L-Arginine Evokes Relaxations of the Rat Aorta in Both the Presence and Absence of Endothelial Cells

Abstract

Summary: The effect of l-arginine [the substrate for the formation of nitric oxide (NO) in endothelial cells] on the reactivity of isolated vascular preparations was studied. Rings of rat aorta, with or without endothelium, were suspended in organ chambers for the measurement of isometric force. After various incubation periods in physiological salt solution (37°C, 95% O2 and 5% CO2), they were contracted with phenylephrine (10-6M) before the addition of cumulative concentrations of l-arginine. l-Arginine evoked only minor changes in tension in preparations incubated for 0.5 h. However, when the incubation period was longer than 2 h, the amino acid evoked concentration- and time-dependent relaxations in preparations both with and without endothelium. The relaxations evoked by l-arginine were impaired by nitro-l-arginine and methylene blue. Other basic cationic amino acids (d-arginine, l-homoarginine, l-citrulline, l-lysine, and l-ornithine) evoked only small or no relaxations in both types of preparations. These observations demonstrate that l-arginine stereoselectively and specifically relaxes the rat aorta whether or not it contains the endothelium; this response depends on the duration of the prior incubation of the rings in physiological salt solution. The relaxations are impaired by inhibitors of both the formation and the action of NO, demonstrating that the endothelial cells and the vascular smooth muscle of the rat aorta possess an l-arginine-NO pathway(s) associated with relaxation.