Influence of Ovariectomy and Regional Fat Distribution on the Membranous Transducing System Controlling Lipolysis in Rat Fat Cells*

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Abstract
The mechanism by which sex steroid hormones modulate the lipolytic process in fat cells is still not completely understood, particularly at the level of the membrane. As estrogens seem to have regional influence on adipose tissue, we have compared the effects of long term ovariectomy (3 weeks) on the membranous transducing system controlling lipolysis in two rat fat deposits, the femoral sc and the parametrial adipose tissue. These experiments demonstrate the following. 1) Compared to parametrial adipocytes, sc adipocytes have a reduced cAMP production and a decreased beta-adrenoceptor number associated with a reduced lipolytic activity. 2) In parametrial adipocytes, ovariectomy induces a decrease in cAMP production and in both the beta-agonist-stimulated response and the catalytic activity of adenylate cyclase in association with a decreased lipolysis. In contrast, these parameters are unaltered by ovariectomy in sc adipocytes. This study, which reveals site-related differences in the sensitivity of the fat cell adenylate cyclase system to ovarian status, suggests that these differences may explain some of the sex-related regional specificities of adipose tissue metabolism and distribution.

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