SARMESIN IS A PARTIAL AGONIST OF ANGIOTENSIN-II RECEPTORS IN RABBIT, BUT NOT IN RAT, AORTIC RINGS

Sarmesin, [Sar1,Tyr(Me)4]angiotensinII], has been reported to be a competitive angiotensin II (AII) receptor antagonist in rat smooth muscle preparations (Scanlon et al., (1984), Life Science 34, 317-321). In the present study, sarmesin displaced AII from its binding sites in rat aortic smooth muscle cells and in a rabbit aorta membrane preparation (IC50 5 and 6 nM resp.; Ki 4.1 and 5.3 resp.) In rabbit aortic rings, sarmesin (0.003-3 μM) produced concentration-dependent contractions (ED50 89 nM) and this effect was inhibited by saralasin. No contraction was observed in the rat aorta up to 100 μM. In rabbit aortic rings, sarmesin, at the same concentrations that produced contraction, inhibited contractions induced by AII in a competitive manner (pA2 7,26). These results indicate that, in rabbit aortic rings sarmesin is a partial agonist of AII receptors. © 1990.