Expression of luteinizing hormone/human chorionic gonadotrophin (LH/HCG) receptor mRNA in the human ovary

The gonadotrophins follicle stimulating hormone (FSH) and luteinizing hormone (LH) are key hormones in the regulation of ovarian function. In the present study, the expression of LH/human chorionic gonadotrophin (HCG) receptor mRNAs in the human ovary was examined. Northern blot analysis was used to measure relative amounts of LH/HCG receptor mRNA, and in-situ hybridization was used to localize LH/HCG receptor transcripts. Northern blot analysis of human ovaries detected three transcripts (5.4, 3.6 and 2.4 kb) for the LH/HCG receptor. LH/HCG receptor mRNA concentrations increased from preovulatory follicles to the corpus luteum of the midluteal phase, and decreased at the late luteal phase. Using in-situ hybridization, LH/HCG receptor mRNA was located predominantly in granulosa cells in the same follicle. Cloning of the human LH/HCG receptor cDNA previously revealed the existence of two alternative forms of the receptor differing by the presence (HLH-Ra) and absence (HLH-Rb) of 62 amino acids by exon 9. We have studied the functional significance of these receptor isoforms and have confirmed that they are generated by alternative splicing. A reverse transcription-polymerase chain reaction amplification was used to detect different isoforms of LH receptor mRNAs in ovary and placenta. The expression of the two mRNA forms of LH/HCG receptor were detected in ovary, and at very low concentrations in placenta. Treatment with HCG caused a dose-dependent increase in cAMP production with an initial response evident at approximately 1 ng/ml HCG in COS-7 cells expressing HLH-Ra. However, a complete loss of signal transduction was found in cells transfected with the truncated HLH-Rb.