Neonatal androgenization and estrogenization and the hormonal induction of sexual receptivity in rats

Abstract

Administration of male sex hormone to neonatal female rats has been shown to inhibit the development of the capacity of the female to respond to female sex hormones in adulthood with the display of sexual receptivity (lordosis). Since the hormonal induction of sexual receptivity in the ovariectomized female typically involves the administration of both estrogen and progesterone, the failure of virilized females to show lordosis following treatment with these two hormones could be due to a diminished sensitivity to estrogen, a diminished sensitivity to progesterone, or both. One purpose of the present study was to determine which of these alternatives obtains. A second purpose of the study was to compare neonatally estrogenized females with neonatally androgenized females, in an attempt to determine to what extent neonatal estrogenization exactly mimics neonatal androgenization. Female rats were given either an injection of testosterone propionate, estradiol benzoate, or oil on the day of birth. Male rats were given a control injection of oil on the day of birth. As adults all rats were gonadectomized and tested for sexual receptivity following either estrogen administration or administration of both estrogen and progesterone. Females given oil at birth showed moderate levels of sexual receptivity when administered estrogen alone. Levels increased as estrogen dose was increased. At each dose level, females given oil at birth and estrogen and progesterone in adulthood showed higher levels of receptivity than did females given only estrogen. Male rats, androgenized females, and estrogenized females failed to show significant receptivity at any dose level of estrogen stimulation, regardless of whether or not progesterone was also administered. It was concluded that a major effect of neonatal androgen stimulation, exogenous or endogenous, is an inhibition of the development of estrogen sensitive systems for lordotic behavior. In this regard, neonatal estrogenization appears to mimic the effects of neonatal androgenization.