British Journal of Pharmacology 2012-05-01

L-tryptophan ethyl ester dilates small mesenteric arteries by inhibition of voltage-operated calcium channels in smooth muscle.

Ashok Jadhav, Wenbin Liang, John Balsevich, Guillaume Bastin, Jeff Kroetsch, Scott Heximer, Peter H Backx, Venkat Gopalakrishnan

Index: Br. J. Pharmacol. 166(1) , 232-42, (2012)

Full Text: HTML

Abstract

L-tryptophan (L-W) is a precursor of the vasoconstrictor, 5-HT. However, acute administration of L-W ethyl ester (L-Wee) lowered blood pressure. The mechanism of action is unknown. This study compares the vascular effects of L-W and L-Wee in intact animals, isolated aortic rings, small mesenteric arteries (MA) and explores possible mechanisms by studies in vascular smooth muscle cells (VSMC) of MA.Effects of L-W or L-Wee (5-50 mg kg(-1) , i.v.) on mean arterial pressure (MAP) and heart rate (HR) were determined in male Sprague-Dawley rats. The effects of L-W and L-Wee on basal tone and of phenylephrine- or KCl-induced contractions of aortic and MA rings were assessed. Effects of L-Wee and L-W on voltage-operated calcium channels (VOCC) of VSMC of MA were also examined in patch-clamp studies.Administration of L-Wee, but not L-W, evoked a rapid and transient dose-dependent decrease in MAP and HR. While both agents failed to affect basal tone, L-Wee decreased, concentration-dependently, (I(max) > 98%) tension responses to phenylephrine and KCl in an endothelium-independent manner in aorta (IC(50) 2 mM) and MA (IC(50) 17 µM). L-Wee evoked concentration-dependent inhibition of VOCC currents (IC(50) 12 µM; I(max) 90%) in VSMC of MA.Esterified L-W (L-Wee), but not L-W, preferentially relaxed resistance vessels rather than conduit vessels. These effects were associated with blockade of VOCC by L-Wee. Our findings suggest that the falls in MAP and HR induced by L-Wee were due to blockade of VOCC by L-Wee.© 2011 The Authors. British Journal of Pharmacology © 2011 The British Pharmacological Society.