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Calcitonin Expression in Rat Anterior Pituitary Gland Is Regulated by Ovarian Steroid Hormones

Department of Pharmaceutical Sciences, Texas Tech University Health Sciences Center, Amarillo, Texas 79106

Address all correspondence and requests for reprints to: Girish V. Shah, Ph.D., Texas Tech University Health Sciences Center, Department of Pharmaceutical Sciences, 1300 Coulter, Amarillo, Texas 79106. E-mail: girish{at}ama.ttuhsc.edu.

Gonadotroph-derived calcitonin-like peptide (pit-CT) is a potent inhibitor of lactotroph function. We investigated the effect of ovarian hormones on pit-CT mRNA expression in the anterior pituitary (AP) gland of cycling female rats. Levels of mRNAs for pit-CT, CT receptor, prolactin (PRL), and ß-LH during 4-d estrous cycle were determined. In a second study, the effects of estrogens and progesterone on pit-CT and PRL mRNA levels were investigated. In a third group, the effect of estrogen or progesterone depletion on pit-CT mRNA expression was studied. In a fourth group, the effect of passive pit-CT immunization on PRL and LH mRNA expression was examined. Pit-CT mRNA levels varied during estrous cycle. They were highest in diestrus, but lowest in the evening of proestrus. CT-receptor mRNA levels displayed smaller fluctuations. Estrogen repletion caused a decline in pit-CT mRNA expression in ovariectomized rats, but progesterone produced a marked increase. ICI 182,780 prevented the decline of pit-CT mRNA levels during late proestrus-estrus, but RU 486 attenuated pit-CT mRNA levels. Passive CT immunization in diestrus altered PRL and LH mRNA expression, and advanced the estrus cycle. These results suggest that pit-CT mRNA expression is regulated by ovarian hormones, and depletion of pit-CT advances their estrous cycle.

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