Endothelium dependent vascular relaxation by arginine containing polypeptides

The vascular endothelium appears obligatory for the expression of the vasodilating property of most polypeptides. A number of polypeptides were studied on the rat aortic ring preparation which was pre-contracted with phenylephrine and only basic polypeptides containing one or more arginine residues elicited relaxation which was endothelium dependent. These peptides included melittin and poly-L-Arg. The basic polypeptide poly-L-Lys also elicited endothelium dependent relaxation, but to a lesser extent than arginine containing polypeptides. Two basic polypeptides, apamin and mastoparan do not promote endothelium dependent relaxation. The former contains arginine between disulfide bonds and in the latter arginine is absent. Basic amino acids and dipeptides which contain arginine, and also polyamines did not elicit relaxation even at high concentrations (10(-3) M). The relaxation elicited by melittin, poly-L-Arg and poly-L-Lys was inhibited by ETYA, NDGA, p-bromophenacyl bromide and not by indomethacin. Methylene blue, an inhibitor of soluble guanylate cyclase, also abolished the relaxation. We suggest that arginine containing peptides may relax vascular smooth muscle by acting directly on the vascular smooth muscle (eg: atriopeptins) and/or or by eliciting release of a relaxing factor(s) from the endothelium.