Seasonal variations of plasma gonadotropin, prolactin, and testosterone levels in primary and secondary hypogonadism: evidence for an independent testicular role.

BACKGROUND: Seasonal hormonal rhythmicity of the hypothalamic-pituitary-gonadal axis may influence reproductive and sexual activity in mammals. AIM: To investigate whether pituitary-gonadal axis secretion seasonality occurs in men with primary and secondary hypogonadism and whether a hierarchical machinery regulates these variations. SUBJECTS AND METHODS: Six adult males with Klinefelter's syndrome (KS), eight with idiopathic normosmic hypogonadotropic hypogonadism (HH) and ten sex- and age-matched healthy controls were studied longitudinally for one year. Every three months, three plasma samples for assay of testosterone, LH, FSH, and prolactin were drawn and the mean value was used for statistical analysis.
RESULTS: Healthy males showed a significant seasonality in LH (zenith in spring) and testosterone (zenith in autumn) but not in FSH and prolactin concentrations. Patients with KS and those with HH showed a seasonal rhythmicity only of testosterone values, even if with small amplitude, with the zenith in spring and summer respectively.
CONCLUSION: The lack of dependence of testosterone on gonadotropin variations in normal men and the persistence of seasonal testosterone but not gonadotropin variations both in primary and secondary hypogonadism seem to indicate a possible independent testicular regulation of this seasonality. The shift of testosterone peak in hypogonadal men with respect to controls suggests that LH variations could play a synchronizing, rather than pace-making, role in seasonal testosterone variations. Since hormonal seasonality may also influence gonadal activity in humans, replacement therapy in hypogonadism should be aimed also at restoring a normal seasonal rhythmicity of pituitary-gonadal hormone concentrations.