Coronary response to diadenosine triphosphate after ischemia-reperfusion in the isolated rat heart.

Diadenosine triphosphate (Ap3A) is a vasoactive mediator stored in platelet granules that may be released during coronary ischemia-reperfusion. To study its coronary effects in such circumstances, rat hearts were perfused in a Langendorff preparation and the coronary response to Ap3A (10(-7)-10(-5) mol/L) was recorded. Both at basal coronary resting tone and after precontraction with 11-dideoxy-1a,9a-epoxymethanoprostaglandin F(2)(α) (U46619), Ap3A produced concentration-dependent vasodilation in the heart, which was attenuated following ischemia-reperfusion. Ap3A-induced relaxation was also attenuated in control conditions and after ischemia-reperfusion by the purinergic P2Y antagonist reactive blue 2 (2 × 10(-6) mol/L), the P2Y(1) antagonist MRS 2179 (10(-5) mol/L), the nitric oxide synthesis inhibitor N-omega-nitro-l-arginine methyl ester (l-NAME; 10(-4) mol/L) and the ATP-dependent potassium channel blocker glibenclamide (10(-5) mol/L). These results suggest that Ap3A induces coronary vasodilation, an effect attenuated by ischemia-reperfusion due to the functional impairment of purinergic P2Y receptors and K(ATP) channels, and/or reduced nitric oxide release. This impairment of vasodilation may contribute to the coronary dysregulation that occurs during ischemia-reperfusion.

Nitric oxide-mediated relaxation to lactate of coronary circulation in the isolated perfused rat heart.

The objective of this study was to analyze the effects of lactate on coronary circulation. Rat hearts were perfused in a Langendorff preparation, and the coronary response to lactate (3-30 mM) was recorded after precontracting coronary vasculature with 11-dideoxy-1a,9a-epoxymethanoprostaglandin F2α (U46619), in the presence or the absence of the inhibitor of nitric oxide synthesis, N-omega-nitro-l-arginine methyl ester (l-NAME, 10 M), the blocker of Ca-dependent potassium channels, tetraethylammonium (TEA, 10 M), or the blocker of adenosine triphosphate-sensitive potassium channels, glybenclamide (10 M). The effects of lactate were also studied in isolated segments of rat coronary arteries that were precontracted with U46619, with or without endothelium. In perfused hearts, lactate induced concentration-dependent coronary vasodilatation and a reduction in myocardial contractility (left ventricular developed pressure and dP/dt) without altering the heart rate. Coronary vasodilatation in response to lactate was reduced by l-NAME but unaffected by TEA or glybenclamide. The effects of lactate on myocardial contractility were unchanged by l-NAME, TEA, or glybenclamide. In isolated coronary artery segments, lactate also produced relaxation, an effect attenuated by removing the endothelium. Together these findings suggest that lactate exerts coronary vasodilatory effects through the release of endothelial nitric oxide, independently of potassium channels. These findings may be relevant for the regulation of coronary circulation when lactate levels are elevated.

Dilator and constrictor response of renal vasculature during acute renal hypotension in anesthetized goats. Role of nitric oxide.

The relative role of NO derived from endothelium NO synthase (eNOS) and neuronal NO synthase (nNOS) in renovascular reactivity during renal hypotension is unknown. To examine this issue, we recorded the effects of unspecific inhibitor of NO synthase N(w)-nitro-L-arginine methyl esther (L-NAME) and inhibitor of nNOS 7-nitroindazole monosodium salt (7-NINA) on renal vasodilator and vasoconstrictor responses in anesthetized goats during renal hypotension by constricting the abdominal aorta. Intrarenal administration of L-NAME and hypotension, either untreated or treated with L-NAME, decreased resting renal blood flow, and the increases in renal blood flow by acetylcholine but not those by sodium nitroprusside were tempered, and the decreases by norepinephrine and angiotensin II were augmented. Intraperitoneal administration of 7-NINA did not affect, and 7-NINA+hypotension decreased renal blood flow, and under these conditions the increases in renal blood flow by acetylcholine and sodium nitroprusside were not modified, and the decreases by norepinephrine and angiotensin II were slightly (during 7-NINA) or consistently augmented (7-NINA+hypotension). Therefore, NO derived from eNOS plays a significant role, while that derived from nNOS plays a little role, if any, to regulate renal blood flow and to mediate acetylcholine-induced vasodilation, as well to modulate renal vasoconstriction by norepinephrine and angiotensin II.

