PULMONARY VASODILATION TO ADRENOMEDULLIN - A NOVEL PEPTIDE IN HUMANS

The present study investigates the effects of human adrenomedullin (AD M) on the pulmonary vascular bed of isolated, blood-perfused rat lung. Because pulmonary blood flow and left atrial pressure were constant, changes in pulmonary arterial pressure directly reflect changes in pul monary vascular resistance. Under conditions of resting (low) pulmonar y vasomotor tone, intra-arterial bolus injections of ADM(1-52) and two truncated sequences of ADM-(1-52) [ADM(1-12) and ADM-(13-52)] did not alter pulmonary arterial pressure. When pulmonary vasomotor tone was increased by U-46619, a thromboxane A(2) mimic, intra-arterial bolus i njections of ADM-(1-52) and ADM-(13-52) at similar doses produced simi lar, dose-dependent reductions in pulmonary arterial pressure. On a mo lar basis, ADM-(1-52) had greater pulmonary vasodilator activity than isoproterenol. In contrast, ADM-(1-12) had no activity. When pulmonary vasomotor tone was actively increased to the same level using KCl, th e pulmonary vasodilator activity of ADM-(13-52) was decreased 10-fold. The present data demonstrate that ADM-(1-52) dilates the pulmonary va scular bed and suggest that the pulmonary vasodilator activity of ADM is greater on pulmonary blood vessels preconstricted through a recepto r-dependent mechanism. Because meclofenamate, nitro-L-arginine methyl ester, methysergide, BW A-1433U83, U-37883A, and calcitonin gene-relat ed peptide [CGRP-(8-37)], a CGRP-receptor antagonist, did not alter th e pulmonary vasodilator response to ADM-(1-52), the present data sugge st that ADM dilates the pulmonary vascular bed independently of cycloo xygenase products, endothelium-derived relaxation factor, serotoninerg ic receptors, adenosine(1) purinoreceptors, ATP-dependent potassium ch annels, and CGRP receptors. Furthermore, only a fragment of the ADM mo lecule is necessary to dilate the pulmonary vascular bed. The present data suggest that ADM may represent a novel regulatory peptide in the lung.