both temperatures is mediated by NPY receptors of the Y1 subtype, is dependent of Ca2+ channels and is independent of the release of endothelial nitric oxide.

Impaired potentiation by endothelin-1 and vasopressin of sympathetic contraction in tail artery from hypertensive rats.

OBJECTIVE: To analyse the effects of endothelin-1 and vasopressin on the sympathetic vasoconstriction during hypertension. METHODS: Electrical field stimulation (4 Hz) was applied to isolated, 2 mm segments of the tail artery from spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats prepared for isometric tension recording. RESULTS: The contraction to electrical stimulation was potentiated by endothelin-1 (10(-10)-10(-8) M) in arteries from WKY but not from SHR, and by vasopressin (10(-12)-10(-10) M) more markedly in arteries from WKY than from SHR. The potentiation by endothelin-1 was reduced more markedly by the antagonist of endothelin ETA receptors BQ-123 (10(-5) M) than by the endothelin ETB receptor antagonist BQ-788 (10(-5) M). The potentiation by vasopressin was reduced by the antagonist of vasopressin V1 receptors d(CH2)5Tyr(Me)AVP (10(-7) M), but not by the vasopressin V2 receptor antagonist d(CH2)5D-Ile2, Ile4AVP (10(-7) M). The blocker of L-type calcium channels verapamil (10(-5) M) reduced the potentiation by both endothelin-1 and vasopressin in arteries from WKY rats, and increased the potentiation by vasopressin in arteries from SHR. Noradrenaline (10(-8)-10(-4) M) contraction was not modified by endothelin-1 (3 x 10(-9) M) or vasopressin (3 x 10(-11) M), and contraction to endothelin-1 (10(-9)-10(-7) M) and vasopressin (10(-10)-10(-7) M) was lower in arteries from SHR than from WKY rats. CONCLUSIONS: (1) The potentiation by endothelin-1 and vasopressin of the sympathetic vasoconstriction, probably due to increased release of noradrenaline, is impaired during hypertension, and (2) this potentiation is mediated mainly by endothelin ETA receptors, and by vasopressin V1 receptors, in both WKY and SHR, and for both peptides it is mediated by L-type calcium channels in arteries from normotensive but not in those from hypertensive animals.

Role of nitric oxide in vascular tone and in reactivity to isoproterenol and adenosine in the goat coronary circulation.

The present study examined the role of nitric oxide in coronary vascular tone and in the coronary vasodilatation in response to beta-adrenoceptor stimulation and adenosine. In anesthetized goats, the effects of intracoronary and i.v. administration of the inhibitor of nitric oxide synthesis, N(w)-nitro-L-arginine methyl ester (L-NAME), and those of isoproterenol, adenosine and acetylcholine on coronary blood flow, measured electromagnetically in the left circumflex coronary artery, were recorded. Intracoronary infusion of L-NAME (30-40 microg kg(-1) min(-1), four goats) reduced resting coronary blood flow by 14+/-3% (P<0.05) without changing arterial pressure and heart rate. L-NAME (40 mg kg(-1), eight goats) i.v. reduced resting coronary blood flow by 19+/-4% (P<0.05), increased mean systemic arterial pressure by 22+/-3% (P<0.01) and decreased heart rate by 10+/-2% (P<0.05). These effects of L-NAME were partially, but significantly reversed by L-arginine (six goats). Isoproterenol (10-100 ng, eight goats), adenosine (0.3-10 microg, seven goats) and acetylcholine (3-100 ng, five goats), injected intracoronarily, increased coronary conductance in a dose-dependent way and, under control conditions, these increases for isoproterenol, ranged from 32+/-5% to 82+/-12%; for adenosine, 6+/-2% to 174+/-22%; and for acetylcholine, 39+/-5% to 145+/-15%. During i.v. L-NAME the increases in coronary conductance induced by isoproterenol and acetylcholine were significantly reduced by about 50 and 60% (P<0.05), respectively, whereas those induced by adenosine were significantly increased further (about 30-100%, P<0. 05). During L-NAME plus L-arginine, the effects of isoproterenol, acetylcholine and adenosine on coronary conductance were not significantly different from those under control conditions. Therefore, it is suggested that in the coronary circulation: (a) nitric oxide may produce a basal vasodilator tone under normal conditions; (b) nitric oxide may be an intermediate in the vasodilatation due to beta-adrenoceptor stimulation and acetylcholine, and (c) the vasodilatation due to adenosine is potentiated during reduction of nitric oxide production.

