Serum concentrations of gonadotrophins and the hypothalamic content of gonadotrophin releasing hormone in male rats exposed to 35 degrees C.

Serum concentrations of FSH and LH and the hypothalamic content of gonadotrophin releasing hormone (GnRH) were measured by radioimmunoassay in male rats maintained at 35 degrees C for various periods of time. The results show that heat exposure caused a temporary decrease in serum concentrations of LH and FSH which was associated with comparable changes in the hypothalamic content of GnRH. Histological examination of the adenohypophysis of rats exposed to heat for 42 days disclosed that the gonadotrophs underwent hypertrophy and hyperplasia and appeared more active than those of control rats. The data suggest that in rats exposed to heat for prolonged periods a new steady-state is established through which an adequate serum level of LH is maintained.