Role of sympathetic nerves in effects of estradiol on rat white adipose tissue.

Two experiments examined the role of the sympathetic nerves in estradiol-induced fat pad weight losses in ovariectomized (OVX) rats. Rats were OVX, and the retroperitoneal white adipose tissue (RWAT) was unilaterally denervated 4 wk later. After 14 days of treatment with estradiol benzoate (EB, 2 micrograms/day), the intact pads lost 23% more weight than the denervated pads. There was no effect of denervation on fat pad weight or on cytosol estrogen receptor concentration in RWAT in the animals treated with sesame oil vehicle. These data suggest that the sympathetic nerves play a role in estrogen-induced reductions in fat pad weight but not via changes in adipose tissue cytosol estrogen receptors. A second experiment examined whether estradiol-induced fat pad weight losses are accompanied by increased norepinephrine (NE) turnover, an index of sympathetic activity, in adipose tissue. Rats were OVX and treated with EB or sesame oil vehicle. NE turnover was assessed by measuring the decline of tissue NE over time after injection of alpha-methyl-p-tyrosine, an inhibitor of tyrosine hydroxylase activity and thus NE biosynthesis. NE turnover in RWAT, but not heart, was significantly greater in animals treated with EB, suggesting that estradiol decreases fat pad weight in part by increasing sympathetic nervous system activity. It is possible that estradiol acts in the brain to regulate the activity of the sympathetic nerves to white adipose tissue and peripherally to alter adipose tissue responsiveness to catecholamines.