Peripheral metabolism of testosterone during the annual reproductive cycle in the male hedgehog, a hibernating mammal

Abstract

The seasonal cycle of plasma testosterone levels in hedgehogs of midwestern France shows large variations and different successive sequences: a resting period in autumn, an increase during winter in January, continued high levels from midwinter to midsummer that are characterized by an important spring peak, a regular decrease in May–June, a shorter but regular summer peak, and an involution beginning at the end of summer. To elucidate (i) the increase of plasma testosterone levels in January during hibernation and (ii) the regular decrease of plasma testosterone levels in May–June during the activity period, the seasonal cycles of metabolic clearance and production rates of testosterone were studied, using [3H]testosterone in a single injection technique. The rate of peripheral metabolism of testosterone was reduced in autumn but increased in January during hibernation, simultaneously with the endocrine activity of the testis; it was maximum in February–March, then fluctuated but stayed at a high level during spring and summer, and decreased in September. In these hedgehogs there is a clear annual cycle of testosterone production with two maxima, and only the decrease of plasma testosterone levels observed in June can be explained by an increase of the metabolic clearance rate.