Antagonism of LTD4-evoked relaxation in canine renal artery and vein.

The goal of this study was to characterize further the manner in which the peptide leukotriene (LT) D4 evokes endothelium-dependent relaxation of the canine renal vein (RV) and artery (RA). The effects of four chemically and structurally dissimilar LT receptor antagonists and pertussis toxin (PTX), on LTD4-evoked relaxation of RV and RA rings, were determined and compared. In the presence of ICI 198,615 (10(-5) M), relaxation of both the RA and RV evoked by LTD4 was markedly attenuated. MK-571 (10(-5) M) altered neither RA nor RV relaxation evoked by LTD4. Relaxation of the RV but not the RA, evoked by LTD4, was attenuated in the presence of LY171,883 (10(-5) M). L649,923 (10(-5) M) solely inhibited LTD4-evoked relaxation of the RA. Pretreatment of vascular rings with PTX (250 ng/ml) for 2 h attenuated the vasomotor relaxation evoked by LTD4 in the RA but not in the RV. These observations suggest that LTD4-evoked relaxation of the RA and RV is dependent on different mechanisms. The endothelium-dependent response produced in the RA apparently involves a PTX-sensitive G protein. It is proposed that multiple signal transduction pathways and perhaps different LTD4 receptors may account for the diverse activity of LTD4.

Leukotrienes C4 and D4 are potent endothelium-dependent relaxing agents in canine splanchnic venous capacitance vessels.

In the present study, the vasomotor effects of the peptide leukotrienes (LTs) LTC4 and LTD4 on isolated canine venous capacitance vessels were evaluated. Both LTs evoked marked concentration-dependent relaxation of norepinephrine-contracted rings of mesenteric and splenic veins and inferior vena cava but had minimal activity in the femoral vein. Relaxation induced by either LT was abolished after physical removal of the vascular endothelium, whereas marked relaxation responses were evoked by glyceryl trinitrate in the same endothelium-denuded rings. The nitric oxide synthase antagonist NG-nitro-L-arginine methyl ester (L-NAME) completely abolished LT-induced mesenteric vein relaxation and unmasked a contractile effect of LTC4. Only partial attenuation of LT-induced relaxation of the inferior vena cava in the presence of L-NAME was observed. In the splenic vein, responses solely to LTC4 were very slightly reduced in the presence of L-NAME. Reduced hemoglobin (10(-6) and 10(-5) M) inhibited LTC4-evoked splenic vein relaxation and, in a concentration of 10(-5) M, inhibited LTD4-evoked relaxation of the splenic vein. On the other hand, methylene blue (10(-6) and 10(-5) M) attenuated splenic vein relaxation produced by both LTs but solely reduced LTC4-evoked inferior vena cava relaxation. Thus, the peptide LTs, the major components of the slow-reacting substance of anaphylaxis, exert a profound endothelium-dependent relaxant effect on venous capacitance vessels, which is only partially dependent on L-arginine and nitric oxide. A role for LT-evoked capacitance venodilation as a mechanism contributing to the reduced venous return and cardiac output associated with systemic anaphylaxis is postulated.

Role of endothelium in responses of isolated hepatic vessels to vasoactive agents.

The role of the endothelium as a participant in the responses to vasoactive agents was evaluated in isolated canine hepatic artery (HA) and portal vein (PV) rings. Endothelial and smooth muscle integrity was determined by pharmacologic responses as well as by histologic examination. Smooth muscle relaxation was expressed as the percent of decrease of norepinephrine-induced isometric contraction. Acetylcholine (ACh)-induced relaxation of the HA was abolished by removing the endothelium or by the addition of either hemoglobin, methylene blue (MB) or Ng-mono-methyl-L-arginine. In addition, relaxation induced by nitroglycerin, but not that induced by prostaglandin E1, was attenuated by MB. These data suggest endothelium-dependency of the relaxation to ACh and mediation of the response by endothelium-derived relaxing factor through activation of guanylate cyclase. In contrast, ACh produced contraction of the PV which was unaffected by removing the endothelium. The calcium ionophore, A23187, on the other hand, produced relaxation of the PV, which was significantly decreased by removing the endothelium. Relaxation of both HA and PV, produced by 2-chloroadenosine (2-C-Ado) was partially attenuated by removing the endothelium. With the endothelium intact, neither hemoglobin, MB, Ng-monomethyl-L-arginine nor indomethacin affected the responses to 2-C-Ado in the HA and PV, suggesting that the responses were not mediated by endothelium-derived relaxing factor or products of guanylate cyclase or cyclooxygenase activity. Nitroglycerin relaxed both vessels in the presence or absence of endothelium, indicating that removal of the endothelium had not affected smooth muscle function.(ABSTRACT TRUNCATED AT 250 WORDS)