Coronary response to diadenosine tetraphosphate after ischemia-reperfusion in the isolated rat heart.

Diadenosine tetraphosphate (AP4A) is a vasoactive mediator that may be released from platelet granules and that may reach higher plasma concentrations during coronary ischemia-reperfusion. The objective of this study was to analyze its coronary effects in such conditions. To this, rat hearts were perfused in a Langendorff preparation and the coronary response to Ap4A (10(-7)-10(-5) M) was recorded. In control hearts, Ap4A produced concentration-dependent vasodilatation both at the basal coronary resting tone and after precontracting coronary vasculature with 11-dideoxy-1a,9a-epoxymethanoprostaglandin F2α (U46619), and this vasodilatation was reduced by reactive blue 2 (2×10(-6) M), glibenclamide (10(-5) M), H89 (10(-6) M), U73122 (5×10(-6) M) and endothelin-1 (10(-9) M), but not by L-NAME (10(-4) M), isatin (10(-4) M), GF109203x (5×10(-7) M), or wortmannin (5×10(-7) M). After ischemia-reperfusion, the vasodilatation to Ap4A diminished, both in hearts with basal or increased vascular tone, and in this case the relaxation to Ap4A was not modified by reactive blue 2, L-NAME, glibenclamide, isatin, H89, GF109203x or wortmannin, although it was reduced by U73122 and endothelin-1. UTP produced coronary relaxation that was also reduced after ischemia-reperfusion. These results suggest that the coronary relaxation to Ap4A is reduced after ischemia-reperfusion, and that this reduction may be due to impaired effects of KATP channels and to reduced response of purinergic P2Y receptors.

Role of alpha-adrenoceptors and prostacyclin in the enhanced adrenergic reactivity of goat cerebral arteries after ischemia-reperfusion.

To analyze ischemia-reperfusion effects on the cerebrovascular adrenergic response, the left middle cerebral artery (MCA) of anesthetized goats was occluded for 120 min and reperfused for 60 min. Isolated segments from the left (ischemic) and right (control) MCA exhibited isometric constriction in response to noradrenaline (10(-8)-10(-4)M, in the presence of beta-adrenoceptors blockade), phenylephrine (alpha(1)-adrenoceptors agonist, 10(-8)-10(-4)M), B-HT-920 (alpha(2)-adrenoceptors agonist, 10(-7) - 3 x 10(-3)M) or tyramine (indirect sympatheticomimetic amine, 10(-8)-10(-4)M), but this constriction was greater in ischemic arteries. The cyclooxygenase (COX) inhibitor meclofenamate (10(-5)M) augmented the response to noradrenaline only in control arteries. The prostacyclin (PGI(2)) synthesis inhibitor tranylcypromine (TCP, 10(-5)M) increased the response to noradrenaline in control arteries and reduced it in ischemic arteries. The thromboxane A(2) (TXA(2)) synthase inhibitor furegrelate (10(-6)M) did not modify the noradrenaline effect in both types of arteries, whereas the TXA(2) receptor antagonist SQ 29 548 (10(-5)M) and the COX-2 inhibitor NS-398 (10(-6)M) decreased the response to noradrenaline only in ischemic arteries. PGI(2) caused a small relaxation in control arteries and a small contraction in ischemic arteries. alpha-Adrenoceptors and COX-2 protein expression and the metabolite of PGI(2) were augmented in ischemic arteries. Therefore, ischemia-reperfusion may increase the cerebrovascular responsiveness to noradrenaline, through upregulation of alpha-adrenoceptors and increased COX-2-derived PGI(2) exerting a vasoconstrictor action. After ischemia-reperfusion, noradrenaline might increase PGI(2) production thus contributing to adrenergic vasoconstriction and/or PGI(2) would potentiate the noradrenaline effects.