Insulin effects on the sympathetic contraction of rabbit ear arteries.

Electrical field stimulation (4 Hz, 0.2 ms, 70 V supramaximal voltage, 10 s duration) produced contraction of perfused rabbit central ear arteries, and this contraction was reduced by incubation with insulin (0.6--200 mU/ml). This inhibitory effect of insulin was not significantly modified by removing the endothelium, or by treatment with N(W)-nitro-L-arginine (L-NA, 10(-4) M), meclofenamate (10(-5) M), ouabain (10(-6) M), or cocaine (10(-5) M). Insulin (200 mU/ml) did not modify the vascular contraction due to exogenous norepinephrine (10(-8)--10(-4) M) nor the relaxation due to acetylcholine (10(-8)--10(-4) M). This suggests that insulin may reduce vascular contraction by sympathetic stimulation, and this effect is not dependent on endothelial nitric oxide, prostanoids, or Na(+)--K(+) pump activation.

Basal inhibitory action of endogenous endothelin on the sympathetic contraction in the isolated rat tail artery.

In order to test whether endogenous endothelin modulates the sympathetic vasoconstriction, arterial segments, 2 mm long, from rat tail artery were mounted in organ baths for isometric tension recording. Electrical field stimulation (2-8 Hz, 0.2 ms, 70 V during 1 s) produced frequency-dependent arterial contraction (maximal contraction 770+/-49 mg) that was nearly abolished (over 95% reduction) by tetrodotoxin (10(-6) M) or phentolamine (10(-6) M). This contraction was increased by pretreatment with the antagonist of endothelin ET(B) receptors N-(N-(N-(2, 6-dimethyl-1-piperidinyl)carbonyl)-4-methyl-L-leucyl)-1-(methoxycarbo nyl)-D-tryptophyl)D-norleucine (BQ-788, 10(-7)-3x10(-6) M), and was not modified either by the antagonist of endothelin ET(A) receptors cyclo(D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl) (BQ-123, 10(-7)-3x10(-6) M) or the agonist of endothelin ET(B) receptors endothelin-1 (8-21), N-Suc-(Glu(9), Ala(11,15)) (IRL-1620, 10(-8)-10(-7) M). The potentiating effect of BQ-788 was not modified in arterial segments without endothelium or pretreated with the inhibitor of nitric oxide synthesis N(W)-nitro-L-arginine (L-NA, 10(-4) M) or with the inhibitor of endothelin converting enzyme N-(alpha-rhamnopyranosyloxy-hydroxyphosphinyl)-leu-trp (phosphoramidon, 10(-4) M). Exogenous noradrenaline (10(-9)-10(-4) M) produced concentration-dependent arterial contractions that were not modified by BQ-788 (3x10(-6) M), BQ-123 (3x10(-6) M) or IRL-1620 (10(-7) M). Therefore, an inhibitory action of endogenous endothelin on sympathetic vasoconstriction may be present under basal conditions. This inhibition could be produced by endothelin through activation of prejunctional endothelin ET(B) receptors, which may inhibit noradrenaline release from perivascular sympathetic nerves.

Effects of vasopressin on the sympathetic contraction of rabbit ear artery during cooling.

