Effects of gonadectomy and chlorpromazine treatment on prolactin, LH, and FSH secretion in young and old rats of both sexes

Old male rats, and female rats in the states of senile persistent estrus (PE) and senile repetitive pseudopregnancy (RPD) were compared with young controls in the change of serum prolactin (PRL), LH, and FSH concentrations after gonadectomy and chlorpromazine (CPZ) treatment. Old male rats (18–21-month old) and PE (12–15-month old and 18–19-month old) and RPD (18–23-month old) female rats showed higher serum PRL levels. In both young and old male rats, orchidectomy did not cause any significant changes in serum PRL levels. The effect of ovariectomy on serum PRL levels was smaller in old female rats. CPZ treatment increased serum PRL levels in young controls of both sexes, 12-month old males and 12–15-month old PE rats. The sexual difference in PRL secretion in response to CPZ was observed at these ages. In 18–21-month old males and 18–23-month old females, CPZ did not significantly increase serum PRL levels. These results suggest that the higher serum PRL levels in intact old male and female rats may be partly due to the lowered activity of the hypothalamic dopaminergic inhibition. The changes in serum LH levels in response to ovariectomy were smaller in old female rats than in young controls, whereas male rats did not show any age-related changes in response to orchidectomy on serum LH levels. There was no appreciable age-difference in the increase in serum FSH levels after gonadectomy in either sex.