Effects of endothelin-1 on the relaxation of rat coronary arteries.

To analyze the effects of endothelin-1 on the b-adrenergic response of the coronary circulation, 2-mm-long segments of coronary arteries from rats were prepared for isometric tension recording in organ baths. The relaxation to isoproterenol (3 x 10(-8) M), field electrical stimulation (4 Hz, 0.1-millisecond duration, 10 seconds), acetylcholine (3 x 10(-8) M), and sodium nitroprusside (10(-9) M) was recorded in arteries precontracted with U46619 (10(-7) to 5 x 10(-7) M) before and after treatment with endothelin-1 (3 3 10210 and 1029 M). The relaxation to isoproterenol was increased by treatment with endothelin-1 and with the endothelin ET(B) antagonist BQ788 (10(-6) M) but not with the endothelin ET(A) antagonist BQ123 (10(-6) M) or with the blocker of protein kinase C chelerythrine (10(-5) M). In the presence of BQ788, BQ123, or chelerythrine, endothelin-1 did not modify the relaxation to isoproterenol. Treatment with endothelin-1 did not modify the relaxation to electrical stimulation, acetylcholine, or sodium nitroprusside. These results suggest that endothelin-1 may potentiate coronary beta-adrenergic vasodilatation, at least in part due to stimulation of endothelin ET(A) receptors and activation of protein kinase C.

Role of angiotensin II in the response to endothelin-1 of goat cerebral arteries after ischemia-reperfusion.

As angiotensin II may underlie the deleterious effects of some vascular diseases, we have examined the role of this peptide on the cerbrovascular endothelin-1 action after ischemia-reperfusion. In anesthetized goats, 1 hour-occlusion followed by 1 hour-reperfusion of the left middle cerebral artery (MCA) was induced, and then segments 3-mm in length from branches of the right MCA (control) and the left MCA (ischemic) were obtained for isometric tension recording. Endothelin-1 (10(-11)-10(-7) M) produced a contraction that was higher in ischemic than in control arteries, and in control but not in ischemic arteries this contraction was potentiated by angiotensin II (10(-7) M). Losartan (3 x 10(-6) M), antagonist of AT1 receptors, did not affect the response to endothelin-1 in control arteries, but reduced it both in ischemic arteries and angiotensin II-treated control arteries. PD123,319 (3 x 10(-6) M), antagonist of AT2 receptors, or the inhibitor of nitric oxide synthesis L-NAME (10(-4) M) did not alter the arterial effects of endothelin-1. Therefore, angiotensin II may potentiate the constriction to endothelin-1 in normal cerebral arteries by activating AT1 receptors. The observed cerebrovascular increased response to endothelin-1 after ischemia-reperfusion might be related in part to activation of AT1 receptors under this condition.

Coronary response to diadenosine pentaphosphate after ischaemia-reperfusion in the isolated rat heart.

AIMS: Diadenosine polyphosphates are vasoactive mediators that may be released from platelet granules and which may be present at higher concentrations during coronary ischaemia-reperfusion. The objective of this study was to analyse their effects in such conditions. METHODS AND RESULTS: Rat hearts were perfused in a Langendorff preparation and the response to diadenosine pentaphosphate (Ap5A, 10(-7)-10(-5) M) was recorded. In control hearts, Ap5A produced a small, transient coronary vasoconstriction followed by marked vasodilatation, as well as a reduction in the left ventricular developed pressure dP/dt and heart rate, both at the basal coronary resting tone or after pre-contracting coronary arteries with 9,11-dideoxy-11alpha, 9alpha-epoxymethanoprostaglandin F2alpha (U46619). After ischaemia-reperfusion, the vasoconstriction in response to Ap5A was augmented and vasodilatation diminished, both in hearts with basal or increased vascular tone. The pyridoxal derivative P(2) purinoceptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, 3 x 10(-6) M), inhibited this vasoconstriction, while the antagonist of purinergic P(2Y) receptors, Reactive Blue 2 (2 x 10(-6) M), inhibited the vasodilatation, both before and after ischaemia-reperfusion. The antagonist of nitric oxide synthesis N-omega-nitro-L- arginine methyl ester (L-NAME, 10(-4) M) did not modify the response to Ap5A, whereas the cyclooxygenase inhibitor, meclofenamate (2 x 10(-6) M), reduced contraction and increased the relaxation in response to Ap5A after ischaemia-reperfusion but not under control conditions. CONCLUSION: Ischaemia-reperfusion reduces the vasodilatory response to Ap5A and increases the vasoconstriction provoked due to a reduced influence of purinergic P(2Y) receptors and/or to the production of vasoconstrictor prostanoids.

