PARENT SESSION
Follicular Development

DYNAMIC REGULATION OF OVARIAN INHIBIN IN THE SIBERIAN HAMSTER.

Rainey, Hilary¹, Bernard, Daniel¹, Horton, Teresa¹, Woodruff, Teresa¹, ¹

ABSTRACT- The Siberian hamster reproductive axis responds to changes in day length to permit fertile cycles during seasons conducive to offspring survival. FSH rises in response to increasing day length and is necessary for the re-establishment of normal reproductive function in Siberian hamsters transferred from an inhibitory photoperiod (short; 6 hours of light (L): 18 hours of dark (D) to a stimulatory photoperiod (long; 16L: 8D). The initial rise in FSH is followed by testicular growth and sperm production in male Siberian hamsters and resumption of ovulatory cycles in female Siberian hamsters. In other species, FSH stimulates the production of inhibins A and B, gonadally-derived proteins, which inhibit the production of pituitary FSH. To determine whether gonadal inhibin responds to FSH in female Siberian hamsters we measured inhibin in peripheral circulation in long-day and short-day photoperiod animals, localized inhibin subunit mRNA in specific follicle compartments, and assessed inhibin protein production by the ovary maintained under different conditions of light and dark stimulus. Circulating inhibin levels were low to undetectable in all hamsters regardless of the day length. However, mature and precursor forms of inhibin were detected in ovaries from animals housed under both photoperiods. To test the hypothesis that FSH regulates inhibin production in the Siberian hamster, we injected exogenous gonadotropin (PMSG) into female Siberian hamsters and measured ovarian inhibin production. Ovarian inhibin subunit mRNA and protein were stimulated by gonadotropin within 12 h, and the protein was detected in peripheral circulation by 24 h following hormone administration. The inverse relationship between inhibin and FSH is similar to that present in other species and is likely important to the regulation of successive estrous cycles in the female Siberian hamster. This work was supported by NIH grant PO1 HD21921.

KEY WORDS: activin, reproduction, TGF, FSH