Gonadotropin-releasing hormone receptor messenger ribonucleic acid expression in rat ovary

Rat GnRH pituitary receptor complementary DNA was used to isolate a truncated clone from a rat corpus luteum complementary DNA library that proved to be identical in sequence to the rat anterior pituitary GnRH receptor. The distribution of the GnRH receptor messenger RNA (mRNA) was then determined in rat ovary using in situ hybridization. GnRH receptor expression was investigated in cyclic female rats and in hypophysectomized immature female rats treated with either recombinant human FSH or human menopausal gonadotropin. The expression of LH receptor mRNA was determined in serial sections as an index of the health and differentiation of the follicles. In cyclic animals, GnRH receptor mRNA was detected in granulosa cells at varying stages of follicular development and in the corpus luteum. Ovaries from hypophysectomized animals expressed GnRH receptor mRNA in the granulosa cells of most follicles. The administration of FSH or human menopausal gonadotropin to hypophysectomized animals altered the distribution of GnRH receptor mRNA. During antral development, the signal was most abundant in medium-sized follicles not expressing LH receptor mRNA and showing signs of follicular atresia. However, healthy preovulatory follicles also expressed GnRH receptor mRNA. We conclude that the expression of the GnRH receptor gene in granulosa cells is 1) individually regulated for each follicle, 2) persists in the corpus luteum, and 3) expressed in atretic follicles.