Influence of estrogenic status on the lipolytic activity of parametrial adipose tissue in vivo: an in situ microdialysis study.

Ovarian hormones have been shown to modulate the metabolism of adipose cells obtained from adipose tissue of different animals. The aim of this study was to better understand the short- and long-term influences of estrogens on the in vivo lipolytic response of rat parametrial fat pads, determined by measurement of extracellular glycerol concentrations using in situ microdialysis. Possible direct effects of estrogens on lipolysis were studied by perfusion of a potent estrogenic analogue such as moxestrol. Moxestrol (10(-6) M) failed to increase glycerol concentrations in estrus, diestrus, or 8-day ovariectomized animals. However, the basal glycerol concentrations and the lipolytic responses stimulated by 10(-6) M isoproterenol were decreased in parametrial fat pads of diestrus, compared with estrus, rats. Greater decreases in basal and stimulated glycerol concentrations were observed in rats that had been ovariectomized for 8, 15, or 30 days. In ovariectomized rats, isoproterenol-induced lipolysis was restored to the levels observed in diestrus animals by a daily injection of 17 beta-estradiol for a period of 7 days. These results implicate estrogens as long-term modulators of in vivo basal and stimulated lipolytic responses of rat parametrial fat pad.