Suppression of Spermatogenesis by Testosterone in Adult Male Rats: Effect on Fertility, Pregnancy Outcome and Progeny 1

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Abstract
The relationship between decreasing spermatogenic activity and fertility, pregnancy outcome and the progeny is poorly understood. To study this relationship a model where testosterone is given by a sustained release device is used. Adult male Sprague-Dawley rats received empty or testosterone-filled implants measuring 0.5, 1.0, 2.0, 3.0, 4.0 and 8.0 cm. On Day 90 and again on Day 104 each male was exposed to 2 females in proestrus. Twenty days later the females were killed. Corpora lutea, implantation sites, resorptions and live normal and abnormal fetuses were counted. Sperm counts in the caput-corpus region of the epididymis in the 3.0-, 4.0- and 8.0-cm testosterone treatment groups were 12.6, 3.0 and 29.9% of control, while those in the caudal region were 19.8, 4.0 and 50.8% of control, respectively. The number of females with spermatozoa in the vagina after breeding was significantly diminished only in the animals treated with the 4.0-cm testosterone implants (control, 95.8%; 4.0-cm, 50%) while the number of pregnant females per sperm-positive females was markedly reduced in the females mated with both the 3.0-cm and 4.0-cm testosterone implants (control, 82.6%; 3.0-cm, 10.0%; 4.0-cm, 7.7%). There was no effect on the numbers of corpora lutea, on the incidence of pre- or post-implantation loss, malformations, or on the numbers of pups/litter. Individual animals with a decrease in caudal epididymal spermatozoal reserves to < 5 million, however, are infertile. A decrease in epididymal spermatozoal reserves mediated by testosterone does not cause an increase in teratogenicity in the resultant progeny. [Implications for male contraceptive development and role of azoospermia are considered.].

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