Testicular maturation in the rabbit: secretion of testosterone, dihydrotestosterone, 5alpha-androstan-3alpha, 17beta-diol and 5alpha-androstan-3beta, 17beta-diol by perfused rabbit testes-epididymides and spermatogenesis.

Abstract

The rabbit testis-epididymis was perfused in vitro to observe pubertal changes in the secretion of testosterone, dihydrotestosterone, 3o-androstanediol, and 3�i-androstanediol. At selected ages between I and 52 weeks, steroid secretion was correlated with testicular gonadotropin binding activity, plasma androgen levels, serum gonadotropin levels, daily sperm production and spermatogenesis. Testosterone was secreted throughout the period of testicular maturation and accounted for 50% or more of the mass of total androgens produced. Dihydrotestosterone, 3a-androstanediol, and 313-androstanediol (5a-reduced steroids) were not detected until 6 weeks of age but were secreted in increasing quantities during the remainder of pubertal development. The combined mass of testosterone and the 3 5o-reduced androgens thatwas secretedaveraged 0.2, 1.5, 7.4 and 7.8 (pg/testis/h) at 4, 6, 10 and 52 weeks, respectively. Increments in plasma androgen titers coincide with the rise in androgen secretion by perfused testes-epididymides. Circulating androgen concentrations were not correlated with serum LH levels but were tightly coupled to circulating FSH titers (r = 0.93). Testicular and seminal vesicle growth and germ cell differentiation were coincident with graded increments in testosterone and So-reduced androgen production. Each of the indices of testicular function indicated sexual maturity was achieved by 1 8 weeks of age. Two important points emerge from the foregoing results.First, testosterone was the chiefandrogen elaborated throughout pre- and postpubertal testiculardevelopment, a findingwhich contrasts with the predominant formation of 5o-reduced androgens in prepubertal mice and rats. Second, the highly significant correlation between FSH release and plasma androgen levels suggests that FSH may mediate testicular responsiveness to LH during sexual maturation in the rabbit.