Control of Rat Preadipocyte Adipose Conversion by Ovarian Status: Regional Specificity and Possible Involvement of the Mitogen-Activated Protein Kinase-Dependent and c-fos Signaling Pathways

As ovariectomy induces obesity in rats, we have investigated the influence of ovariectomy and hormone replacement on the proliferation and differentiation capacities of rat cultured preadipocytes removed from different fat depots (femoral sc, parametrial, and perirenal).Ovariectomy induced increased proliferation and differentiation as well as high mitogen-activated protein (MAP) kinase activity and c-fos protein induction in both confluent and differentiated preadipocytes from perirenal fat depots.In parametrial preadipocytes, ovariectomy also increased proliferation and c-fos protein induction, but failed to alter the capacities of these cells to differentiate.Treatment of ovariectomized rats with estradiol and progesterone reversed the promoting effect of ovariectomy on proliferation, differ-entiation, and c-fos induction in perirenal preadipocytes, but not the MAP kinase activation observed during the proliferative phase.This treatment also reversed the promoting effect of ovariectomy on proliferation and c-fos induction seen in confluent parametrial preadipocytes.In contrast, sc preadipocytes were totally insensitive to ovarian status in terms of proliferation and differentiation capacities, MAP kinase activity, and c-fos induction.This study demonstrates that adipogenesis is site-specifically controlled by the ovarian status in the rat.It also suggests that ovariectomy-induced obesity (mainly abdominal) could be related to changes in some of the signaling pathways controlling adipogenesis in intraabdominal preadipocytes.