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The influence of hypothyroidism on testicular steroidogenesis was investigated by evaluating the production of testosterone and its precursors by isolated testes from adult male rats. Animals were made hypothyroid starting from the 4th week of life either by daily oral administration of 0.1% methimazole (MMI) or by surgical thyroidectomy (TZ). Half of the thyroidectomized rats were i.p. injected with 3 gamma T3/100 g body weight on alternate days during the last three weeks before sacrifice. Hypothyroidism is associated with a severe retardation of body growth, which appears more marked in thyroidectomized than in MMI treated rats; no significant variations in testis weight are observed. Administration of T3 does not completely restore body weight. A significant decrease in the "in vitro" production of testosterone and its precursors by testes isolated from hypothyroid rats is observed. This effect is more evident in thyroidectomized rats where a marked drop in the "in vitro" production of some testosterone delta 4 precursors is associated with the increase in DHEA/delta 4 ratio. T3 injection to thyroidectomized rats only partially restores the "in vitro" testosterone production. Results suggest that as the degree of hypothyroidism became more severe, the rate of testosterone production decreases and testicular steroidogenesis changes from the delta 4 to delta 5 metabolic pathway as a consequence of the impairement of 3-beta-ol-dehydrogenase activity.

Progesterone, 17-hydroxyprogesterone, androstenedione, 5 alpha-dihydrotestosterone, dehydroepiandrosterone, testosterone and oestradiol concentrations in the plasma were measured by simultaneous radioimmunoassay in males of the lizard Podarcis s. sicula. Hormonal determinations were performed at monthly intervals from January to December (except for August). Testosterone and androstenedione reached peak values of 174.8 ng/ml and 21.4 ng/ml in the mating season (spring) and then testosterone fell abruptly to 5.9 ng/ml in June remaining at this level during hibernation when dehydroepiandrosterone (DHA) reached a maximal level of 28.5 +/- 9.3 ng/ml. Castration resulted in a marked decrease of testosterone, androstenedione, dihydrotestosterone and DHA values, with DHA being significantly lowered only during the winter season. In castrated animals, however, testosterone and androstenedione persisted conspicuously in the plasma during the breeding period, suggesting that adrenal sex steroid output may change during the annual reproductive cycle. In intact animals, progesterone and oestradiol exhibited peak values during the refractory period after the mating season. We suggest a probable role of oestradiol in the induction of the refractory period in this lizard.