In Situ Hybridization Study of Gonadotropin-Releasing Hormone (GnRH) Receptor mRNA in Female Rat Pituitary Gland during Estrous Cycle and after Ovariectomy.

Abstract

Expression of rat GnRH receptor mRNA in female rat pituitary was examined by in situ hybridization using 35S-labeled antisense RNA probe. Specific signals were detected in the pars distalis. For detailed analysis of the cellular expression of GnRH receptor mRNA, the pituitaries were double-stained by in situ hybridization of GnRH receptor mRNA and antisera against some pituitary hormones (LH, FSH, TSH and prolactin). The expression of GnRH receptor mRNA was detected in all the immunoreactive gonadotropes, but was not detectable in TSH or prolactin cells. Cellular expression of GnRH receptor mRNA in immunoreactive gonadotropes was compared during the estrous cycle and after ovariectomy. In the pituitary of normal cycling rats, the mean value of the cellular expression of the mRNA in estrus was significantly smaller than those of other phases of the cycle. In ovariectomized rats, the cellular expression was significantly in-creased 4 days after the operation as compared with normal cycling rats, and the elevated level of cellular expression was maintained until 21 days after ovariectomy. These results suggest that GnRH receptor expression in the pituitary is preferentially localized in gonadotropes, and the extent of cellular expression varies during the estrous cycle and after ovariectomy.