ADRENOMEDULLIN IS INACTIVATED IN THE LUNGS OF NEONATAL PIGLETS

Adrenomedullin, a novel 52 amino acid peptide normally present in adul t human plasma, has been shown to induce systemic hypotension in the a dult rat, pig and cat, and in the new-born piglet. Little is known abo ut the site(s) of adrenomedullin inactivation in adults or neonates. G roups of five 0-2 day old and 2-week old anaesthetized piglets were pr epared to enable continuous monitoring of cardiac output, mean systemi c arterial pressure, mean pulmonary artery pressure, mean systemic vas cular resistance and mean pulmonary vascular resistance. In both age g roups, injections of human adrenomedullin(1-52) into the left atrium p roduced significant (P < 0.05) reductions in mean systemic arterial pr essure and mean pulmonary artery pressure. Although injections of simi lar doses of human adrenomedullin(1-52) into the right atrium produced significant (P < 0.05) decreases in mean pulmonary artery pressure, t here were no appreciable alterations in mean systemic arterial pressur e in either age group. These results suggest that the systemic vasodil ator properties of human adrenomedullin(1-52) are reduced upon first p ass through the pulmonary circulation in 2-week old piglets, a phenome non that is present at birth.