CHARACTERIZATION OF ALPHA-ADRENOCEPTOR ACTIVITY IN THE PRETERM PIGLETMESENTERY

To characterize neonatal mesenteric alpha-adrenoceptor populations, an extracorporeal perfusion circuit was established to control intestina l blood flow in prematurely delivered (by cesarean section at 90% of g estational age) piglets. Activation of alpha(1)-adrenoceptors was docu mented by observing dose-dependent increases in mesenteric perfusion p ressure after intramesenteric arterial injection of methoxamine; alpha (2)-adrenoceptor activity was confirmed by finding similar increases i n mesenteric perfusion pressure after intramesenteric arterial injecti ons of BHT 933. Peripheral intravenous injections of WB 4101 (a compet itive alpha(1A)-adrenoceptor antagonist), but not clorethylclonidine ( CEC, an alpha(1B)-adrenoceptor antagonist), significantly blunted (P < .05, ANOVA) the mesenteric vasoconstrictor responses to methoxamine. The mesenteric vasoconstrictor response to BHT 933 (an alpha(2)-adreno ceptor agonist) also was blunted by WB 4101, but not by CEC. These dat a suggest that alpha(1A) - and alpha(2)-adrenoceptors can be activated in the small intestinal mesentery of piglets well before they reach f ull-term maturation, although receptor specificity has not been fully established. Copyright (C) 1996 by W.B. Saunders Company.