EFFECT OF PREPUBERTAL HEMIORCHIDECTOMY ON THE RESPONSE OF THE TESTIS TO LUTEINIZING-HORMONE

Administration of FSH to hypophysectomized male rats has been shown to increase the capacity of the testes to secrete testosterone in response to LH. Studies were done to assess the effect of increased endogenous FSH on the response of the testis to LH. At 17 and 24 days of age, animals hemiorchidectomized at 10 days of age had significantly higher serum FSH levels and testicular weights than sham-operated rats. To study the testicular response to LH in vivo, hemiorchidectomized animals were sham-operated and the sham-operated animals were hemiorchidectomized at 17 or 24 days of age. Luteinizing hormone (30 μg/100 g body wt) or saline was administered immediately after the operation and the animals were autopsied 90 min later. Chronic hemiorchidectomy significantly increased the serum testosterone response to LH at 17 but not at 24 days of age. The testicular response to LH in vitro was also investigated. Testes from rats hemiorchidectomized or sham-operated at 10 days of age and killed at 17 and 24 days of age were incubated for 3 hr in the presence or absence of 100 ng LH/ml incubation medium. Significantly more 5α-androstane-3α, 17β-diol and androsterone were produced by the testes from hemiorchidectomized than from sham-operated animals at 17 days of age but not at 24 days of age. The production of testosterone in vitro was not influenced by hemiorchidectomy at either age. These results suggest that serum FSH concentration is the factor limiting LH responsiveness before but not after the prepubertal increase in FSH levels. However, treatment of intact rats from 10 to 16 days of age with 20 μg rat FSH/day did not increase the serum testosterone response to LH.