Variable sensitivity of prepubertal male rats to inhibin-like activity of bull seminal plasma and to testosterone propionate.

Abstract

Bull seminal plasma (bSP) contains inhibin-like activity that can suppress the rise of serum concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH) that otherwise occurs 24 h after castration in the male rat. The sensitivity of prepubertal rats to the, activity in bSP extract varied with the time of the year. In intact rats of the same age, bSP extract could always suppress serum FSH levels, but only sometimes did it affect serum LII; LH suppression occurred during times of greater sensitivity on the part of the acutely castrated rats. These variations in the response of 5-week-old rats to bSP extract may arise from seasonal changes that were observed in the sensitivity of acutely castrated rats to testosterone propionate. The concomitant changes in serum concentrations of LH and testosterone in intact animals indicated that the age of puberty did vary in our colony of rats. Despite the marked changes in the sensitivity of acutely castrated rats to bSP extract and testosterone propionate, serum concentrations of FSH and LH in intact rats showed little change throughout the year.