PaperAbstract Apelin (AP), an endogenous ligand of the APJ receptor, is involved in the regulation of cardiovascular homeostasis. Regardless the multiple similarities between AP and angiotensin II (Ang II), their roles seem to be different.We studied both the interactions between Apelin 13 (AP13) and Ang II and to what extent, if any, nitric oxide (NO) is involved.The experiments were performed in endothelium-denuded or endothelium-intact rat portal vein in the presence of 10 µM N(G)-nitro L-arginine methyl ester or 10 µM aminoguanidine.AP13 did not modify the isolated rat portal vein tone by itself, but inhibited the Ang II-induced contractions acting mainly by a NO-dependent mechanism. Our results sustain the hypothesis that AP13 could increase the activity of both constitutive and inducible NO synthase on either endothelium intact or endothelium denuded rat portal vein rings.

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