You are here:
HORMONAL REGULATION OF GONADOTROPIN-RELEASING HORMONE RECEPTORS AND MRNA ACTIVITY IN OVINE PITUITARY CULTURE
Citation:
Sealfon, S., S. Laws, J. Wu, B. Gillo, AND W. Miller. HORMONAL REGULATION OF GONADOTROPIN-RELEASING HORMONE RECEPTORS AND MRNA ACTIVITY IN OVINE PITUITARY CULTURE. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-90/475 (NTIS PB91182154).
Description:
Previous studies demonstrate that gonadotroph responsiveness to GnRH, GnRH binding, and the apparent number of GnRH receptors are all increased by 17B-estradiol (E) or inhibin (IN) in ovine pituitary cultures. rogesterone attenuates these effects. o explore differences between the effects of IN and E on GnRH binding, a detailed time-course was performed. he 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. ombined treatment of IN and 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. o 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. fter 48 h of treatment, IN or E each led to a 7 to 8-fold increase in GnRH receptor mRNA activity. reatment with both hormones led to a 19-fold increase. he increase in mRNA activity induced by either hormone was greatly attenuated by progesterone. odulation of GnRH receptor mRNA levels suggests that IN, E and P regulate responsiveness to GnRH in the ovine pituitary, at least in part, by altering de nova synthesis of GnRH receptors. he differing time-courses of action, as assayed by GnRH binding, and the additivity of effects at the mRNA level, suggest that IN and E may alter mRNA levels via different mechanisms.