Nitric oxide mediates inhibitory effect of losartan on angiotensin-induced contractions in hamster but not rat aorta

Abstract

We investigated a possible contribution of nitric oxide (NO) and prostaglandins to the inhibitory effect of losartan on contractions to Ang I (10^-6 M) and Ang II (10 ^-7 M) with or without L-NAME (10^-4 M) or indomethacin (10 ^-5 M) in the aorta of WKY, SHR and hamster (n=7 each). Rings of thoracic aorta (2-mm long) were placed in a myograph (5 ml). Endothelium-dependent vasodilations were evaluated with acetylcholine (10^-8 ~ 10 ^-6 M). After a 45-minute incubation with L-NAME under a resting tension of 2 g, only hamster aorta contracted (pvs 99% inhibition, p<0.05). Indomethacin did not alter the effect of losartan in any vessels. Our results suggest that the presence of NO, particularly a basal secretion of NO, is necessary for the full expression of the inhibitory effect of losartan in the hamster, but not in WKY or SHR, aorta. Unlike NO, prostaglandins do not appear to play a role in the effect of losartan.