Changes in serum testosterone levels following acute LH treatment in immature and mature rats.

Abstract

The concentration of testosterone in spermatic vein and peripheral blood increases in the rat with the approach of sexual maturity. The hypothesis that increased testosterone levels are due to the sensitivity of the testes to LH increasing during puberty was examined by measuring serum testosterone levels in immature and adult rats after acute stimulation with bovine LH. Serum testosterone levels were found to be significantly higher in male rats aged 83 days compared to rats aged 37 days whereas serum LH levels in the same groups were the same. Serum testosterone levels in 90-day-old male rats were elevated by 30 minutes after ip administration of 10 mcg LH/100 gm body weight and remained elevated through 150 minutes. In a similar experinent with 31-day-old males testosterone levels were elevated at 90 minutes but not at 30 or 180 minutes; with 37-day-old rats testosterone levels were elevated by 60 minutes and remained elevated through 150 minutes. 100 minutes after receiving 1 mcg LH/100 gm body weight testosterone levels in 36-day-old rats were slightly elevated; 10 mcg raised their testosterone levels to the normal adult male range but 100 mcg caused no further increase. 76-day-old males did not respond to 1 mcg LH/100 gm body weight (31.7 ng/ml) was significantly higher than the level attained by the immature rats (5.85 ng/ml) in response to the same LH dose. The significantly higher serum testosterone levels found in the adult rats receiving 10 mcg LH/100 gm body weight indicate that changes in the responsiveness of the testis to LH may be an important part of puberty in the male rat.(AUTHORS MODIFIED)