In order to analyse the effects of arginine-vasopressin on the vascular contraction to sympathetic nerve stimulation during cooling, the isometric response of isolated, 2-mm segments of the rabbit central ear (cutaneous) artery to electrical field stimulation (1-8 Hz) was recorded at 37 and 30 degrees C. Electrical stimulation (37 degrees C) produced frequency-dependent arterial contraction, which was reduced at 30 degrees C and potentiated by vasopressin (10 pM, 100 pM and 1 nM). This potentiation was greater at 30 than at 37 degrees C and was abolished at both temperatures by the antagonist of vasopressin V1 receptors d(CH2)5 Tyr(Me)AVP (100 nM). Desmopressin (1 microM) did not affect the response to electrical stimulation. At 37 degrees C, the vasopressin-induced potentiation was abolished by the purinoceptor antagonist PPADS (30 microM), increased by phentolamine (1 microM) or prazosin (1 microM) and not modified by yohimbine (1 microM), whilst at 30 degrees C, the potentiation was reduced by phentolamine, yohimbine or PPADS, and was not modified by prazosin. The Ca2+-channel blockers, verapamil (10 microM) and NiCl2 (1 mM), abolished the potentiating effects of vasopressin at 37 degrees C whilst verapamil reduced and NiCl2 abolished this potentiation at 30 degrees C. The inhibitor of nitric oxide synthesis, L-NOARG (100 microM), or endothelium removal did not modify the potentiation by vasopressin at 37 and 30 degrees C. Vasopressin also increased the arterial contraction to the alpha2-adrenoceptor agonist BHT-920 (10 microM) and to ATP (2 mM) at 30 and 37 degrees C, but it did not modify the contraction to noradrenaline (1 microM) at either temperature. These results suggest that in cutaneous (ear) arteries, vasopressin potentiaties sympathetic vasoconstriction to a greater extent at 30 than at 37 degrees C by activating vasopressin V1 receptors and Ca2+ channels at both temperatures. At 37 degrees C, the potentiation appears related to activation of the purinoceptor component and, at 30 degrees C, to activation of both purinoceptor and alpha2-adrenoceptor components of the sympathetic response.

Role of nitric oxide in the cerebral circulation during hypotension after hemorrhage, ganglionic blockade and diazoxide in awake goats.

The role of nitric oxide in cerebrovascular response to hypotension was analyzed by evaluating the changes in cerebrovascular resistance after inhibition of nitric oxide synthesis with Nw-nitro-L-arginine methyl ester (L-NAME) during three types of hypotension in conscious goats. Blood flow to one brain hemisphere was electromagnetically measured, hypotension was induced by controlled bleeding, and by i.v. administration of hexametonium (ganglionic blocker) or of diazoxide (vasodilator drug), and L-NAME was injected by i.v. route (35 mg kg-1). Under control conditions (13 goats), L-NAME increased arterial pressure from 98 +/- 3 to 123 +/- 4 mmHg and decreased cerebral blood flow from 65 +/- 3 to 40 +/- 3 ml min-1 (all P < 0.001); cerebrovascular resistance increased from 1.52 +/- 0.04 to 3.09 +/- 0.013 mmHg ml-1 min-1 (P < 0.01) (delta = 1.59 +/- 0.12 mmHg ml-1 min-1). After bleeding (five goats), mean arterial pressure decreased to 60 +/- 4 mmHg and cerebral blood flow decreased to 37 +/- 4 ml min-1 (all P < 0.01); cerebrovascular resistance did not change (1.56 +/- 0.14 vs. 1.54 +/- 0.12 mmHg ml-1 min-1, P > 0.05). During this hypotension, L-NAME increased arterial pressure to reach the normotensive values an did not affect the hypotensive values for cerebral blood flow; cerebrovascular resistance increased from the hypotensive values to 2.91 +/- 0.19 mmHg ml-1 min-1 (P < 0.01) (delta = 1.37 +/- 0.16 mmHg ml-1 min-1), and this increment is comparable to that under control conditions (P > 0.05). Ganglionic blockade (six goats) decreased arterial pressure to 67 +/- 2 mmHg) and did not affect significantly cerebral blood flow; cerebrovascular resistance decreased from 1.71 +/- 0.11 to 1.05 +/- 0.09 mmHg ml-1 min-1 (P < 0.01). During this hypotension, L-NAME increased arterial pressure to 103 +/- 6 mmHg (P < 0.001), and did not affect cerebral blood flow; cerebrovascular resistance increased from the hypotensive values to 1.68 +/- 0.18 mmHg ml-1 min-1 (P < 0.01) (delta = 0.63 +/- 0.10 mmHg ml-1 min-1), and this increment was lower than under control conditions (P < 0.01). Diazoxide (six goats) decreased arterial pressure to 69 +/- 5 mmHg (P < 0.01) without changing cerebral blood flow; cerebrovascular resistance decreased from 1.89 +/- 0.11 to 1.16 +/- 0.14 mmHg ml-1 min-1 (P < 0.01). During this hypotension, L-NAME increased arterial pressure to 87 +/- 6 mmHg (P < 0.05) and did not affect the hypotensive values for cerebral blood flow (P > 0.05); cerebrovascular resistance increased from the hypotensive values to 1.53 +/- 0.13 mmHg ml-1 min-1 (P < 0.05) (delta = 0.36 +/- 0.06 mmHg-1 ml-1 min-1), and this increment was lower than under control conditions (P < 0.01). Therefore, the role of nitric oxide in cerebrovascular response to hypotension may differ in each type of hypotension, as this role during hemorrhagic hypotension may not change and during hypotension by ganglionic blockade or diazoxide may decrease. These differences may be related to changes in nitric oxide release as stimuli on the endothelium (shear stress and sympathetic activity) may vary in each type of hypotension.

