Dose-dependent effects of perinatal hypothyroidism on postnatal testicular development in rat offspring.

The role of thyroid hormones in gonad development remains incompletely understood. We examined the dose-related effects of perinatal hypothyroidism induced by a reversible goitrogen, 6-propyl-2-thiouracil (PTU), on reproductive development in male rat offspring. Timed-pregnant Sprague-Dawley rats were orally administered PTU (0, 0.5, 1.0, or 2.0 mg/kg/day) by gavage from gestational day 15 through postnatal day 20. We observed a significant dose-dependent decrease in body weight in offspring with PTU exposure up to 13 weeks of age, but body weight became comparable among groups by 26 weeks of age. Testicular weight tended to be lower up to 7 weeks but was higher after 13 weeks of age. Epididymis weight was not different among the groups at any age. Plasma concentrations of thyroxine and triiodothyronine in the PTU groups were significantly lower at 3 weeks of age but recovered to normal levels by 26 weeks of age. No dose-related trend in plasma testosterone concentrations was found. Seminiferous tubules were larger at 13 and 26 weeks of age with PTU exposure. The number of Sertoli cells was significantly higher from 3 through 26 weeks of age. The number of Leydig cells was significantly lower up to 7 weeks of age but was comparable among groups from 13 weeks of age onwards. Thus, transient gestational and lactational thyroid hormone suppression induced small testes in early life but led to paradoxical dose-dependent testicular enlargement in adults as indicated partly by larger seminiferous tubules with numerous Sertoli cells in male rat offspring.