Coronary reactivity to endothelin-1 during partial ischemia and reperfusion in anesthetized goats. Role of nitric oxide and prostanoids

Altered reactivity of tertiary mesenteric arteries following acute myocardial ischemia

BACKGROUND

It is unknown if cardiac ischemia has any deleterious effect on the contractile properties of nonischemic, peripheral vascular beds. Thus, the objective of the present study was to determine whether acute myocardial ischemia results in peripheral vascular dysfunction.

METHODS AND RESULTS

This study characterized force maintenance and the sensitivity to acetylcholine (ACh)-mediated smooth muscle (SM) relaxation of tertiary (3rd) mesenteric arteries from Sprague-Dawley rats following 30 min of myocardial ischemia. Both the phosphorylation of nonmuscle (NM) light chain (LC) and SM-LCs as well as the expression of myosin phosphatase targeting subunit 1 (MYPT1) were also determined. Our data demonstrate that acute myocardial ischemia resulted in vascular dysfunction of 3rd mesenteric vessels, characterized by decreases in force maintenance, ACh- and cGMP-mediated SM relaxation, the phosphorylation of NM-LCs and SM-LCs, and MYPT1 expression. Ischemia was also associated with an increase in protein polyubiquitination, suggesting that during ischemia MYPT1 is targeted for degradation or proteolysis.

CONCLUSION

Acute myocardial ischemia produces peripheral vascular dysfunction; the changes in LC phosphorylation and MYPT1 expression result in a decrease in both tone and the sensitivity to NO-mediated SM relaxation of the peripheral vasculature.

Effects of antagonists for endothelin ETA and ETB 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.

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.

Changes of tissue endothelin-1 and nitric oxide synthase in a sheep model of large intestinal obstruction

Large intestinal obstruction (LIO) in farm animals can cause a ischaemic necrosis of intestinal tissue, eventually leading to death. The roles of endothelin-1 (ET-1) and nitric oxide (NO) are not well understood in the process of LIO, but evidence suggests that endothelial-derived mediators may participate. In the present study, ET-1 concentration and total nitric oxide synthase (NOS) activity were measured in heart, liver, pancreas, lung and kidney in a model of LIO in sheep. Our data demonstrated that ET-1 concentration and NOS activity were altered, with significant increases of ET-1 in heart, lung and kidney and of NOS activity in pancreas and kidney, but a marked decline of NOS activity in liver (p < 0.05). It is postulated that these alterations in NOS activity and ET-1 concentration may contribute to the progressive loss of organ function, and finally lead to death in LIO in sheep.

Vasopressin effects on the coronary circulation after a short ischemia in anesthetized goats

To examine the coronary effects of arginine-vasopressin during reperfusion after a short ischemia, left circumflex coronary artery flow was electromagnetically measured, and 15 min total occlusion of this artery followed by reperfusion was induced in anesthetized goats (five nontreated, five treated with the inhibitor of nitric oxide synthesis Nomega-nitro-L-arginine methyl ester (L-NAME) and five treated with the inhibitor of cyclooxygenase meclofenamate). The vasoactive drugs and L-NAME were intracoronarily injected, and meclofenamate by i.v. route. At 60 min of reperfusion, coronary vascular conductance was not changed significantly in nontreated and was decreased by 35% (P<0.01) in L-NAME-treated and by 30% (P<0.01) in meclofenamate-treated animals. During reperfusion, the coronary vasodilatation with acetylcholine (3-100 ng) and sodium nitroprusside (1-10 microg) was not altered in nontreated animals, and the vasodilatation with acetylcholine but not with sodium nitroprusside was partially decreased in L-NAME--but not in meclofenamate-treated animals. The vasoconstriction in response to arginine-vasopressin (0.03-0.3 microg) was increased during reperfusion in nontreated, was not changed in L-NAME-treated and was decreased in meclofenamate-treated animals. Therefore, it is suggested that during reperfusion after a short ischemia: (1) the coronary vasodilator reserve is preserved; (2) the coronary vasodilatation with acetylcholine is also preserved, but in this vasodilatation, the role of nitric oxide may be attenuated and prostanoids may be not involved; and (3) the coronary vasoconstriction with arginine-vasopressin is increased, probably due to both attenuation of the modulatory role of nitric oxide and the release of vasoconstrictor prostanoids.

Coronary smooth muscle reactivity to muscarinic stimulation after ischemia-reperfusion in porcine myocardial infarction

This study tested whether ischemia-reperfusion alters coronary smooth muscle reactivity to vasoconstrictor stimuli such as those elicited by an adventitial stimulation with methacholine. In vitro studies were performed to assess the reactivity of endothelium-denuded infarct-related coronary arteries to methacholine (n = 18). In addition, the vasoconstrictor effects of adventitial application of methacholine to left anterior descending (LAD) coronary artery was assessed in vivo in pigs submitted to 2 h of LAD occlusion followed by reperfusion (n = 12), LAD deendothelization (n = 11), or a sham operation (n = 6). Endothelial-dependent vasodilator capacity of infarct-related LAD was assessed by intracoronary injection of bradykinin (n = 13). In vitro, smooth muscle reactivity to methacholine was unaffected by ischemia-reperfusion. In vivo, baseline methacholine administration induced a transient and reversible drop in coronary blood flow (9.6 +/- 4.6 to 1.9 +/- 2.6 ml/min, P < 0.01), accompanied by severe left ventricular dysfunction. After ischemia-reperfusion, methacholine induced a prolonged and severe coronary blood flow drop (9.7 +/- 7.0 to 3.4 +/- 3.9 ml/min), with a significant delay in recovery (P < 0.001). Endothelial denudation mimics in part the effects of methacholine after ischemia-reperfusion, and intracoronary bradykinin confirmed the existence of endothelial dysfunction. Infarct-related epicardial coronary artery shows a delayed recovery after vasoconstrictor stimuli, because of appropriate smooth muscle reactivity and impairment of endothelial-dependent vasodilator capacity.