LTD4 and bradykinin evoke endothelium-dependent relaxation of the renal vein: dissimilar mechanisms.

This study's goals were to define the vasomotor effects of the peptide leukotriene (LT)D4 on norepinephrine (NE)-contracted isolated rings of canine renal vein (RV) and to compare these influences with those of bradykinin (BK). Canine RV rings were connected to isometric force transducers and bathed in Krebs-Ringer bicarbonate buffer containing indomethacin (10-5M). LTD4 and BK evoked dose-dependent decreases in tone of NE-contracted RV rings that were abolished by physical removal of the endothelium. Relaxation of the RV ring produced by glyceryl trinitrate (GTN) was slightly enhanced or unaltered after endothelium denudation. Reduced human hemoglobin (Hb, 10(-6) M), NG-monomethyl-L-arginine (L-NMMA, 300 microM) and methylene blue (MB, 10(-6) M) had no effect on LTD4-induced venomotor relaxation, whereas they significantly decreased the vasorelaxant effect of BK. In contrast, endothelium-dependent relaxation of renal arterial rings produced in response to both LTD4 and BK was markedly attenuated in the presence of either reduced Hb (10(-6)M) or MB (10(-6) M). MB significantly attenuated venorelaxant responses to GTN (10(-8) to 10(-6) M). The ATP-sensitive K(+)-channel blocker glybenclamide (10(-6)M) inhibited relaxation of the RV induced by cromakalim (5 x 10(-8)M) but had no effect on LTD4-evoked relaxation. These data indicate that endothelium-dependent relaxation of the RV elicited by BK is dependent on "classic" endothelium-derived relaxing factor (EDRF) considered to be nitric oxide (NO) or an unstable nitroso compound that ultimately liberates the NO radical.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of EDRF from canine renal artery by leukotriene D4.

The goal of the present investigation was to determine whether leukotriene D4 (LTD4) was capable of releasing endothelium-derived relaxing factor (EDRF) from perfused renal arterial (RA) segments and to begin to characterize any released mediator. To detect EDRF, a bioassay was used in which a prostaglandin (PG) F2 alpha precontracted, endothelium-denuded coronary artery (CA) ring was superfused either directly or with effluent from a perfused RA segment. Addition of LTD4 or acetylcholine (ACh) to the perfusate proximal to the RA segment resulted in CA ring relaxation, the degree of which was inversely related to transit time. Calculated half-life (t1/2) for the CA relaxing substance released by LTD4 and ACh from the RA segment was 7.5 +/- 1.4 and 7.4 +/- 0.9 s, respectively. Pretreatment of the RA segment with collagenase prevented relaxation of the CA ring evoked by RA effluent in response to either ACh or LTD4 that was administered into the perfusate proximal to the RA segment. Addition of superoxide dismutase (SOD) to the effluent distal to the RA segment markedly enhanced both ACh and LTD4-evoked relaxation of the CA ring, whereas reduced hemoglobin (Hb) virtually abolished these responses. When either LTD4 or ACh was superfused directly over the CA, no change in tone of the bioassay ring was observed. These data indicate that, similar to ACh, LTD4 has the ability to release a labile substance(s), presumably EDRF, from the endothelium-intact RA segment that evokes relaxation of the endothelium-denuded CA ring. Although apparently similar, further studies are required to confirm whether or not the mediator(s) released by LTD4 is identical to that which is released by ACh.

Endothelial-dependent relaxation induced by leukotrienes C4, D4, and E4 in isolated canine arteries.

