Effect of estradiol benzoate on the pituitary-gonadal axis in the intact male rat.

Adult male rats were treated with 50 microgram of estradiol benzoate daily for 28 days. The sex organs and pituitary weights showed changes classically associated with estrogen treatment. Both plasma and testicular testosterone levels diminished to almost trace level 24 hours after the first estrogen injection and remained at that level throughout the experimental period. The pituitary LH levels and concentration showed a progressive decline; however, the plasma LH levels remained unchanged throught the experimental period. These findings suggest that in intact adult males, estrogen affects testicular testosterone production directly. These observation suggests the necessity for reevaluation of the current concepts concerned with testis-pituitary feedback mechanisms.