Response to endothelin-1 in arteries from human colorectal tumours: role of endothelin receptors.

To examine the reaction of tumour arteries to endothelin-1, we obtained arteries supplying blood flow to colorectal tumours from patients, as well as mesenteric arteries supplying the normal colon tissue from the same patients and mesenteric arteries from patients without a colorectal tumour pathology. The contraction in response to endothelin-1 and the relaxation produced by bradykinin was recorded in each of these arteries. Accordingly, the sensitivity to endothelin-1 but not the maximal response, was higher in the arteries supplying colorectal tumours than in mesenteric arteries supplying normal colon or in mesenteric arteries from patients with no tumour pathology. The contraction produced by endothelin-1 was not modified by exposure to L-NAME or meclofenamate in arteries supplying both the tumour and the normal colon. The endothelin ET(A) andET(B) receptors were expressed similarly in arteries supplying the tumour or normal colon. However, the antagonist of the endothelin ET(B) receptors BQ788 (10(-6) M) decreased the contractions in the arteries supplying the tumour but not in those supplying the normal colon. By contrast, the antagonist of endothelin ET(A) receptors BQ123 (10(-6) M) reduced the contraction equally in both these types of arteries. Likewise, in arteries precontracted with U46619, the relaxation in response to bradykinin was similar in all three types of arteries. Together, these results suggest that the arteries supplying human colorectal tumours are more sensitive to endothelin-1, which could be due to the enhanced activity of endothelin ET(B) receptors in the absence of any change in the modulatory effect of nitric oxide or prostanoids in the arterial response to this peptide.

Endothelin-1 potentiation of coronary artery contraction after ischemia-reperfusion.

Hearts from Sprague-Dawley rats were perfused at constant flow and then exposed to 30 min global zero-flow ischemia followed by 15 min reperfusion. After ischemia-reperfusion, coronary arteries were dissected from the heart and segments 2 mm long were prepared for isometric tension recording in organ baths. Stimulation of the arteries with 5-hydroxytryptamine (10(-6) M) produced contraction, which was potentiated by treatment with endothelin-1 (3x10(-10); 10(-9) M). This potentiation was lower in the arteries from hearts after ischemia-reperfusion (for 3x10(-10) M, 15+/-5%; P>0.05; for 10(-9) M, 37+/-7%, P<0.01, n=5) than after control (for 3x10(-10) M, 34+/-4%; P<0.01; for 10(-9) M, 50+/-6%, P<0.01, n=5), and the potentiation was reduced by the inhibitor of nitric oxide synthesis l-NAME (10(-4) M), the antagonist of endothelin ET(A) receptors BQ123 (10(-6) M) and the antagonist of endothelin ET(B) receptors BQ788 (10(-6) M), but not by the cyclooxygenase inhibitor meclofenamate (10(-5) M). These results suggest that endothelin-1 at low concentrations potentiates coronary vasoconstriction, and this effect is reduced after ischemia-reperfusion, mediated by endothelin ET(A) and ET(B) receptors and dependent on nitric oxide release.

Adrenergic response of splanchnic arteries from cirrhotic patients: role of nitric oxide, prostanoids, and reactive oxygen species.

