THE EFFECTS OF SHORT PHOTOPERIOD, BLINDING AND THE PINEAL GLAND ON PROLACTIN IN THE SYRIAN HAMSTER (STALK-MEDIAN, EMINENCE, DOPAMINE, HYPOTHALAMIC).
AuthorORSTEAD, KEVIN MICHAEL.
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PublisherThe University of Arizona.
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AbstractThe physiological effects of the pineal gland on the prolactin cells of the adenohypophysis were examined in short photoperiod-exposed male hamsters, as well as in blinded male and female hamsters. Pituitary storage of prolactin was assessed by monitoring radioimmunoassayable prolactin levels in the pituitaries in vivo and the total amount of immunoreactive prolactin in vitro. The effects of the pineal on prolactin secretion were estimated by measuring immunoassayable prolactin titers in the serum. Prolactin synthesis was measured by the ability of anterior pituitaries to incorporate ³H-leucine into prolactin in vitro. Finally, the effects of blinding and the activated pineal on hypothalamic hypophysiotrophic activity was assessed by incubating pituitaries in the presence of neutralized, acidic extracts of the stalk-medium eminence (SME) region of the mediobasal hypothalamus. In the male hamster, the pineal gland inhibits PRL cell function which encompasses reductions in the synthesis, storage and release of prolactin. The depressions in prolactin release and in pituitary storage are evident as early as three weeks after males are deprived of light. However, the inhibitory influence of the pineal on prolactin synthesis may be only partially apparent by eight to nine weeks after male hamsters are deprived of light, and is not fully evident until 12 weeks of light restriction. In the blinded female hamster, the synthesis, storage and release of prolactin are also markedly suppressed. However, all aspects of prolactin cell inhibition in the female may not be pineal-mediated. Furthermore, it appears that there may be some direct hypothalamic mechanism by which orbital enucleation inhibits prolactin cell function that is independent of the pineal gland. Based on the data presented in this dissertation, it is concluded that the SME region of the female hamster contains inhibitory activity which may be specifically responsible for the inhibition of prolactin synthesis. Furthermore, blinding and the pineal gland may independently exert rather specific influences upon hypophysiotrophic activity within the SME region of the female hamster.