Leukotriene D4 has been shown to possess the capacity to relax canine superior mesenteric and renal arterial rings in an endothelial-dependent manner. The present study was designed to determine if the remaining peptidoleukotrienes, leukotrienes C4 and E4, share this property. In addition, influences of atropine and of inhibitors of cyclooxygenase and lipoxygenase activities on relaxation produced by leukotriene D4 and acetylcholine were determined to characterize further leukotriene D4-induced relaxation and to compare these properties with those of acetylcholine. Vasomotor tone was measured with isometric force transducers. Following induction of tone with norepinephrine, leukotriene C4 and acetylcholine produced concentration-dependent relaxation of renal and superior mesenteric arterial rings in which the endothelium was intact. Only minimal decreases in tone were produced in response to leukotriene E4. Neither acetylcholine nor leukotriene C4 altered tone after endothelium had been intentionally disrupted. Nitroglycerin relaxed rings both before and after rubbing the endothelium. These results demonstrate that, similar to leukotriene D4, leukotriene C4 possesses the capacity to produce endothelial-dependent relaxation in canine renal and superior mesenteric arteries. Relaxation of the superior mesenteric artery produced in response to acetylcholine, but not leukotriene D4, was inhibited in presence of atropine. Incubation of the rings with meclofenamate had no effect on relaxation induced by either acetylcholine or leukotriene D4. Thus, it appears that endothelial-dependent relaxation induced by leukotriene D4 is neither dependent on muscarinic receptor activation nor related to generation of cyclooxygenase metabolites of arachidonic acid. In contrast, 5,8,11,14-eicosatetraynoic acid and nordihydroguaiaretic acid attenuated relaxation in response to leukotriene D4 and acetylcholine, suggesting that lipoxygenase-derived products may participate in leukotriene D4-induced as well as acetylcholine-induced relaxation.

Relationship between LTD4-induced endothelium-dependent vasomotor relaxation and cGMP.

The objective of the present investigation was to determine whether cyclic GMP (cGMP) participated in endothelium-dependent leukotriene (LT) D4-induced relaxation of canine superior mesenteric artery. All experiments were performed with endothelium-intact arterial rings, and tone was measured with isometric force displacement transducers. After tone had been induced with norepinephrine, LTD4 acetylcholine (ACh), nitroglycerin (GTN) and isoproterenol (ISOP), each produced concentration-dependent vasomotor relaxation. Because contractile responses produced by norepinephrine were enhanced in presence of methylene blue, the concentration of norepinephrine was reduced in order to induce tone that was equivalent to control. After this adjustment, incubation of the rings with methylene blue attenuated relaxation produced by LTD4, ACh and GTN, whereas ISOP-induced decreases in tone were unaltered. In addition, results of a separate series of experiments showed that cGMP levels in the arterial rings were enhanced at the time of peak relaxation produced in response to LTD4, ACh and GTN. In contrast to these observations, ISOP-induced relaxation was not associated with a change in cGMP concentration. When taken together, these results suggest that cGMP serves as a participant in endothelium-dependent relaxation produced by both LTD4 and ACh, as well as endothelium-independent relaxation produced by GTN.

Leukotriene D4 relaxes canine renal and superior mesenteric arteries.

To characterize the influences of leukotriene D4 on regional vascular smooth muscle, effects of leukotriene D4 on vasomotor tone of canine renal and superior mesenteric arterial rings were determined. Vascular smooth muscle tone was measured with isometric force transducers. After tone had been induced with norepinephrine, leukotriene D4, in concentrations of 10(-8) M to 10(-7) M, produced dose-dependent relaxation of renal and superior mesenteric arterial rings. Leukotriene D4-induced relaxation was observed only in those ring preparations in which care had been taken to avoid damaging the luminal surface. Acetylcholine (10(-7) M) also decreased tone in these same ring segments. Neither acetylcholine nor leukotriene D4 altered tone of arterial rings after the endothelium had been intentionally disrupted by rubbing with a cotton-tipped applicator. Nitroglycerin (10(-6) M) relaxed rings both before and after rubbing the intimal surface. These results demonstrate that leukotriene D4 possesses the capacity to relax canine superior mesenteric and renal arterial rings in an endothelial-dependent manner. Because relaxation of renal and superior mesenteric arterial rings in response to leukotriene D4 was not altered after incubation with indomethacin (10(-5) M), the observed endothelial-dependent relaxation induced by leukotriene D4 did not appear to be related to release of a cyclooxygenase metabolite(s). In contrast, FPL 55712 (10(-5) M) attenuated the relaxation produced by leukotriene D4, suggesting that this response was a receptor-linked consequence.

