Japp et al. conducted a study to establish the in vivo vascular actions of apelin in healthy men (n=24). Apelin is the endogenous ligand for the orphan G-protein-coupled receptor, APJ, which is present on endothelial cells, vascular smooth muscle cells, and cardiomyocytes. The authors described the effects of 2 endogenous apelin isoforms, apelin-36 and (Pyr1)apelin-13, on resistance vessels in the forearm vascular bed. Results of this study demonstrated that acute apelin administration in vivo causes nitric oxide (NO)-mediated arterial vasodilatation but does not appear to affect peripheral venous tone. Study findings support previous observations that apelin-APJ signalling has significant effects on cardiovascular homeostasis. However, the authors concluded that this system warrants further clinical investigation to confirm these findings in other vascular beds, such as the coronary circulation.
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