Effects of oral estrone on rat energy balance.

Oral doses of estrone from 10 nmol/(kg day) to 10 micromol/(kg day) were given to adult Wistar male rats for 10 days. Body composition, energy balance, total body estrone balance and plasma metabolites and hormones were measured at the end of the treatment. Body weight (as well as food intake, body energy, fat and water accrual) increased at doses in the 10--100 nmol/(kg day) range, but decreased at higher doses. Energy expenditure decreased with increasing doses of estrone. Plasma metabolite changes suggested the maintenance of energy homeostasis, and lipid parameters indicated that lipid mobilization increased with the increasing doses of estrone. Plasma estrone, acyl-estrone and estradiol levels decreased at low doses and increased at high doses of estrone. We conclude that: (a) repeated estrone gavages, even at very high doses, do not result in the accrual of estrone in the body; (b) low doses of estrone promote growth and high doses decrease body mass and fat accretion; (c) administration of estrone at low doses decreases its circulating levels and the levels of estradiol and acyl-estrone, a situation reverted at higher doses and (d) estrone administration induces a dose-dependent shift towards lower energy expenditure.