Peripheral and splanchnic vasodilatation in cirrhotic patients has been related to hyporesponsiveness to vasoconstrictors, but studies to examine the vascular adrenergic response provide contradictory results. Hepatic arteries from cirrhotic patients undergoing liver transplantation and mesenteric arteries from liver donors were obtained. Segments 3 mm long from these arteries were mounted in organ baths for testing isometric adrenergic response. The concentration-dependent contraction to noradrenaline (10(-8) to 10(-4) M) was similar in hepatic and mesenteric arteries, and prazosin (alpha 1-adrenergic antagonist, 10(-6) M), but not yohimbine (alpha 2-adrenergic antagonist, 10(-6) M), produced a rightward parallel displacement of this contraction in both types of arteries. Phenylephrine (alpha 1-adrenergic agonist, 10(-8) to 10(-4) M) and clonidine (alpha 2-adrenergic agonist, 10(-8) to 10(-4) M) also produced concentration-dependent contractions that were comparable in hepatic and mesenteric arteries. The inhibitor of cyclooxygenase meclofenamate (10(-5) M), but not the inhibitor of nitric oxide synthesis N(w)-nitro-l-arginine methyl ester (l-NAME, 10(-4) M), potentiated the response to noradrenaline in hepatic arteries; neither inhibitor affected the response to noradrenaline in mesenteric arteries. Diphenyleneiodonium (DPI; 5 x 10(-6) M), but neither catalase (1000 U/ml) nor tiron (10(-4) M), decreased the maximal contraction for noradrenaline similarly in hepatic and mesenteric arteries. Therefore, it is suggested that, in splanchnic arteries from cirrhotic patients, the adrenergic response and the relative contribution of alpha 1- and alpha 2-adrenoceptors in this response is preserved, and prostanoids, but not nitric oxide, may blunt that response. Products dependent on NAD(P)H oxidase might contribute to the adrenergic response in splanchnic arteries from control and cirrhotic patients.

Apelin effects in human splanchnic arteries. Role of nitric oxide and prostanoids.

Apelin effects were examined in human splanchnic arteries from liver donors (normal arteries) and from liver recipients. Segments 3 mm long were obtained from mesenteric arteries taken from liver donors (normal arteries), and from hepatic arteries taken from cirrhotic patients undergoing liver transplantation (liver recipients), and the segments were mounted in organ baths for isometric tension recording. In arteries under resting conditions, apelin (10(-10)-10(-6) M) caused no effect in any of the arteries tested. In arteries precontracted with the thromboxane A(2) analogue U46619 (10(-7)-10(-6) M), apelin (10(-10)-10(-6) M) produced concentration-dependent relaxation that was lower in hepatic than in mesenteric arteries, whereas sodium nitroprusside (10(-8)-10(-4) M) produced a similar relaxation in both types of arteries. The inhibitor of nitric oxide synthesis N(w)-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) diminished the relaxation to apelin in mesenteric but not in hepatic arteries. The inhibitor of cyclooxygenase meclofenamate (10(-5) M) did not affect the relaxation provoked by apelin in both types of arteries. Therefore, apelin may produce relaxation in normal human splanchnic arteries, and this relaxation may be mediated in part by nitric oxide without involvement of prostanoids. This relaxation as well as the role of nitric oxide may be decreased in splanchnic arteries from cirrhotic patients.

Endothelium-dependent relaxation of isolated splanchnic arteries from cirrhotic patients: Role of reactive oxygen species.

