Search

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.

To detect the presence in adipose tissue of peptides known to affect tissue growth and to investigate potential regional differences, epididymal and perirenal adipose tissue depots from male Sprague-Dawley rats were separated into adipocyte and stroma-vascular fractions by collagenase digestion, sequential centrifugation and filtration. Identity and integrity of the fractions were demonstrated by light and electron microscopy, while dose-response curves for angiotensin-converting enzyme (ACE) were performed, revealing maintained functional capacity of the stroma-vascular fraction. ACE, atrial natriuretic peptide (ANP), and transforming growth factor-alpha (TGF-alpha) concentrations were significantly greater in epididymal than perirenal stroma-vascular tissue. Adipocyte fractions from both depots contained significant concentrations of ANP and TGF-alpha. There was no detectable ACE in the adipocyte fractions, indicating that no contaminating stromal-vascular cells were present in these fractions. These data show significant concentrations of peptides with effects on growth in subfractions of adipose tissue and demonstrate regional differences in concentrations between fat depots.