Regulation of adenylate cyclase in plasma membranes of human intraabdominal and abdominal subcutaneous adipocytes.

Fat cells were isolated from human subcutaneous, omental, and mesenteric adipose tissue. Omental fat cells were the smallest (438 pL), subcutaneous cells were intermediate (494 pL), and mesenteric cells were the largest (600 pL). There was no difference in the stimulation of adenylate cyclase by isoproterenol in plasma membranes of adipocytes prepared from the three sites. N6-(phenylisopropyl)adenosine inhibited 7-deacetyl-6-(N-acetylglycyl)forskolin-stimulated adenylate cyclase activity more potently in subcutaneous than in intraabdominal (especially omental) fat cell membranes. Kd values of the adenosine A1 receptors for 1,3-[3H]dipropyl-8-cyclopentylxanthine were similar in the three fat depots, but the receptor number as calculated per milligram protein was lower in omental than in abdominal subcutaneous adipocytes. Differences in adipocyte size cannot explain regional differences in the regulation of adenylate cyclase.