Action of arachidonic acid in ureteral-ligated kidney of the anesthetized canine: possible lipoxygenase activity.

In anesthetized dogs 48 h after unilateral ureteral ligation, intra-arterial injection of arachidonic acid produced a transient increase followed by a prolonged decrease of resistance in the ureteral-ligated kidney; whereas, in the control kidney, only the prolonged decrease in resistance was observed in response to arachidonate. Indomethacin blocked not only the arachidonate-induced renal efflux of both immunoreactive 6-keto-prostaglandin F1 alpha and thromboxane B2 but also vasodilation in both kidneys. In contrast, the initial vasoconstriction in the obstructed kidney was not affected by pretreatment with the cyclo-oxygenase inhibitor. Infusion of 5,8,11,14-eicosatetraynoic acid, an inhibitor of lipoxygenase activity, into the ureteral-ligated kidney after indomethacin markedly reduced the initial vasoconstrictor response to arachidonate. These data demonstrate that vascular reactivity to arachidonic acid is altered in the ureteral-obstructed kidney and are consistent with the hypothesis that formation of lipoxygenase as well as cyclooxygenase derivatives may participate in the hemodynamic responses to arachidonic acid in this pathophysiologic model.

Divergent influences of leukotrienes C4, D4, and E4 on mesenteric and renal blood flow.

Influences of leukotrienes C4 (LTC4), D4 (LTD4), and E4 (LTE4) on mesenteric and renal blood flow were investigated in the anesthetized dog. Blood flow was measured with noncannulating electromagnetic flow probes, and all agonists were injected as a bolus close arterially. When injected into the superior mesenteric artery, LTC4 (0.1-3.0 ng), LTD4 (0.1-1.0 ng), and LTE4 (1-30 ng) produced dose-dependent decreases in blood flow in absence of a change in mean arterial pressure. When compared with intestinal vasoconstrictor responses caused by angiotension II, which was most active, and norepinephrine, which was least active, the leukotrienes were intermediate between these two well-known vasoactive hormones. LTD4 was more active than LTC4, and both were considerably more active than LTE4. In contrast to the intestine, injection of leukotrienes (1,000 ng) into the kidney resulted in little to no change in renal blood flow or mean arterial pressure, but mesenteric flow decreased 10-15 s later. Administration of indomethacin (5 mg/kg iv) did not alter mesenteric vasoconstrictor responses produced by LTD4. However, mesenteric vasoconstrictor responses to prostaglandin (PG)D2 were reduced after indomethacin, whereas renal vasodilation caused by PGD2 was unaffected. These results demonstrate that LTC4, LTD4, and LTE4 differentially affect blood flow in the intestine and kidney and suggest that if circulating levels of leukotrienes are increased, blood flow would be expected to be diverted away from the intestine. These data are thus compatible with the hypothesis that leukotrienes may participate in regulation of peripheral regional blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of prostaglandins on vasoconstrictor responses in the hindquarters vascular bed of the cat.

The effects of prostaglandins (PG), A1, A2, B2, E1, 6-keto-E1, F2 alpha and indomethacin on vascular resistance and vasoconstrictor responses were investigated in the feline hindquarters vascular bed under conditions of controlled flow so that changes in perfusion pressure directly reflect changes in vascular resistance. Infusion of PGE1, PGE2 and 6-keto-PGE1 (3 microgram/min) into the abdominal aorta significantly dilated the hindquarters vascular bed and inhibited vasoconstrictor responses to sympathetic nerve stimulation and intra-arterial injections of angiotensin, whereas hindquarters vasoconstrictor responses to tyramine and exogenous norepinephrine were unaffected. Infusion of PGA1, A2, B2 and F2 alpha at a similar rate produced transient changes in hindquarters vascular resistance and did not consistently alter vasoconstrictor responses to sympathetic nerve stimulation, angiotensin, norepinephrine and tyramine. Indomethacin in a dose which greatly attenuates the response to intravenous administration of arachidonic acid enhanced responses to nerve stimulation and norepinephrine. In addition, indomethacin had little or no effect on hindquarters perfusion pressure and systemic arterial pressure. These data suggest that E series prostaglandins possess the ability to modulate the actions of the sympathetic nervous system and angiotensin in the feline hindquarters vascular bed. In addition, these data suggest that PGEs, upon enzymatic conversion and dehydration to A and B series prostaglandins, lose their ability to consistently affect vasoconstrictor responses. Experiments with indomethacin further suggest that locally formed prostaglandins do modulate the effects of the sympathetic nervous system of the feline hindquarters.

