Effects of Short Photoperiod on the Ability of Golden Hamster Ptuitaries to Secrete Prolactin and Gonadotropins in Vitro 1

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Abstract
Transfer of male golden (Syrian) hamsters from a 14L:10D (light:dark) to a 5L:19D photoperiod induced significant changes in pituitary function tested in vitro. Within 27 days after transfer to a 5L:19D photoperiod, basal prolactin (Prl) release was significantly depressed and response to dopamine (DA) was significantly enhanced as compared to Prl release by pituitaries from 14L:10D hamsters. FSH release tended to be depressed after 9 or 27 days of 5L:19D exposure, but the effect was not significant. After 77 days of 5L:19D exposure, Prl release was further suppressed, while FSH release surpassed that seen in 14L:10D pituitaries. In vitro FSH response to LHRH was also enhanced at this time. After 15 wk of exposure to a short photoperiod, FSH secretion was still elevated above control levels, but Prl release and Prl response to DA were no longer different from that of 14L:10D controls. Secretion of luteinizing hormone (LH) in vitro, either basal or LHRH-stimulated, was not affected by photoperiod at any time tested. Short photoperiod exposure does not reduce the pituitary''s ability to secrete LH or FSH, although secretion of Prl is severely attenuated.