Effect of unilateral and bilateral castration and cryptorchidism on serum gonadotrophins in the rat.

The effects of unilateral and bilateral cryptorchidism and castration on serum concentrations of testosterone, FSH and LH in adult male rats were examined. The results provide no evidence for compensatory growth or development of the remaining scrotal testes up to 32 days after unilateral castration, although the scrotal testis of unilaterally cryptorchid rats showed enlargement when compared with those of control rats (P less than 0 - 05) at 32 days. Unilateral treatments had few significant effects on serum hormones, but testosterone was increased on day 4 (P less than 0 - 05) in unilaterally cryptorchid rats and on day 32 (P less than 0 - 05) in unilaterally castrated rats, compared with controls, and FSH levels were higher in unilaterally castrated rats on day 16 (P less than 0 - 05). Bilateral cryptorchidism caused an increase in serum FSH within 4 days (P less than 0 - 05) and in serum LH by 8 days (P less than 0-05) after surgery, with both hormones reaching levels double those found in control rats (P less than 0 - 01) by day 16, while testosterone levels were maintained at or above control values. Bilateral castration resulted in a marked decrease in testosterone levels (P less than 0 - 01) and a sharp increase in serum gonadotrophins. FSH had nearly doubled (P less than 0 - 01) and LH had increased fourfold (P less than 0 - 01) 4 days after castration, their levels reaching 773% (LH) and 287% (FSH) of control values by 32 days (P less than 0 - 01). The observations support the hypothesis of a separate, testosterone-independent feedback system of the testis on the hypophysis.