The influence of indomethacin on vasodilator responses to bradykinin and nitroglycerin in the cat.

The effects of indomethacin, a cyclooxygenase inhibitor, on vasodilator responses to bradykinin and nitroglycerin were investigated in the peripheral vascular bed of the anesthetized cat. Intra-arterial injections of bradykinin and nitroglycerin elicited dose-related decreases in mesenteric and hindquarters vascular resistance. Mesenteric vasodilator responses to nitroglycerin in absolute units were unchanged 30 min after administration of indomethacin whereas responses to bradykinin expressed as an absolute mm Hg decrease in perfusion pressure were increased. Indomethacin was also without effect on vasodilator responses to lower doses of nitroglycerin whereas responses to higher doses of nitroglycerin and bradykinin in absolute units were enhanced in the hindquarters vascular bed. Indomethacin increased vascular resistance in the mesenteric and hindquarters vascular beds and decreased systemic vasodepressor responses to the prostaglandin precursor, arachidonic acid. When the increase in (initial value) vascular resistance was taken into account by expressing vasodilator responses on a percent decrease basis, indomethacin only enhanced the vasodilator response to the highest does of bradykinin studies. Result of the present study suggest that products in the cyclooxygenase pathway may serve to maintain the peripheral vascular bed of the cat in a dilated state but that these metabolites do not mediate vasodilator responses to bradykinin. The present data further suggest that products in the cyclooxygenase pathway may play a minor role in modulating the dilator effects of bradykinin in the mesenteric and hindquarters vascular beds of the cat.

Inhibition of vasoconstrictor responses by 6-keto-PGE1 in the feline mesenteric vascular bed.

The effects of 6-keto-PGE1 on vascular resistance and vascular responses to sympathetic nerve stimulation and vasoconstrictor hormones were investigated in the feline mesenteric vascular bed. Infusions of 6-keto-PGE1 into the superior mesenteric artery dilated the mesenteric vascular bed and markedly inhibited vasoconstrictor responses to sympathetic nerve stimulation, norepinephrine and angiotensin II. The effects of 6-keto-PGE1 and PGE1 on vascular resistance and vasoconstrictor responses were quite similar and both substances inhibited responses to nerve stimulation and pressor hormones in a reversible manner. Responses to nerve stimulation, norepinephrine and angiotensin II were inhibited to a similar extent during infusion of 6-keto-PGE1 and PGE1. Results of these studies suggest that 6-keto-PGE1, a newly identified prostaglandin metabolite, and PGE1 possess the ability to inhibit the vasoconstrictor effects of sympathetic nerve stimulation and pressor hormones by a non-specific action on vascular smooth muscle in the feline small intestine.

Inhibition of vasoconstrictor responses by prostacyclin (PGI2) in the feline mesenteric vascular bed.

The effects of infusion of prostacyclin, PGI2, on vasoconstrictor responses to sympathetic nerve stimulation, norepinephrine and angiotensin II were investigated in the mesenteric vascular bed of the cat. Stimulation of the sympathetic nerves and intra-arterial injections of norepinephrine and angiotensin increased mesenteric perfusion pressure in a frequency and dose-dependent manner. Responses to nerve stimulation and pressor hormones were reproducible and not altered by infusions of the Tris vehicle for PGI2 or the PGI2 breakdown product, 6-keto-PGF1 alpha. Infusions of PGI2, 1 and 0.3 micrograms/min, decreased mesenteric arterial perfusion pressure and, at the higher infusion rate, markedly reduced responses to nerve stimulation, norepinephrine and angiotensin. At the lower infusion rate PGI2 caused small but significant reductions in responses to norepinephrine and nerve stimulation but did not alter responses to angiotensin. Results of these studies demonstrate that PGI2 possesses the ability to inhibit vasoconstrictor responses in the feline intestinal vascular bed and suggest that this effect is postjunctional.