Effects of hyperthermia on contraction and dilatation of rabbit femoral arteries.

To analyze the effect of hyperthermia on the vascular response, the isometric response of isolated rabbit femoral artery segments was recorded at 37 degreesC and hyperthermia (41 and 44 degreesC). Contraction to potassium (5 x 10(-3)-5 x 10(-2) M) was significantly greater at 41 and 44 than at 37 degreesC and increased by inhibition of nitric oxide (NO) synthesis with Nomega-nitro-L-arginine (L-NNA; 10(-4) M) or endothelium removal at 37 degreesC but not at 41 or 44 degreesC. Norepinephrine (10(-9)-10(-4) M) produced a concentration-dependent contraction greater at 41 or 44 than at 37 degreesC and not modified by endothelium removal or L-NNA at either temperature. Phenylephrine (10(-9)-10(-4) M) produced a contraction increased by warming to 44 degreesC but not to 41 degreesC. The specific alpha2-adrenoceptor agonist BHT-920 produced a weak contraction, reduced by the alpha1-adrenoceptor antagonist prazosin (10(-6) M) and increased at 44 degreesC but not at 41 degreesC. The concentration-dependent contraction to endothelin-1 (ET-1; 10(-11)-10(-7) M) was increased by warming to 41 and 44 degreesC and by endothelium removal or L-NNA at 37 degreesC but not at 41 or 44 degreesC. Response to ET-1 was reduced by endothelin ETA-receptor antagonist BQ-123 (10(-5) M) and ETB-receptor antagonist BQ-788 (10(-5) M). In arteries precontracted with ET-1 (10(-8)-3 x 10(-8) M), relaxation to sodium nitroprusside (10(-8)-10(-4) M) was increased at 41 and 44 degreesC vs. at 37 degreesC, but that of ACh (10(-8)-10(-4) M) or adenosine (10(-8)-10(-4) M) was not different at all temperatures studied. Relaxation to ACh, but not adenosine, was reduced similarly by L-NNA at all temperatures studied. These results suggest hyperthermia in muscular arteries may inhibit production of, and increase dilatation to, NO, resulting in unchanged relaxation to ACh and increased constriction to KCl and ET-1, and may increase constriction to stimulation of alpha1-adrenoceptors by NO-independent mechanisms.

Adrenergic reactivity after inhibition of nitric oxide synthesis in the cerebral circulation of awake goats.

