Circadian rhythms in serum LH, FSH and prolactin levels in adult male rats.

Abstract

In order to elucidate the existence of circadian rhythm in serum LH, FSH and prolactin in male rats, serum LH, FSH and prolactin levels in adult male rats of Holtzman strain were determined at 2-hrs intervals under the light control from 5:00 A.M. to 7:00 P.M. using NIAMD rat LH, FSH and prolactin radioimmunoassay kits.A manifest circadian rhythm was demonstrated in serum LH and FSH levels. Serum LH levels showed the peak at 11:00 P.M. and the minimal level at 5:00 A.M. Serum FSH showed high levels from 7:00 P.M. to 3:00 A.M. in the dark period, then a sharp decline at 5:00 A.M. and remained in low levels during light period (7:00 A.M. to 5:00 P.M.). No circadian rhythm in serum prolactin was observed in adult male rats.These data demonstrate that LH and FSH secretion from the male rat pituitary shows the high values at night or dark time and the low values at day or light time. It is noteworthy that these circadian rhythm in LH and FSH secretion coincides well with the circadian rhythm in sexual behavior of male rats.