Endothelial L-arginine pathway and regional cerebral arterial reactivity to vasopressin

Experiments were designed to characterize the mechanism of vasopressin action in small arteries of brain stem and cerebrum and to determine the role of L-arginine pathway in reactivity of these vessels to vasopressin. Secondary branches of canine basilar arteries (425 ± 63 μm ID, n = 6) and middle cerebral arteries (466 ± 30 μm ID, n = 6) were dissected and mounted on glass microcannulas in organ chambers. Changes in intraluminal diameter of the pressurized arteries were measured using a video dimension analyzer. Vasopressin caused endothelium-dependent relaxation in the brain stem arteries [-log half-maximal effective concentration (EC₅₀) = 9.2 ± 0.4, n = 5] but not in the branches of middle cerebral-arteries. In contrast, bradykinin caused identical endothelium-dependent relaxations in arteries of both regions (-log EC₅₀ = 8.0 ± 0.2, n = 5, and 7.7 ± 0.1, n = 4 for brain stem and cerebrum, respectively). Relaxations to vasopressin (but not to bradykinin) were reduced in the presence of V₁-vasopressinergic antagonist [1-(β-mercapto-β-cyclopentamethylenepropionic acid),2-(O- methyl)tyrosine]arginine vasopressin [d(CH₂)₅-Tyr(Me)AVP;10^-7 M], pertussin toxin (100 ng/ml), and N(G)-monomethyl-L-arginine (L-NMMA; 10^-4 M). The inhibitory effect of L-NMMA was prevented by L-arginine (3 x 10^-4 M) but not D-arginine (3 x 10^-4 M). These studies suggest that vasopressin causes endothelium-dependent relaxation in canine brain stem arteries. The effect of the neuropeptide appears to be mediated by activation of endothelial V₁-vasopressinergic receptors coupled to nitric oxide synthase. This signal transduction pathway is not functional in endothelial cells of branches of middle cerebral arteries.