||Hormonal Regulation of Gonadotropin-Releasing Hormone Receptors and Messenger RNA Activity in Ovine Pituitary Culture.
Sealfon, S. C. ;
Laws, S. C. ;
Wu, J. C. ;
Boaz, G. ;
Miller, W. L. ;
||Health Effects Research Lab., Research Triangle Park, NC. ;Mount Sinai School of Medicine, New York. Dept. of Neurology. ;North Carolina State Univ. at Raleigh. Dept. of Biochemistry.;National Institutes of Health, Bethesda, MD.;Department of Agriculture, Washington, DC.
||EPA/600/J-90/475; NIH-HD-10773 ;USDA-86-CRCR-1-2181;
Gonadoliberin receptors ;
Messenger RNA ;
Pituitary gland ;
Cultured cells ;
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Previous studies demonstrate that gonadotroph responsiveness to GnRH, GnRH binding, and the apparent number of GnRH receptors are all increased by 17 beta-estradiol (E) or inhibin (IN) in ovine pituitary cultures. Progesterone attenuates these effects. To explore differences between the effects of IN and E on GnRH binding, a detailed time-course was performed. The results indicate that after 48 h IN had a greater effect on binding of a GnRH agonist (5-fold increase) than E (3-fold increase), but was slower to act initially. A combined treatment of IN and E gave a partially additive effect at 48 h (6.5-fold increase). The mechanism of receptor regulation in this system is not known, but could involve synthesis, recycling, or modification of GnRH receptors. To investigate the contribution of altered receptor biosynthesis to the regulation of receptor levels, a functional Xenopus oocyte-based assay for GnRH receptor mRNA activity was employed. After 48 h of treatment, IN or E each led to a 7 to 8-fold increase in GnRH receptor mRNA activity. Treatment with both hormones led to a 19-fold increase. The increase in mRNA activity induced by either hormone was greatly attenuated by progesterone. (Copyright (c) 1990 by The Endocrine Society.)