AIM: To examine the endothelium-dependent relaxation of splanchnic arteries during cirrhosis as well as the role of reactive oxygen species in this relaxation using hepatic arteries from cirrhotic patients undergoing liver transplantation and mesenteric arteries from liver donors. METHODS: Arterial segments 3 mm long were mounted in organ baths for isometric tension recording and precontracted with the thromboxane A(2) analog U46619 (10(-7)-10(-6) M). RESULTS: The relaxation to acetylcholine (10(-8)-10(-4) M), but not to sodium nitroprusside (10(-8)-10(-4) M) was lower in hepatic arteries. The inhibitor of nitric oxide synthesis, N(omega)-nitro-l-arginine methyl ester (l-NAME, 10(-4) M), the inhibitor of cyclooxygenase, meclofenamate (10(-5) M), or l-NAME (10(-4) M) + meclofenamate (10(-5) M) diminished the relaxation to acetylcholine only in mesenteric arteries. l-NAME (10(-4) M) + meclofenamate (10(-5) M) combined with charybdotoxin (10(-7) M) + apamine (10(-6) M) inhibited the relaxation toacetylcholine in both types of arteries, and this inhibition was greater than with l-NAME + meclofenamate. The scavenger of hydrogen peroxide, catalase (1000 U/mL), the superoxide dismutase mimetic, tiron (10(-2) M) or the inhibitor of NAD(P)H oxidase, diphenyleneiodonium (5 x 10(-6) M), but not the inhibitor of superoxide dismutase, diethyldithiocarbamate (10(-3) M) potentiated the acetylcholine-induced relaxation only in hepatic arteries. l-NAME did inhibit the relaxation to acetylcholine in hepatic arteries pretreated with catalase or tiron. CONCLUSIONS: Cirrhosis may decrease endothelial release and/or bioavailability of nitric oxide and prostacyclin in splanchnic arteries, which might be caused partly by increased production of reactive oxygen species.

Goat cerebrovascular reactivity to ADP after ischemia-reperfusion. Role of nitric oxide, prostanoids and reactive oxygen species.

To analyze the cerebrovascular effects of ischemia-reperfusion, cerebrovascular reactivity to ADP was studied after inducing 60-min occlusion followed by 60-min reperfusion of the left middle cerebral artery (MCA) in anesthetized goats. In 12 goats, at the end of reperfusion, left MCA resistance was decreased by 19%, and reactive hyperemia to 5- and 10-s occlusions as well as the cerebral vasodilatation to ADP (0.03-0.3 microg) but not to sodium nitroprusside (0.3-3 microg) was decreased. In 28 animals, killed at the end of reperfusion, segments 3-mm long were obtained from the left (ischemic) and right (control) MCA, prepared for isometric tension recording, and precontracted with the thromboxane A2 analogue U46619. The relaxation to ADP (10(-8) to 10(-5) M) but not to sodium nitroprusside (10(-8) to 10(-4) M) was lower in ischemic arteries. L-NAME (inhibitor of nitric oxide synthesis, 10(-4) M), charybdotoxin (10(-7) M)+apamin (10(-6) M) (blockers of KCa), or catalase (1000 U/ml) reduced the relaxation to ADP only in control arteries. Charybdotoxin+apamin further augmented the L-NAME-induced reduction in the relaxation to ADP in control arteries. The inhibitor of cyclooxygenase meclofenamate (10(-5) M) increased the relaxation to ADP only in ischemic arteries. The superoxide dismutase mimetic tiron (10(-2) M) increased the ADP-induced relaxation only in ischemic arteries. Therefore, it is suggested that ischemia-reperfusion produces cerebrovascular endothelial dysfunction, which may be associated with decreased nitric oxide bioavailability, decreased release of an EDHF, and increased production of vasoconstrictor prostanoids. All these alterations may be related in part with an increased production of superoxide anion.

Effects of antagonists for endothelin ET(A) and ET(B) receptors on coronary endothelial and myocardial function after ischemia-reperfusion in anesthetized goats.

To compare the effects of antagonists for endothelin ET(A) and ET(B) receptors on the action of ischemia-reperfusion on endothelial and myocardial function, 30 min of partial or total occlusion followed by 60 min of reperfusion of the left circumflex coronary artery was induced in anesthetized goats treated with intracoronary administration of saline (vehicle), BQ-123 (endothelin ET(A) receptors antagonist) or BQ-788 (endothelin ET(B) receptors antagonist). During reperfusion after partial occlusion, coronary vascular conductance and left ventricle dP/dt were decreased after saline or BQ-788, and they normalized after BQ-123. In these three groups of animals, the coronary effects of acetylcholine (3-100 ng) and sodium nitroprusside (1-10 microg) during reperfusion were as under control. During reperfusion after total occlusion, coronary vascular conductance and left ventricle dP/dt were decreased after saline, and they normalized after BQ-123 or BQ-788. In these three groups of animals, the coronary effects of acetylcholine but not those of sodium nitroprusside during reperfusion were decreased after saline, and they reversed after BQ-123 or BQ-788. Therefore, selective antagonists of endothelin ET(B) and ET(A) receptors may produce similar protection of coronary vasculature and myocardium against reperfusion after severe ischemia. Selective antagonists of endothelin ET(B) receptors, contrarily to those of endothelin ET(A) receptors, may be ineffective to protect coronary vasculature and myocardium against reperfusion after mild ischemia.

