Melatonin inhibits nitric oxide production by microvascular endothelial cells in vivo and in vitro

Abstract

Background and purpose: We have previously shown that melatonin inhibits bradykinin-induced NO production by endothelial cells in vitro. The purpose of this investigation was to extend this observation to an in vivo condition and to explore the mechanism of action of melatonin. Experimental approach: RT-PCR assays were performed with rat cultured endothelial cells. The putative effect of melatonin upon arteriolar tone was investigated by intravital microscopy while NO production by endothelial cells in vitro was assayed by fluorimetry, and intracellular Ca 2 þ measurements were assayed by confocal microscopy. Key results: No expression of the mRNA for the melatonin synthesizing enzymes, arylalkylamine N-acetyltransferase and hydroxyindole-O-methyltransferase, or for the melatonin MT 2 receptor was detected in microvascular endothelial cells. Melatonin fully inhibited L-NAME-sensitive bradykinin-induced vasodilation and also inhibited NO production induced by histamine, carbachol and 2-methylthio ATP, but did not inhibit NO production induced by ATP or a, b-methylene ATP. None of its inhibitory effects was prevented by the melatonin receptor antagonist, luzindole. In nominally Ca 2 þ -free solution, melatonin reduced intracellular Ca 2 þ mobilization induced by bradykinin (40%) and 2-methylthio ATP (62%) but not Ca 2 þ mobilization induced by ATP. Conclusions and implications:We have confirmed that melatonin inhibited NO production both in vivo and in vitro. In addition, the melatonin effect was selective for some G protein-coupled receptors and most probably reflects an inhibition of Ca 2 þ mobilization from intracellular stores.

Melatonin receptors mediate improvements of liver function but not of hepatic perfusion and integrity after hemorrhagic shock in rats*

“…Our data are supported by the observation that melatonin inhibits expression of nitric oxide synthase in different settings (24,25). Furthermore, melatonin was recently reported to attenuate nitric oxide production by endothelial cells in vivo (26). Therefore, our results allow the conclusion that melatonin improves hepatic perfusion by presinusoidal adaptations.…”

MT2 Receptors Mediate the Inhibitory Effects of Melatonin on Nitric Oxide-Induced Relaxation of Porcine Isolated Coronary Arteries

“…One potential site of action for melatonin could be endothelial NO synthase (eNOS). Indeed, melatonin inhibits NO production in rat microvascular endothelial cells (Silva et al, 2007), although this effect is not observed in larger arteries of the rat (Monroe and Watts, 1998). Although an effect of melatonin on eNOS in porcine coronary arteries cannot be ruled out, the observation that melatonin also inhibits relaxation induced by SNP, which is independent of eNOS (Kowaluk et al, 1992), suggests a site of action for melatonin other than, or in addition to, eNOS.…”

Purinergic Signaling and Blood Vessels in Health and Disease

“…a,b-MeATP, presumably acting via P2X 1 or P2X 3 receptors, caused production of NO by microvascular endothelial cells from rat cremaster muscle; unlike the actions of 2-methylthio ATP (2-MeSATP) at coexpressed endothelial P2Y 1 receptors, NO production by a,b-meATP was unaffected by melatonin, indicating distinct sites of action (Silva et al, 2007). It was reported that P2X 1 receptors are expressed in the endothelium of rat mesenteric arteries and that their activation leads to vasodilation largely via EDHF (Harrington and Mitchell, 2004).…”