Renal and adrenal responses to hypoxemia during angiotensin-converting enzyme inhibition in lambs.

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Abstract
Chronically catheterized lambs (4-37 days postnatal age) (n = 35) were studied to test the hypothesis that the products of angiotensin-converting enzyme activity are involved in renal and adrenal responses to normocapnic hypoxemia in immature lambs. Arterial angiotensin II (from 111.0 .+-. 38.8 to 71.0 .+-. 38.8 pg/ml, P < 0.01) and aldosterone (from 128.0 .+-. 98.0 to 62.1 .+-. 27.9 pg/ml, P < 0.01) concentrations were significantly decreased and vasopressor responses to angiotensin I were greater than 90% inhibited by continuous i.v. infusion of angiotensin-converting enzyme inhibitor (captopril, 2.5 .mu.g/kg per min, n = 16). Baseline mean arterial pressure (64 .+-. 14 vs. 78 .+-. 9 mm Hg) and urinary Na+ excretion rate (UNaV 3.04 .+-. 2.83 vs. 15.00 .+-. 20.00 .mu.eq/min) were significantly (P < 0.05) decreased in captopril-treated lambs vs. control lambs. Baseline arterial plasma renin activity was significantly (P < 0.01) increased in captopril-treated vs. control lambs (8.6 .+-. 9.0 vs. 100.0 .+-. 64.0 ng/ml per h). Normocapnic hypoxemia (PO2 38 .+-. 6 torr for 30 min) during captopril infusion was associated with no significant (P > 0.05) changes in renal hemodynamics and function, including glomerular filtration rate (from 0.34 .+-. 0.24 to 0.35 .+-. 0.25 ml/min per g). Urinary prostaglandin E excretion rate (from 0.655 .+-. 0.703 to 1.310 .+-. 1.020 ng/min) and adrenal blood flow (from 2.67 .+-. 1.69 to 6.24 .+-. 3.73 ml/min per g) increased significantly (P < 0.05) under these conditions. Arterial epinephrine (from 0.11 .+-. 0.07 to 1.1 .+-. 1.8 ng/ml), norepinephrine (0.48 .+-. 0.38 to 3.2 .+-. 5.4 ng/ml), and arginine vasopressin (from 5.11 .+-. 2.20 to 10.70 .+-. 8.61 .mu.U/ml) also increased significantly (P < 0.05) in response to hypoxemia during angiotensin-converting enzyme inhibition with captopril. None of these responses to hypoxemia were significantly different from that of uninhibited (control) lambs (n = 19). Cortisol response to hypoxemia was significantly (P < 0.05) less in captopril-treated lambs (captopril vs. control, -1.00 .+-. 1.90 vs. 3.40 .+-. 3.30 .mu.g/dl). Apparently the products of angiotensin-converting enzyme activity are not important regulators of renal responses to hypoxemia, but may be involved in cortisol responses to normocapnic hypoxemia in immature lambs.