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

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.

Characteristics of the α2/β‐adrenoceptor‐coupled adenylate cyclase system and their relationship with adrenergic responsiveness in hamster fat cells from different anatomical sites

“…The same picture seems also to apply to the rat, since, as recently reported by us, subcutaneous adipocytes from female rats have a reduced lipolytic response to catecholamines compared to parametrial adipocytes [6]. In most of these studies, the differences observed in catecholamine-stimulated lipolysis between the various adipose sites have been mainly attributed to differences in their number of adrenoceptors ; human adipocytes having been shown to possess lower numbers of P-adrenoceptors and higher numbers of a,-adrenoceptors in the subcutaneous region than in the intra-abdominal region [5].…”

Estradiol-Induced Inhibition of Body Weight Gain and Reduction of Food Intake Are Not Associated with Diurnal Rhythmicity.

“…6. This effect of estradiol on the BW is considered to be ascribed, at least in part, to the suppression of body fat accumulation [9][10][11][12][13][14]. The results of the present study clearly show that these inhibitory effects of estradiol on the FI and the BW gain are exerted throughout the day without any appreciable difference in the extent of suppression between the light and dark phases.…”

Estradiol does not directly regulate adipose lipolysis

“…8 In vitro, visceral adipocytes from OVX rodents have shown reduced catecholamine responsiveness. 9 In vivo E2 treatment of 4-30 d augmented in vitro adipocyte lipolytic response to various b 2 agonists in OVX E2 rats vs. OVX. 11,[29][30][31] Each of these studies examined adipocytes isolated by collagenase, devoid of additional cell types and typical crosstalk in adipose tissue.…”

“…14 In rats, the evidence is equivocal; in one study, adipocytes isolated from femoral subcutaneous adipose in OVX rats were not different from SHAM controls in their response to isoproterenol. 9 In another study, OVX rats showed a 50% reduction in b 2 -stimulated glycerol release from subcutaneous adipose tissue, as measured by microdialysis, which was restored after 7 d of E2 treatment. 15 Although these studies provide some insight into the effects of E2 loss on adipose tissue metabolism, the majority fail to control for hyperphagia by pair-feeding, thereby making it difficult to conclude whether the chronic effects of E2 on lipolysis are directly due to E2 per se, or rather due to secondary effects subsequent to reductions in energy intake 16 or changes in fat cell size.…”

“…Reduced adenylate cyclase activity and cAMP production have been observed in visceral adipose tissue from OVX animals. 9 In OVX mice, there is a reduced translocation of adipose triglyceride lipase (ATGL) to the lipid droplet and blunted Ser660 phosphorylation of hormone sensitive lipase (HSL) in response to acute exercise. 10 In visceral adipocytes isolated from OVX animals, basal and catecholamine-stimulated lipolysis are lower compared with controls, which is restored after 4-30 d of E2 replacement.…”