Alteration of fate of vasoactive autacoids in pulmonary circulation following monocrotaline-induced lung vascular injury in rats.

1. To learn how pulmonary vascular injury alters the ability of the lung to metabolize vasoactive autacoids, lung vascular lesions were produced in rats by a single subcutaneous injection of monocrotaline (90 mg kg-1), and the blood pressure responses to angiotensin I (AI), angiotensin II (AII), bradykinin, prostaglandin E2 (PGE2) and substance P were examined. Vasoactive agents were given intravenously or intra-arterially. 2. On histological examination of the lung at 3 weeks after monocrotaline treatment, degeneration or necrotization of endothelial cells was evident. 3. The conversion of AI to AII was only slightly depressed by monocrotaline treatment. On the other hand, the depressor response to intravenously injected bradykinin was enhanced in monocrotaline-treated rats. When the rats were pretreated with indomethacin the depressor response to intravenous bradykinin was the same for both control and monocrotaline-treated groups which suggests that endogenous prostaglandins are involved in the enhancement of the response to bradykinin. 4. In monocrotaline-treated rats the depressor response to intravenous PGE2 was significantly enhanced depending on the period following the treatment, while that to the intra-arterial injection did not differ from control. 5. The data suggest that monocrotaline-induced lung injury impairs the metabolism of PGE2 during pulmonary circulation but has little effect on the conversion of AI to AII and the degradation of bradykinin in rats.