Sex differences in body weight and eating: Organization and activation by gonadal hormones in the rat

Abstract

Female rats injected on the fifth day of life with testosterone propionate (TP) or estradiol benzoate (EB) weigh more in adulthood than control animals injected with oil. If rats are ovariectomized prior to steroid treatment on Day 5, body weight differences in adulthood are reduced and their initial appearance during development is delayed. Neonatal TP or EB treatment increases responsiveness to the weight-promoting effects of androgens in adulthood and decreases adult responsiveness to the weight depressing actions of ovarian hormones. We propose that hormonal stimulation in infancy affects body weight by altering hormonal sensitivity of neural weight regulating mechanisms. Non-neural mechanisms and behavioral effects which might contribute to changes in body weight are also considered. The adult sex difference in body weight is multiply determined by postnatal organizational and activational effects of gonadal hormones as well as by non-hormonal genetic factors and/or prenatal testicular secretions. The sex difference in eating is less subject to early organizing actions of hormones and is primarily attributable to the different hormones secreted by male and female gonads beginning sometime after the end of the neonatal organizational period.