Identification and characterization of angiotensin II receptors in rat epididymal adipocyte membranes.

To better understand the role of the mitogenic vasoactive peptide angiotensin II (AII) in growth and differentiation, we have investigated the existence of membrane receptors for this peptide in rat adipocytes. Following isolation of epididymal fat cells, membrane protein was removed and incubated with varying concentrations of 125I-AII with or without submicromolar concentrations of unlabeled AII. Binding of AII was highly specific, rapid, and reversible. Scatchard analysis indicated that adipocyte membranes contain a high-affinity AII receptor with a Kd of 0.90 nmol/L and a binding site concentration (Bmax) of 53.7 fmol/mg protein. Additional pharmacologic analyses resulted in a rank order potency for peptide agonists and antagonists similar to that reported for the vascular receptor. Determination of subtype specificity with selective organic compounds indicated that the epididymal adipocyte receptor was displaced at low concentrations of DuP753, a selective AT1 subtype antagonist. These studies have successfully identified and characterized a high-affinity membrane receptor for AII in fat cells, further establishing adipose tissue as a peripheral site containing regulatory components of the local renin-angiotensin system.