Pyr1-apelin-13 is a potent endothelium dependent vasodilator in human artery opposing vasoconstriction via APJ receptors

Matthias J. Kleinz, Janet J Maguire & Anthony P. Davenport, Clinical Pharmacology Unit, University of Cambridge, Level 6, ACCI, Box 110, Addenbrooke’s Hospital, Cambridge CB2 2QQ.

Apelin peptides are a group of endogenous ligands for the novel receptor APJ with vascular actions in rat and human, and pyr1-apelin-13 was described as a vasoconstrictor in endothelium-denuded isolated human vein (Katugampola et al., 2001) . To investigate vasoactive properties of different apelin peptides in man we compared the vasoconstrictor action of pyr1-apelin-13 and apelin-36 in endothelium denuded human saphenous vein. Recently we have detected APJ on human vascular smooth muscle cells and endothelial cells. Based on this distribution and the hypotensive effects of apelin observed in rats, we hypothesised, that in man, apelins may act as endothelium-dependent vasodilators and tested this hypothesis in isolated internal mammary artery.

Saphenous veins from 20 patients (mean age 68.20±2.42years) were obtained with ethical approval. Endothelium denuded rings were set up for isometric tension recordings in oxygenated Krebs’ solution (37 °C) and used to construct concentration response curves to pyr1-apelin-13 and apelin-36 (10pM-300nM). Vasoconstrictor responses were expressed as percentage of a terminal KCl (0.1M) response and PD2 and Emax values for both peptides were compared using students unpaired two-tailed t-test (p<0.05 significant). In rings of left internal mammary artery from nine patients (mean age 69.22±2.11years) presence of functional endothelium was confirmed showing >50% reversal of phenylephrine (1µM) preconstriction by 1µM acetylcholine. Vessels were preconstricted with 10nM ET-1 and cumulative concentration response curves were constructed to pyr1-apelin-13 (10pM-300nM). Experiments were terminated by testing tissue responses to ANP (0.1nM) and SNAP (0.1µM). Vasodilator responses were expressed as percentage reversal of ET-1 constriction.

Pyr1-apelin-13 and apelin-36 constricted endothelium denuded saphenous vein with comparable potency (pD2 8.84±0.47(mean±s.e.mean) vs. 8.16±0.57, p=0.42). The Emax for pyr1-apelin-13 however was significantly higher than for apelin-36 (29.70±4.65% vs. 11.91±5.10%, p= 0.04). pyr1-apelin-13 reversed ET-1 induced vasoconstriction of internal mammary artery with a pD2 value of 8.76±0.15 and an Emax of 38.84±2.46%. In an endothelium denuded vessel ring pyr1-apelin-13 had no vasodilator effect.

Our results showing higher efficacy of pyr1-apelin-13 in saphenous vein compared to apelin-36 suggests that short apelin peptides with pyroglutamate modification have stronger vasoactive properties in humans than longer peptide forms and therefore may represent the mature, biologically active peptide form. In agreement with endothelium dependent in vivo hypotensive actions of apelin peptides in the rat (Tatemoto et al., 2001) and the reported presence of APJ on human vascular endothelial cells we show potent endothelium dependent vasodilator actions for pyr1-apelin-13 in isolated human mammary artery with comparable potency to that of other established vasodilator peptides such as ANP and CGRP (Wiley et al., 2002) . Thus apelin peptides present in endothelial cells (Kleinz et al., 2005) may play an important role in maintaining physiological vascular tone in man.

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Wiley, K.E. et al. (2002), Br J Pharmacol, 136, 1146-52.