Adrenocortical metabolism of angiotensin in sheep with adrenal transplants

Conscious trained sheep with adrenal gland autotransplants in cervical skin loops were used to study adrenocortical metabolism and clearance of angiotensin (AII) administered by constant systemic infusion. For comparative purposes similar experiments were undertaken in five control sheep with skin loops but no cervical adrenal tissue. During AII infusions (0.33 microgram/min for 30 min), loop venous-arterial AII ratios (0.42--0.62 were similar in both groups of sheep. Measured AII clearances across the skin loop in sheep with and without adrenal transplants were 400--600 and 100--150 pg/min, respectively, which correlated with blood flow (r = 0.79), but showed no relation to aldosterone secretion rate. Analysis of AII immunoreactive fragments showed similar proportions of octa-, hepta-, and hexapeptide fractions (64, 26, and 5%, respectively) in adrenal arterial, adrenal venous, and systemic venous plasma. These studies do not support selective heptapeptide uptake or metabolism by adrenal tissue in vivo and indicate that specific adrenal binding of AII is likely to be less than 400 pg/min at arterial AII concentrations approximating 120 pg/ml.