Submission Number: KOJ-4-12-5

Abstract Number: 328

DYNAMIC CHANGES IN MRNAS ENCODING INHIBIN/ACTIVIN SUBUNITS AND FOLLISTATIN IN THE OVARY DURING THE RAT ESTROUS CYCLE.

Koji Y Arai ¹, Kenichi Ohshima ², Gen Watanabe* ², Katsuhiko Arai ¹, Kohkichi Uehara ¹ and Kazuyoshi Taya* ²

Department of Tissue Physiology, Tokyo University of Agriculture and Technology, Tokyo, Japan ¹
Laboratory of Veterinary Physiology, Tokyo University of Agriculture and Technology, Tokyo, Japan ²

Abstract:
To elucidate the quantitative changes in ovarian inhibin/activin subunit and follistatin mRNAs during the rat estrous cycle, levels of these mRNAs were measured by ribonuclease protection assay using digoxygenin labeled RNA probes. Rats were killed at various time of the estrous cycle, and ovaries were collected for isolation of total RNA. Trunk blood samples were also collected to measure plasma concentrations of ovarian hormones. Inhibin alpha subunit mRNA remained at constant levels through estrus, metestrus, and diestrus, and abruptly increased in the morning on proestrus, and then rapidly decreased concomitant with the primary gonadotropin surge. A similar pattern was observed in changes in inhibin/activin beta A subunit mRNA levels. On the other hand, the different pattern was observed in changes in inhibin/activin beta B subunit mRNA levels. Inhibin/activin beta B subunit mRNA remained at constant levels during metestrus and diestrus, and abruptly decreased concomitant with the primary gonadotropin surge. Thereafter, beta B subunit mRNA levels quickly recovered from the nadir by 1100 h on estrus. Changes in plasma concentrations of inhibin A and inhibin B were parallel to ovarian inhibin/activin beta A and beta B mRNA levels respectively with 3-6 h delays. Follistatin mRNA expression was at low levels from the midnight on metestrus to the midnight on diestrus, and then increased until the initiation of the primary gonadotropin surge. Thereafter, follistatin mRNA decreased, and reached the nadir at 0200 h on estrus. Afterward, follistatin mRNA abruptly increased in the morning on estrus, and maintained at high levels until the morning on metestrus. These results suggest that inhibin/activin beta A mRNA is mainly expressed in antral follicles, while inhibin/activin beta B mRNA is mainly expressed in developing follicles in the cyclic rat. Further, changes in follistatin mRNA levels preceded to changes in plasma concentrations of progesterone, suggesting that ovarian follistatin modulates progesterone secretion. This work was supported by US-Japan cooperative Research Grant from the Japan Society for Promotion of Science.

Keywords: inhibin, follistatin, mRNA, ovary, rat, estrous cycle

This abstract is being presented at: 8:00 AM in session:
Gonadal Function