Cardiovascular actions of prostacyclin (PGI2) in the cat.

The cardiovascular actions of the newly discovered bicyclic prostaglandin, prostacyclin, or PGI2, were compared with those of PGE1 in the anesthetized cat. PGI2 decreased systemic arterial pressure, increased cardiac output and decreased systemic vascular resistance. The decreases in systemic vascular resistance were similar when PGI2 was injected into the left or right atrium, suggesting that prostacyclin is not inactivated in the feline pulmonary vascular bed. PGE1 also decreased systemic arterial pressure and increased cardiac output; however, left atrial administration of this substance produced greater reductions in systemic vascular resistance than right atrial injections, suggesting that PGE1 is inactivated in the feline lung. PGI2 also caused dose-related decreases in perfusion pressure in the renal, hindquarters and mesenteric vascular beds and had the greatest vasodilator activity in the mesenteric vascular bed. PGE1 decreased perfusion pressure in the 3 regional beds, and the overall dilator effects of PGI2 and PGE1 in the peripheral circulation were quite smiliar. The present data show that PGI2 is a potent peripheral vasodilator in the cat and since this substance is not inactivated in the lung, it could serve as a circulating hormone in this species.

Evidence for separate PGD2 and PGF2 alpha receptors in the canine mesenteric vascular bed.

Potential interactions between PGD2 and PGF2 alpha in the mesenteric and renal vascular beds were investigated in the anesthetized dog. Regional blood flows were measured with electromagnetic flow probes. PGD2, PGF2 alpha and Norepinephrine (NE) were injected as a bolus directly into the appropriate artery, and responses to these agents were obtained before, during and after infusion of either PGD2 or PGF2 alpha into the left ventricle. In each case, the infused prostaglandin caused vascular effects of its own. Left ventricular infusion of PGD2 reduced responses to local injections of PGD2 in the intestine, and a similar effect was observed for PGF2 alpha, suggesting significant receptor or receptor-like interactions for each of the prostanoids. However, systemic infusion of prostaglandin F2 alpha (20--100 ng/kg/min) had no effect on renal or mesenteric vascular responses to local injection of prostaglandin D2. Similarly, PGD2 administration (100 ng/kg/min) did not affect responses to PGF2 alpha in the intestine. The present results therefore suggest that these prostaglandins, i.e., D2 and F2 alpha, act through separate receptors in the mesenteric and renal vascular beds. In addition, increased prostaglandin F2 alpha levels produced by infusion of F2 alpha reduced mesenteric but not renal blood flow, suggesting that redistribution of cardiac output might participate in side effects often observed with clinical use of this prostaglandin, such as nausea and abdominal pain.

Pulmonary and systemic vasodilator effects of the newly discovered prostaglandin, PGI2.

The effects of the newly discovered bicyclic prostaglandin, prostacyclin (PGI2), on the pulmonary and systemic vascular beds were investigated in the anesthetized dog. PGI2 decreased systemic and pulmonary arterial pressures in a dose-related manner when injected into the vena cava in doses of 1--30 microgram. Since left ventricular end-diastolic, left atrial, and right atrial pressures were unchanged, and since cardiac output was increased or unchanged, pulmonary and systemic vascular resistances were decreased. PGI2 was 10 times more potent than prostaglandins E1 or E2 in decreasing aortic pressure when injected intravenously, and the effects of PGI2 on the systemic vascular bed were similar when injected into the vena cava or the left atrium. These data indicate that inactivation of PGI2 is minimal in the lung. The stable prostacyclin metabolite, 6-keto-PGF1alpha, had little hemodynamic effects, suggesting that responses to PGI2 were not due to formation of this metabolite. PGI2 produced dose-dependent increases in blood flow in the mesenteric and renal vascular beds. These data demonstrate that PGI2 has marked vasodilator activity in the pulmonary and systemic vascular beds and suggest that prostacyclin is the only known metabolite of arachidonic acid that dilates the pulmonary and systemic circulations.