Biology of Reproduction, Vol 18, 212-218, Copyright © 1978 by Society for the Study of Reproduction

Testicular Maturation in the Rabbit: Secretion of Testosterone, Dihydrotestosterone, 5-Androstan-3,17-diol and 5-Androstan-3, 17-diol by Perfused Rabbit Testes-Epididymides and Spermatogenesis

¹ Division of Reproductive Biology, Department of Population Dynamics, School of Hygiene and Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205 and Institute of Reproductive Biology, Department of Zoology, University of Texas-Austin, Austin, Texas 78712

The rabbit testis-epididymis was perfused in vitro to observe pubertal changes in the secretion of testosterone, dihydrotestosterone, 3-androstanediol, and 3-androstanediol. At selected ages between 1 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, 3-androstanediol, and 3-androstanediol (5-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 5-reduced androgens that was secreted averaged 0.2, 1.5, 7.4 and 7.8 (µg/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 5-reduced androgen production. Each of the indices of testicular function indicated sexual maturity was achieved by 18 weeks of age. Two important points emerge from the foregoing results. First, testosterone was the chief androgen elaborated throughout pre- and postpubertal testicular development, a finding which contrasts with the predominant formation of 5-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.

Note:
ACKNOWLEDGMENTS The authors express their appreciation to Donald W. Carroll and Elizabeth Higginbottom for expert assistance. Reagents used to assay plasma FSH were provided through the courtesy of Dr. Jimmy Neill, Department of Physiology, Emory University, Atlanta, Georgia. The antibody used to assay plasma androgen was kindly provided by Dr. H. Hafs, Michigan State University.

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