Serum levels of gonadotrophins in hamsters exposed to short photoperiods: effects of adrenalectomy and ovariectomy.

Female hamsters rendered acyclic by exposure to short photoperiods (10 h light: 14 h darkness) showed diurnal surges of both LH and FSH which persisted after removal of the ovaries and adrenal glands. The reduced increase in gonadotrophin secretion after ovariectomy, typical of hamsters exposed to short days, was also not contingent upon the presence of the adrenal glands. The results demonstrate that 'supersensitivity' of the neuroendocrine axis to feedback of ovarian or adrenal steroids cannot fully account for either the daily surges of gonadotrophins or the diminished response of LH and FSH to ovariectomy in hamsters maintained on short days. It is suggested that these changes result instead from other pineal-mediated actions of short photoperiods upon the brain.