title: Maintenance of advanced spermatogenic cells in the adult rat testis: quantitative relationship to testosterone concentration within the testis.
abstract: The studies described herein were designed to examine whether there is a threshold concentration of testosterone (T) within the seminiferous tubules that is required to maintain spermatogenesis in the rat, or alternatively, whether there is a dose-response relationship between the intratesticular T concentration and the maintenance of spermatogenesis. T was administered to intact adult male rats via sustained release polydimethylsiloxane capsules in order to experimentally clamp T at well defined concentrations within the seminiferous tubules. Implantation of T-filled capsules of increasing sizes resulted in linear increases in T concentrations in serum, interstitial fluid, and seminiferous tubule fluid (STF). We examined the effect of step decreases in intratesticular T concentration on the numbers of advanced spermatogenic cells maintained by the testis over a 2-month period. Quantitatively complete spermatogenesis was maintained despite an 80% reduction in the STF T concentration (to approximately 13 ng/ml) from control values. The ability of the testis to maintain complete spermatogenesis was extremely sensitive to further decreases in STF T concentration. Thus, reduction of the STF T concentration from approximately 13 to 9 ng/ml resulted in a reduction in the number of advanced spermatids that were maintained in the testis by approximately 100 x 10(6). Reduction of the STF T concentration to approximately 4 ng/ml resulted in a further reduction in the number of advanced spermatids per testis by 100 x 10(6). Taken together, these data support the contention that there is far more T present within the seminiferous tubules of intact rat testes than is required to maintain quantitatively normal spermatogenesis and reveal for the first time that there is a dose-response relationship between the STF T concentration and the quantitative maintenance of advanced spermatogenic cells in the rat testis.
authors.affiliation: Department of Population Dynamics, Johns Hopkins University School of Hygiene and Public Health, Baltimore, Maryland 21205.
authors.forename: B R
authors.initials: BR
authors.lastname: Zirkin
authors.forename: R
authors.initials: R
authors.lastname: Santulli
authors.forename: C A
authors.initials: CA
authors.lastname: Awoniyi
authors.forename: L L
authors.initials: LL
authors.lastname: Ewing
mesh_terms: D000818:Animals; D004343:Drug Implants; D005640:Follicle Stimulating Hormone / Q000097:blood; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D013087:Spermatids / Q000187:drug effects / Q000502:physiology; D013091:Spermatogenesis / Q000187:drug effects*; D013737:Testis / Q000187:drug effects / Q000502:physiology*; D013739:Testosterone / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D004343:Drug Implants; D013739:Testosterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone