Comparison of the in vivo coronary action of endothelin-1 and vasopressin -: Role of nitric oxide and prostanoids

To compare the coronary effects of endothelin-1 and vasopressin, as well as the role of nitric oxide (NO) and prostanoids in these effects, blood flow in the left circumflex (73 animals) or left anterior descending (19 animals) coronary artery (coronary flow) was electromagnetically measured, and both peptides were intracoronarily injected in anesthetized goats under control conditions and after intravenous administration of the inhibitor of NO synthesis N-w-nitro-L-arginine methyl ester (L-NAME, 47 mg/kg, nine animals) or the inhibitor of cyclooxygenase meclofenamate (6-8 mg/kg, seven animals). In every animal, both endothelin-1 and vasopressin reduced coronary flow in a dose-dependent way, but these reductions by 0.03, 0.1 and 0.3 nmol of endothelin-1 (16%, 33% and 66%, respectively) were significantly higher than those by the equimolar doses of vasopressin (11%, 22% and 35%, respectively). After L-NAME treatment, the reductions of coronary flow by both peptides were augmented, and this augmentation was about two times higher for endothelin-1 than for vasopressin. Meclofenamate treatment did not affect the reductions of coronary flow caused by both peptides. Therefore, we suggest that endothelin-1 is more effective than vasopressin for producing coronary vasoconstriction, but vasopressin also produces remarkable coronary vasoconstriction. Also, it is suggested that NO may play a more relevant role for modulating the coronary vasoconstriction by endothelin-1 than by vasopressin, and that cyclooxygenase products may not be involved in the coronary effects of these two peptides. (C) 2004 Elsevier Inc. All rights reserved.