The interaction between nitric oxide (NO) and adrenergic reactivity in the cerebral circulation was studied using in vivo and in vitro preparations. Blood flow to one brain hemisphere (cerebral blood flow) was electromagnetically measured in conscious goats, and the effects of norepinephrine, tyramine and cervical sympathetic nerve stimulation were recorded before (control) and after inhibition of NO formation with Nw-nitro-l-arginine methyl ester (l-NAME). The responses to norepinephrine, tyramine and electrical field stimulation were also recorded in segments, 4 mm in length, from the goat's middle cerebral artery under control conditions and after l-NAME. In vivo, l-NAME (10 goats, 47 mg kg-1 administered i.v.) reduced resting cerebral blood flow by 37+/-2%, increased mean systemic arterial pressure by 24+/-3%, reduced heart rate by 35+/-2%, and decreased cerebrovascular conductance by 52+/-2% (all P<0.01). Norepinephrine (0.3-9 microgram), tyramine (50-500 microgram), and supramaximal electrical sympathetic cervical nerve stimulation (1. 5-6 Hz) decreased cerebrovascular conductance, and these decreases were significantly higher after l-NAME than under control conditions, remaining higher for about 48 h after this treatment. Norepinephrine (10-8-10-3 M), tyramine (10-6-10-3 M) and electrical field stimulation (1.5-6 Hz) contracted isolated cerebral arteries, and the maximal contraction, but not the sensitivity, was significantly higher in the arteries treated than in non-treated with l-NAME (10-4 M). Therefore, the reactivity of cerebral vasculature to exogenous and endogenous norepinephrine may be increased after inhibition of NO synthesis. This increase might be related, at least in part, to changes at postjunctional level in the adrenergic innervation of the vessel wall, and it might contribute to the observed decreases in resting cerebral blood flow after inhibition of NO synthesis.

In vivo and in vitro action of endothelin-1 on goat cerebrovascular bed.

This study concerned the effects and mechanisms of action of endothelin-1 on the cerebral circulation. Cerebral blood flow was electromagnetically measured in awake goats. Endothelin-1 (0.01-0.3 nmol) produced dose-dependent decreases in this flow (maximal reduction = 34%) and increases in cerebrovascular resistance (maximal increase = 74%) (P < 0.01). IRL 1620 (Suc-[Glu9, Ala11,15]endothelin-1-(8-21), agonist for endothelin ET(B) receptors, 0.01-0.3 nmol) slightly decreased cerebral blood flow. The effects of endothelin-1, but not those of IRL 1620, on cerebral blood flow were diminished by 50% during infusion of the antagonist for endothelin ET(A) receptors, BQ-123 (cyclo-(D-Asp-Pro-D-Val-Leu-Trp), 2 nmol min(-1)), but not affected during infusion of the antagonist for endothelin ET(B) receptors, BQ-788 (N-[N-[N-[(2,6-dimethyl-1-piperidinyl)carbonyl]-4-methyl-L-Leucyl-1-(met hoxycarbonyl)-D-tryptophyl]-Dnorleucine monosodium), 2 nmol min(-1)). Intravenous administration of NW-nitro-L-arginine methyl ester (L-NAME, 47 mg kg(-1)) or NW-nitro-L-arginine (L-NNA, 47 mg kg(-1)) reduced basal cerebral blood flow by 39 and 33%, increased cerebrovascular resistance by 108 and 98% and mean arterial pressure by 23 and 17%, and decreased heart rate by 27 and 25%, respectively (all at least P < 0.05). The increases in cerebrovascular resistance (as absolute values) induced by endothelin-1 were not affected during either L-NAME or L-NNA (as absolute values and percentages). Intravenous administration of meclofenamate (5 mg kg(-1)) did not change the cerebrovascular effects of endothelin-1 and IRL 1620. In isolated goat cerebral arteries under control, resting conditions, endothelin-1 (10(-11)-10(-7) M) induced concentration-dependent contractions (EC50 = 4.78 X 10(-9) M; maximal contraction = 3177+/-129 mg), whereas IRL 1620 (10(-11)-10(-7) M) produced no effect. This contraction produced by endothelin-1 was competitively blocked by BQ-123 (10(-7)-3 X 10(-6) M), and was not affected by BQ-788 (10(-6) and 10(-5) M). L-NAME (10(-4) M), meclofenamate (10(-5) M), indomethacin (10(-5) M), L-NAME (10(-4) M) plus meclofenamate (10(-5) M) and phosphoramidon (10(-4) M) did not affect the contraction in response to endothelin-1. Endothelium removal increased the response to endothelin-1, as well as the BQ-123 antagonism against endothelin-1 (pA2 values, 7.62 vs. 6.88; P < 0.01). In both intact and de-endothelized arteries precontracted with prostaglandin F2alpha endothelin-1 induced a further contraction, and IRL 1620 caused no effect. These results suggest that: (1) endothelin-1 produces cerebral vasoconstriction by activating endothelin ET(A) receptors probably located in smooth muscle; (2) endothelin ET(B) receptors, nitric oxide and prostanoids might be not involved in the cerebrovascular action of endothelin-1, and (3) endothelium removal may increase cerebrovascular reactivity by increasing sensitivity of endothelin ET(A) receptors to endothelin-1.

