GnRH receptor mRNA expression by in-situ hybridization in the primate pituitary and ovary

Gonadotrophin-releasing hormone (GnRH) receptors are present on the ovary as well as in the anterior pituitary gland. GnRH analogues may exert their actions in part via these ovarian receptors. However, in the primate ovary, GnRH receptors are of low affinity and their significance is questionable. The aim of the present study was to compare pituitary and ovarian expression of the GnRH receptor mRNA by in-situ hybridization to gain further information on the possible significance of the ovarian receptor. Pituitaries and ovaries were obtained from two stump-tailed macaque monkeys and three marmoset monkeys at the mid-luteal phase of the ovulatory cycle. Human corpora lutea were obtained during the early and mid-luteal phase and after 'rescue' by human chorionic gonadotrophin (HCG) and a whole ovary obtained during the late luteal phase (n = 1 per group). Frozen tissue sections were incubated with a P-33-labelled probe to the human GnRH receptor and exposed for 4 weeks. All pituitary glands exhibited intense silver grains in the anterior pituitary gland. In the ovaries, grains were present at low levels in the granulosa cells of antral follicles, just above tissue background in corpora lutea and indistinguishable from tissue background in the remaining ovarian compartments. These results demonstrate that the GnRH receptor mRNA in the primate pituitary is present in sufficient quantities to be clearly detectable in the anterior pituitary gland by in-situ hybridization. In contrast, in the human and monkey, ovary levels of mRNA appear to be very low.