Endocrinological study of testicular descent in the rabbit

The process of testicular descent was investigated in the rabbit. In the rabbit, the testis descends on or about the sixth postnatal day and by 22 days of age, the testes are almost always (27 of 28 testes) found in the scrotum. The administration of 17β-estradiol (E₂) daily from Day 1 to Day 21 of age completely inhibits testicular descent ($\text{0}\text{26}$) at Day 22 of age. This inhibition of testicular descent by E₂ at Day 22 of age is completely reversible by the simultaneous treatment with 3α-androstanediol (3α-Diol) ($\text{12}\text{12}$) and only partially reversible by the simultaneous treatment with dihydrotestosterone (DHT) ($\text{12}\text{20}$) or human chorionic gonadotropin (hCG) ($\text{9}\text{18}$). Testosterone does not reverse the inhibition of testicular descent produced by E₂ ($\text{1}\text{20}$). The plasma testosterone level at Day 22 of age (600 ± 274, pg/ml ± SEM) was suppressed in the E₂-treated group (<100 pg/ml) and elevated in the group exposed to E₂ plus hCG (2367 ± 1224 pg/ml). From these data, it was concluded that in the rabbit (a) testicular descent appears to be an androgen-mediated event, (b) the active androgen involved in this event is most likely 3α-Diol or DHT, and (c) testicular descent appears to be under the regulation of the hypothalamic-pituitary-testicular axis.