PCA50941, a new 1,4-dihydropyridine, reverses endothelin-induced cardiogenic shock in the anesthetized goat.

This study was designed to test the hypothesis that the properties of novel 1,4-dihydropyridine PCA50941 could favor the recovery of cardiogenic shock. Coronary blood flow (CBF), measured with an electromagnetic flow probe placed on the left circumflex coronary artery, systemic arterial pressure and heart rate were recorded in 24 anesthetized goats; left ventricular pressure and dP/dt were also recorded in 19 of these goats. Under control conditions, intracoronary injections in 5 goats of PCA50941 (10-120 microg) caused smaller reductions of CBF than those of Bay K 8644 (0.3-10 microg) (the reduction of CBF by 120 microg PCA50941 was 25% and that by 10 microg Bay K 8644 was 43%), and i.v. infusions in 4 goats of PCA50941 (10-300 microg/min) did not modify CBF nor the other hemodynamic variables recorded, whereas i.v infusion of Bay K 8644 (10-30 microg/min) reduced CBF by 20% and increased arterial pressure, left ventricular pressure and dP/dt. During control conditions and endothelin-induced cardiogenic shock, respectively, the values for 15 goats were: for CBF, 33+/-4 vs. 16+/-4 ml/min; for mean arterial pressure, 88+/-4 vs. 60+/-5 mm Hg; for left ventricular systolic pressure, 102+/-5 vs. 75+/-4 mm Hg; for dP/dt, 1453+/-147 vs. 925+/-101 mm Hg/s (all P<0.05), and for heart rate, 77+/-6 vs. 81+/-6 beats/min (P>0.05). Intravenous infusion of PCA50941 (100 microg/min) reversed the hemodynamic variables from the shock state to control values within 20 min in 5 of 6 animals, whereas i.v. administration of Bay K 8644 (10-30 microg/min) was not effective in 4 of 5 animals, and the vehicle (DMSO) was not effective in none of 4 animals in reversing the hemodynamic shock state. Therefore, it is suggested that PCA50941, a novel 1,4-dihydropyridine, has a cardiovascular profile that might be suitable for treating cardiogenic shock states.

Coronary vasoconstriction produced by vasopressin in anesthetized goats. Role of vasopressin V1 and V2 receptors and nitric oxide.

To examine the role of vasopressin V1 and V2 receptors, nitric oxide and prostanoids in the coronary vascular effects of [Arg8]vasopressin, coronary blood flow was measured with an electromagnetic flow transducer placed around the left circumflex (23 goats) or anterior descending (11 goats) coronary artery and vasopressin (0.03-1 microg) was intracoronarily injected in 34 anesthetized, open-chest goats. Basal mean values for coronary blood flow, mean systemic arterial pressure and heart rate, were 34 +/- 2.38 ml/min, 89 +/- 3.34 mmHg and 80 +/- 3.06 beats/min, respectively. Vasopressin produced dose-dependent decreases in coronary blood flow and the maximal reduction of this flow, attained with 1 microg of vasopressin, was 14 +/- 1.49 ml/min (42 +/- 2.64% of basal flow) (P < 0.01). Desmopressin (0.03-1 microg; 8 goats) did not affect significantly coronary blood flow. The intracoronary infusion of the antagonist for vasopressin V1 receptors d(CH2)5Tyr (Me) arginine vasopressin (2 microg/min per kg, 6 animals) significantly diminished the effects of vasopressin on coronary blood flow (the effects of 1 microg of vasopressin were reduced by 28%, P < 0.05). The mixed antagonist for vasopressin V1 and V2 receptors desGly-d(CH2)5-D-Tyr(Et)Val arginine vasopressin (0.2, 0.7 and 2 microg/min per kg, 9 animals) decreased in a dose-dependent manner the effects of vasopressin on coronary blood flow (the effects of 1 microg of vasopressin were decreased by 61% with 2 microg/min per kg, P < 0.01). Intracoronary infusion of saline (vehicle, 3 goats) did not change the effects of vasopressin on coronary blood flow. Intravenous administration of the inhibitor of nitric oxide synthesis N-omega-nitro-L-arginine methyl ester (L-NAME, 47 mg/kg, 9 animals) decreased resting coronary blood flow by 10% (P < 0.01) and augmented mean systemic arterial pressure by 20% (P < 0.01), without changing heart rate. During this treatment the reduction in coronary blood flow produced by vasopressin was higher than under control (the effects of 1 microg of vasopressin were increased by 28%, P < 0.01). Intravenous administration of the inhibitor of cyclooxygenase, meclofenamate (5 mg/kg, 7 animals), neither modified resting coronary blood flow, arterial pressure and heart rate nor the effects of vasopressin on this flow. These data indicate that vasopressin produces marked coronary vasoconstriction and suggest that: (a) it may be mediated by vasopressin V1 receptors, without involvement of vasopressin V2 receptors, (b) it is probably inhibited by nitric oxide under normal conditions and (c) it may be not modulated by prostanoids.

