Comparison of atriopeptins II and III, VIP andβ2‐‐adrenoceptor‐evoked relaxations of the two layers of smooth muscle in the rat portal vein

Publisher Website
Google Scholar
Abstract
Comparison of atriopeptins II and III, VIP andβ2‐‐adrenoceptor‐evoked relaxations in the two layers of smooth muscle in the rat portal vein.Acta Physiol Stand130, 593–599. Received II November 1986, Accepted 26 February 1987. ISSN 0001–6772. Department of Physiology, University of Bergen, Norway.The relative importance of vascular relaxations induced by atriopeptins (AP), theβ‐adrenoceptor agonist isoprenaline and of the neuropeptide VIP was studiedin uitroon circular and longitudinal preparations of the rat portal vein. Two members of the rat atriopeptins (AP II and III) were equipotent with respect to relaxation of the spontaneously contracting outer, longitudinal layer and of theα1‐‐contracted inner, circular layer. The potency for AP II was about 13 times lower in the inner (pD2= 7.48±0.73,n= 6) than in the outer layer (pD2= 8.60 ±0.34,n =6). No significant difference was apparent between the intrinsic activities for AP II in the two layers. The potencies for AP II were for both layers higher than those for VIP while the intrinsic activities for AP II were significantly lower than for VIP and for the reference agonist, isoprenaline in both layers. Atriopeptin II was equally efficient in relaxing the K+‐depolarized anda1‐‐contracted longitudinal segments. Neither theβ‐antagonist, propranolol nor the guanylate cyclase inhibitor, methylene blue, modified the potency or the intrinsic activity of AP II. These results suggest that concentrations of circulating atriopeptins above 10 nM may contribute to reduction of vascular tone by the methylene blue insensitive receptors for AP II and III in the portal‐mesenteric vein region.