Cyclic changes in messenger RNAs encoding inhibin/activin subunits in the ovary of the golden hamster (Mesocricetus auratus)

To elucidate changing patterns of inhibin/activin subunit mRNAs in the ovary of the golden hamster (Mesocricetus auratus) during the oestrous cycle, inhibin/activin subunit cDNAs of this species were cloned and ribonuclease protection assay and in situ hybridization were carried out. Inhibin -subunit mRNA was localized in granulosa cells of primary, secondary, tertiary and atretic follicles throughout the 4-day oestrous cycle. It was also expressed in luteal cells on days 1 (oestrus), 2 (metoestrus) and 3 (dioestrus). A-subunit mRNA was localized in granulosa cells of large secondary (>200 µm) and tertiary follicles throughout the oestrous cycle. B-subunit mRNA was confined to granulosa cells of large secondary and tertiary follicles. Both - and A-subunit mRNAs were also found in ovarian interstitial cells and theca interna cells of tertiary and atretic follicles in the evening of day 4 (pro-oestrus). A striking increase in A-subunit mRNA levels was also observed during the preovulatory period. The expression pattern of A-subunit mRNA during the preovulatory period is unique and not found in other species. An i.v. injection of anti-luteinizing hormone-releasing hormone (LHRH) serum before the LH surge abolished the expression of - and A-subunit mRNAs in ovarian interstitial cells and theca interna cells. The treatment also abolished the preovulatory increase in A-subunit mRNA. Furthermore, administration of human chorionic gonadotrophin (hCG), which followed the injection of anti-LHRH serum, restored the expression patterns of - and Asubunit mRNAs. The present study revealed that the golden hamster showed a unique expression pattern of A-subunit mRNA in response to the LH surge.