Role of the purinergic and noradrenergic components in the potentiation by endothelin-1 of the sympathetic contraction of the rabbit central ear artery during cooling.

1. To examine the role of the purinergic and noradrenergic components in the potentiation of endothelin-1 on the vascular response to sympathetic nerve stimulation, we recorded the isometric response of isolated segments, 2 mm long, from the rabbit central ear artery to electrical field stimulation (1-8 Hz) under different conditions, at 37 degrees C during cooling (30 degrees C). 2. Electrical field stimulation produced frequency-dependent contraction, which was reduced during cooling (about 60% for 8 Hz). Both at 37 degrees C and 30 degrees C, phentolamine (1 microM) or blockade of alpha(1)-adrenoceptors with prazosin (1 microM) reduced, whereas blockade of alpha(2)-adrenoceptors with yohimbine (1 microM) increased, the contraction to electrical field stimulation. This contraction was increased after desensitization of P2-receptors with alpha, beta-methylene adenosine 5'-triphosphate (alpha, beta-meATP, 3 microM) at 37 degrees C but not at 30 degrees C, and was not modified by blockade of P2-receptors with pyridoxalphosphate-6-azophenyl-2,4'-disulphonic acid (PPADS, 30 microM) at either temperature. 3. Endothelin-1 (1, 3 and 10 nM) at 37 degrees C did not affect, but at 30 degrees C it potentiated in a concentration-dependent manner the contraction to electrical field stimulation (from 28 +/- 6 to 134 +/- 22%, for 8 Hz). At 37 degrees C, endothelin-1 in the presence of phentolamine or prazosin, but not in that of yohimbine, alpha, beta-meATP or PPADS, potentiated the contraction to electrical stimulation. At 30 degrees C, phentolamine or yohimbine reduced, prazosin did not modify and alpha, beta-meATP slightly increased the potentiation by endothelin-1 of the response to electrical stimulation. 4. The arterial contraction to ATP (2 mM) and the alpha(2)-adrenoceptor agonist BHT-920 (10 microM), but not that to (-)-noradrenaline (1 microM), was potentiated by endothelin-1 at both 37 degrees C and 30 degrees C. 5. These results in the rabbit central ear artery suggest that the sympathetic response: (a) at 37 degrees C, could be mediated mainly by activation of alpha(1)-adrenoceptors, with low participation of P2-receptors, (b) is diminished during cooling, probably by a reduction in the participation of alpha(1)-adrenoceptors, and in this condition the response could be mediated in part by P2-receptors, and (c) is potentiated by endothelin-1 during cooling, probably by increasing the response of both postjunctional alpha(2)-adrenoceptors and P2-receptors.

Role of endothelin receptors, calcium and nitric oxide in the potentiation by endothelin-1 of the sympathetic contraction of rabbit ear artery during cooling.

