Serum gonadotrophins and follicular development in immature rats after early androgen administration

Follicular development and serum gonadotrophin levels were studied in female rats after neonatal androgen administration. After injection of 1250 mug testosterone propionate (TP) on day 5 after birth the composition of the follicular population was altered: at nearly all ages the number of pre-antral follicles (follicular volume 2-20 X 10(5) mum2) was lower than in oil-treated rats, in some cases the number of small antral follicles (21-249 X 10(5) mum3) was also lower. Furthermore levels of serum follicle-stimulating hormone and luteinizing hormone were decreased from day 7 to day 20 suggesting that the high gonadotrophin levels before day 20 are of importance for normal follicular development. In contrast, final follicular maturation in TP-treated rats was enhanced; at day 35 more large antral follicles (follicular volume greater than or equal to 500 X 10(5) mum3) were present in TP-treated rats than in oil-treated rats. The presence of more large antral follicles was accompanied by higher plasma oestradiol concentrations, higher uterine weights and advanced vaginal opening. These results demonstrate an inhibition of normal follicular growth and an acceleration of ovarian maturation after neonatal androgen administration.