Evidence for photosensitive regulation of prolactin secretion in prepubertal bulls.
Changing daily exposure of prepubertal bulls from 8 hr of light: 16 hr of dark (8L:16D) to 16L:8D or 6L:8D:2L:8D increased basal secretion of prolactin 418% 6 weeks later. When daily exposure was changed from 8L:16D (6 weeks) to 6L:14D:2L:2D (6 weeks), basal secretion of prolactin increased only 173%. Among photoperiod exposures, prolactin released into blood after injection of 33 micrograms/100 kg body weight of thyrotropin-releasing hormone paralleled the changes described for basal conditions. There was no repeatable diurnal secretory pattern for secretion of prolactin. The data support the hypothesis that cattle possess a photosensitive rhythm for secretion of prolactin.
D000818:Animals; D002417:Cattle / Q000502:physiology*; D008027:Light; D008297:Male; D011388:Prolactin / Q000378:metabolism*; D012636:Secretory Rate / Q000528:radiation effects; D012741:Sexual Maturation
D011388:Prolactin