Vasoconstrictor prostanoids may be involved in reduced coronary reactive hyperemia after ischemia-reperfusion in anesthetized goats.

To examine coronary vasodilator reserve after ischemia-reperfusion, reactive hyperemia was determined during reperfusion after partial and total, brief and prolonged ischemia. To this, left circumflex coronary artery flow was electromagnetically measured, and partial (60 min) or total (15 and 60 min) occlusions of this artery were induced, followed in each case by 60-min reperfusion in anesthetized goats untreated and treated with N(W)-nitro-l-arginine methyl ester (l-NAME) or meclofenamate. In untreated and treated animals, coronary flow was decreased during reperfusion after the three types of ischemia. In hyperemic responses to 5- and 10-s coronary occlusions, repayment of debt decreased during reperfusion after the three types of ischemia in untreated animals, and this decrease was not affected by l-NAME. This decrease during reperfusion after partial and total, 60-min ischemia, but not after total, 15-min ischemia, reversed with meclofenamate. Peak hyperemic flow/control flow ratio decreased only during reperfusion after total 60-min occlusion in untreated animals and it was normalized by meclofenamate. These results show that ischemia-reperfusion reduces hyperemic response (vasodilator reserve); this diminution being dependent on duration and severity of ischemia. The hyperemic responses reduction during reperfusion after prolonged ischemia, but not after brief ischemia may be related at least in part to increased production of vasoconstrictor prostanoids.

Enhanced response of pig coronary arteries to endothelin-1 after ischemia-reperfusion. Role of endothelin receptors, nitric oxide and prostanoids.

To analyse the coronary effects of endothelin-1 after ischemia-reperfusion, the left anterior descending coronary artery of anesthetized pigs was subjected to 30-min occlusion followed by 60-min reperfusion. Then, rings distal (ischemic arteries) and proximal (control arteries) to the occlusion were taken from this artery and prepared for isometric tension recording. The sensitivity of the contraction in response to endothelin-1 (3 x 10(-10)-3 x 10(-7) M) and the endothelin ET(B) receptor agonist IRL-1620 (3 x 10(-10)-3 x 10(-7) M) was greater in ischemic vessels. The endothelin ET(A) receptor antagonist BQ-123 (10(-7)-3 x 10(-6) M) decreased the sensitivity of the response to endothelin-1 similarly in ischemic and control arteries. The endothelin ET(B) receptor antagonist BQ-788 (10(-6) M), endothelium removal or the inhibitor of nitric oxide synthesis N(omega)-nitro-L-arginine methyl ester (L-NAME 10(-4) M) potentiated the response to endothelin-1 and IRL-1620 in control arteries only. The cyclooxygenase inhibitor meclofenamate (10(-5) M) augmented the maximal response to endothelin-1 in control arteries, and reduced it in ischemic arteries. In precontracted arteries, IRL-1620 (3 x 10(-11)-3 x 10(-10) M) relaxed control but not ischemic arteries, and L-NAME or meclofenamate abolished this relaxation. Therefore, ischemia-reperfusion increases the coronary vasoconstriction in response to endothelin-1 probably due to impairment of endothelin ET(B) receptor-induced release of nitric oxide and prostacyclin, augmentation of the contractile response to activation of endothelin ET(B) receptors, and increased release of vasoconstrictor prostanoids.

Coronary effects of endothelin-1 and vasopressin during acute hypotension in anesthetized goats.

