ANGIOTENSIN-II-1 RECEPTOR-MEDIATED CONTRACTION OF PULMONARY-ARTERY AND ITS MODULATION BY PROLYLCARBOXYPEPTIDASE

To determine the subtype of angiotensin II (ANG II) receptor involved in the contraction of pulmonary artery and to elucidate its possible modulation by endogenous peptidases, we studied canine isolated pulmonary arterial rings under isometric conditions in vitro. Addition of ANG II caused a concentration-dependent contraction, an effect that was not altered by the ANG II 2 receptor antagonist EXP655 but was depressed by the ANG II 1 receptor antagonist DuP 753 so that the ANG II response curves were displaced to higher concentration by 1.5-2.0 log U (P < 0.001). Pretreatment of tissues with the prolylcarboxypeptidase (PCP) inhibitor p-methylphenyl sulfonylfluoride potentiated the ANG II-induced contraction, with the concentration required to produce a half-maximal effect of ANG II being decreased from 4.1 +/- 0.9 X 10(-9) to 3.8 +/- 0.5 X 10(-10) M (P < 0.001), whereas other peptidase inhibitors such as p-chloromercuriphenyl sulfonic acid, amastatin, and phosphoramidon had no effect. The p-methylphenyl sulfonylfluoride-induced potentiation was abolished by the removal of endothelium, but it was still observed in the presence of N-G-nitro-L-arginine methyl ester in the endothelium-intact tissues. The PCP activity in the tissues was reduced by the removal of endothelium from 645 +/- 88 to 91 +/- 29 nmol.mg protein(-1) h(-1) (P < 0.001), and cultured endothelium had the activity of 404 +/- 39 nmol.mg protein(-1) h(-1). These results suggest that ANG II contracts pulmonary artery via ANG II 1 receptor and that PCP localized to the endothelium may have a modulatory role in the ANG II-induced pulmonary vasoconstriction.