1. To examine further the potentiation by endothelin-1 on the vascular response to sympathetic stimulation, we studied the isometric response of isolated segments, 2 mm long, from the rabbit central ear artery to electrical field stimulation (1-8 Hz), under different conditions, at 37 degrees C and during cooling (30 degrees C). 2. Electrical stimulation produced frequency-dependent contraction, which was reduced (about 63% for 8 Hz) during cooling. At 30 degrees C, but not at 37 degrees C, endothelin-1 (1, 3 and 10 nM) potentiated the contraction to electrical stimulation in a dose-dependent way (from 43 +/- 7% to 190 +/- 25% for 8 Hz). 3. This potentiation by endothelin-1 was reduced by the antagonist for endothelin ETA receptors BQ-123 (10 microM) but not by the antagonist for endothelin ETB receptors BQ-788 (10 microM). The agonist for endothelin ETB receptors IRL-1620 (0.1 microM) did not modify the contraction to electrical stimulation. 4. The blocker of L-type Ca2+ channels verapamil (10 microM l-1) reduced (about 72% for 8 Hz) and the unspecific blocker of Ca(2+)-channels NiCl2 (1 mM) practically abolished (about 98%), the potentiating effects of endothelin-1 found at 30 degrees C. 5. Inhibition of nitric oxide synthesis with NG-nitro-L-arginine (L-NOARG, 0.1 mM) increased the contraction to electrical stimulation at 30 degrees C more than at 37 degrees C (for 8 Hz, this increment was 297 +/- 118% at 30 degrees C, and 66 +/- 15% at 37 degrees C). Endothelium removal increased the contraction to electrical stimulation at 30 degrees C (about 91% for 8 Hz) but not at 37 degrees C. Both L-NOARG and endothelium removal abolished the potentiating effects of endothelin-1 on the response to electrical stimulation found at 30 degrees C. 6. These results in the rabbit ear artery suggest that during cooling, endothelin-1 potentiates the contraction to sympathetic stimulation, which could be mediated at least in part by increasing Ca2+ entry after activation of endothelin ETA receptors. This potentiating effect of endothelin-1 may require the presence of an inhibitory tone due to endothelial nitric oxide.

Role of nitric oxide in the effects of hypoglycemia on the cerebral circulation in awake goats.

This study was performed to examine the role of nitric oxide in the effects of hypoglycemia on the cerebral circulation. Hypoglycemia was induced with insulin and its effects on cerebral blood flow (measured with an electromagnetic flow transducer placed on the internal maxillary artery) were studied in awake goats under control conditions and after administration of the nitric oxide synthesis inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 47 mg/kg). Also, cerebrovascular reactivity to vasodilator stimuli was examined during insulin-induced severe hypoglycemia, before and after L-NAME treatment. In five animals under control conditions (glycemia = 90 +/- 7 mg/dl, cerebral blood flow = 64 +/- 4 ml/min, mean systemic arterial pressure = 102 +/- 4 mmHg, cerebrovascular resistance = 1.62 +/- 0.11 mmHg/ml per min and heart rate = 73 +/- 6 beats/min), insulin decreased glycemia: when hypoglycemia was moderate (glycemia = 46 +/- 2 mg/dl) or severe (glycemia = 26 +/- 1 mg/dl) cerebral blood flow increased by 25 +/- 4% and 47 +/- 6%, and cerebrovascular resistance decreased by 18 +/- 3% and 34 +/- 4%, respectively. Under basal conditions, L-NAME did not affect glycemia but reduced resting cerebral blood flow by 37 +/- 2%, increased mean arterial pressure by 33 +/- 2% and decreased heart rate by 28 +/- 3%; after L-NAME, both moderate and severe hypoglycemia did not alter significantly resting cerebral blood flow and cerebrovascular resistance. In five other goats, L-NAME, administered during severe hypoglycemia, abolished the increase in cerebral blood flow, and increased cerebrovascular resistance and mean arterial pressure over the control (normoglycemic) values. In these animals with severe hypoglycemia, acetylcholine (0.01-1 microg), isoproterenol (0.03-3 microg) and diazoxide (0.3-9 mg), injected into the internal maxillary artery, decreased cerebrovascular resistance in a dose-dependent manner, and this decrease was similar before and after L-NAME. Therefore, insulin-induced hypoglycemia may produce cerebral vasodilatation by releasing nitric oxide and may diminish the capacity of the cerebral vasculature to release nitric oxide in response to acetylcholine.