DIFFERENTIAL PATTERNS OF RELAXATION BY SYNTHETIC ATRIAL PEPTIDE (APII) IN THE PULMONARY-ARTERY, ASCENDING AND DISTAL ABDOMINAL-AORTA

The vasodilatory effects of the synthetic rat atriopeptin (APII) have been studied in vitro in agonist-contracted, endothelium-denuded segments of the rat pulmonary artery, the ascending, and the distal abdominal aorta. In the pulmonary artery the contractures to methoxamine were inhibited more potently by APII (pD2 = 9.10 ± 0.40, n = 6) than by the vasodilatory neuropeptide VIP (pD2 = 7.37 ± 0.66, n = 6). The intrinsic activity of APII was 0.46 ± 0.16 (n = 6). In segments previously exposed to either VIP or the β2-agonist salbutamol, APII was a near complete agonist (α = 0.82 ± 0.17, n = 7 and 0.84 ± 0.14, n = 6, respectively) without significant changes in the potencies. APII was a complete agonist also for the inhibition of the α-agonist-contracted segments of the aorta, however, with potencies 10-fold lower than in the pulmonary artery. VIP was without functionally significant effects in the aorta. The tachykinins (CGRP, SP, Neurokinins A and B) were without effects in all segments tested. In the ascending aorta, APII induced a long-lasting tachyphylaxis to the α-agonists, nearly completely abolishing the subsequent responsiveness to NA and methoxamine for more than 4 h. © 1990.