Effects of castration and thyroidectomy on the annual biological cycles of the edible dormouse Glis glis.

The annual cycle of hibernation, body weight, and plasma testosterone and thyroxine levels were compared in 7 orchidectomized and 16 intact dormice under natural conditions, and in 21 thyroidectomized and 23 intact dormice exposed to a 12-hr light and 12-hr darkness photoperiod under natural temperatures. Hibernation was not affected by either orchidectomy or thyroidectomy, nor did thyroidectomy alter the annual body weight cycle, which, however, was obliterated by orchidectomy. As regards endocrine cycles, orchidectomy had no significant effects on the annual thyroxine cycle, whereas thyroidectomy obliterated the annual testosterone cycle, which was replaced by short-lived, infradian plasma thyroxine cycles. As the latter resembled the fluctuations previously observed in intact animals exposed to constant ambient temperatures, it is proposed that in edible dormice, the annual thyroid cycle, which is thermoperiodically entrained, in turn entrains the testosterone cycle.