Effect of treatment with GnRH antagonist, GnRH antiserum and bromocriptine on pituitary-testicular function of adult rats.

Gonadotropin secretion of adult male rats was inhibited by one-week treatment with a GnRH antagonist analogue (N-acetyl-Ala1,D-p-Cl-Phe2,D-Trp3,6-GnRH, Ant.) or a GnRH antiserum (A/S). Since Ant. but not A/S binds to GnRH receptors (R), it was expected that comparison of the two treatment regimes would elucidate a physiological role for testicular GnRH-R. Furthermore, the effect of combined gonadotropin and prolactin deficiency was studied in rats treated with Ant. and bromocriptine (BR). Available pituitary GnRH-R were decreased by both Ant. and A/S (P less than 0.01), but not by BR. Testicular content of free GnRH-R was decreased by Ant. by 70-80% (P less than 0.01), probably owing to occupancy, but A/S and BR had no effect on these binding sites. Serum LH and FSH fell by about 75% with Ant. and A/S treatments (P less than 0.01), and Prl by 90% with BR (P less than 0.01). Intratesticular testosterone (T) decreased significantly with Ant. and A/S treatment (P less than 0.01-0.05), but was unaffected by BR. Only Ant. and BR treatments together, but neither alone, were able to suppress Leydig cell capacity to produce T in vitro. Relative blockade of C21 steroid side-chain cleavage by Ant. and A/S was suggested by elevated progesterone (P) and/or P/T ratios in the serum and testis tissues. Ant. and A/S had no effect on testicular LH and FSH-R, but both decreased testicular Prl-R by about 50% (P less than 0.01-0.05).(ABSTRACT TRUNCATED AT 250 WORDS)