Characterization of α-Adrenoceptor Activity in Term-newborn Piglet Mesentery

Abstract

Abstract For further characterization of neonatal mesenteric α1-adrenoceptor populations, an extracorporeal perfusion circuit was established to control intestinal blood flow in 0-2 day old piglets. Activation of α1-adrenoceptors was first documented by observing dose-dependent increases in mesenteric perfusion pressure after intra-mesenteric arterial injection of methoxamine and noradrenaline. Peripheral intravenous injections of WB 4101 (a competitive α1A-adrenoceptor antagonist), but not clorethylclonidine (CEC, an α1B-adrenoceptor antagonist), significantly (P < 0.05, analysis of variance) blunted mesenteric vasoconstrictor responses to those agonists. That the mesenteric vasoconstrictor response to mesenteric plexus stimulation was unaltered by CEC, but was muted by both WB 4101 and SK&F 104856 (a post-junctional α1- and α2-adrenoceptor antagonist) suggests that pre- and post-junctional α1A-adrenoceptors are present and functional at birth.