Coronary effects of endothelin-1 and vasopressin during acute hypotension, and the role of NO and prostanoids in these effects were examined in anesthetized goats. Left circumflex coronary artery flow was measured electromagnetically, and hypotension was induced by constriction of the caudal vena cava in animals non-treated (7 goats) or treated with the inhibitor of NO synthesis N(w)-nitro-L-arginine methyl esther (L-NAME, 5 goats), the cyclooxygenase inhibitor meclofenamate (5 goats) or both drugs (5 goats). Under normotension (22 goats), mean arterial pressure averaged 93 +/- 3 mm Hg and coronary vascular conductance (CVC) 0.37 +/- 0.025 ml/min/mm Hg. Endothelin-1 (0.01-0.3 nmol) and vasopressin (0.03-1 nmol), intracoronarily injected, dose-dependently decreased CVC by up to 56% for endothelin-1 and 40% for vasopressin. During hypotension in every condition tested, mean arterial pressure decreased to approximately 60 mm Hg, and CVC only decreased during hypotension pretreated with L-NAME (23%) or L-NAME + meclofenamate (34%). Under non-treated hypotension, the decreases in CVC by endothelin-1 were augmented approximately 1.5 fold, and those by vasopressin were not modified. This increase in CVR by endothelin-1 was not affected by L-NAME and was reversed by meclofenamate or L-NAME + meclofenamate. The coronary effects of vasopressin were not modified by any of these treatments. Therefore, acute hypotension increases the coronary vasoconstriction in response to endothelin-1 but not to vasopressin. This increased response to endothelin-1 may be related to both inhibition of NO release and release of vasoconstrictor prostanoids.

Mechanisms of the protective effects of urocortin on coronary endothelial function during ischemia-reperfusion in rat isolated hearts.

1 Urocortin is a vasodilator peptide related to corticotrophin-releasing factor, which may protect endothelial function during coronary ischemia-reperfusion (I-R). The aim of this study was to study the mechanisms of this protective effect. 2 Hearts from Sprague-Dawley rats were isolated and perfused at constant flow and then exposed to 15 min global zero-flow ischemia, followed by 15 min reperfusion. The relaxation to acetylcholine (10 nM-10 microM) was recorded after pre-constriction of the coronary vasculature with U46619 (100-300 nM) in ischemic-reperfused or time-control hearts. 3 After I-R, the coronary relaxation to acetylcholine was reduced and this reduction was attenuated by treatment with urocortin (10 pM), administered before ischemia and during reperfusion. 4 This urocortin-induced improvement of the relaxation to acetylcholine was not modified by tetraethylammonium (10 mM), blocker of Ca2+ dependent-potassium channels; glibenclamide (10 microM), blocker of K(ATP) channels; N(w)-nitro-L-arginine methyl ester (L-NAME, 100 microM), blocker of nitric oxide synthesis; or meclofenamate (10 microM), blocker of cyclooxygenase, but it was abolished by chelerythrine (3 microM), blocker of protein kinase C (PKC). 5 These results suggest that urocortin may protect coronary endothelial function during I-R by activation of PKC.

Effect of ischemia duration and nitric oxide on coronary vasoconstriction after ischemia-reperfusion.

The effects of the duration of ischemia on coronary vasoconstriction after ischemia-reperfusion were analysed in rat hearts. After 15, 30 or 45 min of global zero-flow ischemia and 15 min reperfusion, the coronary response to endothelin-1 (10(-10)-10(-7) M) and the thromboxane A2 analogue 9,11-dideoxy-1a,9a-epoxymethanoprostaglandin F2alpha (U46691, 10(-8)-10(-6) M) was recorded. Vasoconstriction induced by endothelin-1 only increased after short 15 min periods of ischemia. In contrast, the vasoconstriction induced by U46619 remained unmodified by short ischemias but was reduced after longer periods of ischemia (30 and 45 min). Inhibition of nitric oxide synthesis with the Nw-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) augmented the vasoconstriction induced by endothelin-1 in non-ischemic hearts, but not following ischemia. Similarly, L-NAME increased the vasoconstriction induced by U46619 to a greater extent in non-ischemic hearts than following ischemia. These results suggest that ischemia-reperfusion inhibits nitric oxide production, causing an increased coronary response to endothelin-1 after brief ischemias. Longer ischemias may non-specifically inhibit coronary vasoconstriction and reduce nitric oxide production.