Direct Effects of Hormones of the Hypothalamic-Pituitary-Thyroid Axis on Testicular Steroidogenesis in Hamsters

Abstract

Hormones of the hypothalamic-pituitary-thyroid axis have been shown to influence testicular function in rodents directly or indirectly. Panke et al. (1978) reported that experimental induction of hypo- or hyperthyroidism in the rat led to reductioms in plasma testosterone and in testicular LH receptors without altering peripheral concentrations of LH, FSH or PRL. There is a well known relationship between hypo- and hyperthyroidism, and fertility disorders in both men and women (Ingbar, 1985). Vriend and Wasserman (1986) showed that the thiourea-induced increase in TSH can partially reverse the short-photoperiod related testicular regression in Syrian hamsters. Furthermore, in genetically hypothyroid mice in which thyroid hormones are absent and plasma TSH levels are extremely high, Leydig cell responsiveness to hCG in vivo is significantly increased by TSH (Amador et al., 1986). Moreover, specific receptors for both TSH and thyroid hormones have been detected in rodent testes (Oppenheimer et al., 1974; Davies et al., 1978). Therefore, the present study was designed to study the effects of TRH, TSH, calcitonin (CTH) and thyroid hormones in vitro on testicular steroidogenesis in Syrian and Siberian hamsters.