Abstract: 24

LONG-R³-ILGF-I PREVENTS ESTROGEN-INDUCED REDUCTION OF PROGESTERONE SYNTHESIS IN CULTURED OVINE GRANULOSA CELLS FROM SMALL FOLLICLES.

Willem. S. Pretorius^{1 *}, Willem. A. Coetzer¹ , Danie M. Barry^{1 *}
Department of Human and Animal Physiology, University of Stellenbosch, Stellenbosch, South Africa ¹

Estrogen (E₂) is luteolytic during the first 5 days of the estrous cycle in the ewe despite the fact that it is considered a mitogenic hormone. Very high levels of E₂ have been implicated as the cause of premature luteal regression in the superovulated ewe. Up to now it was assumed that E₂ induces luteal regression via the up-regulation of oxytocin receptors, resulting in the release of a luteolytic amount of prostaglandin F₂ (PGF₂). Premature luteal regression, however, presents some characteristics that are not found in PGF₂ induced regression, including the occurrence of ovaries with both normal functioning and regressed corpora lutea. The question arises if E₂ always exerts its luteolytic action via PGF₂, or can it cause luteolysis by acting directly on luteal cells. We used in vitro culture of granulosa cells studying the direct effects of E₂ on luteal cells in the absence of PGF₂. Results have shown that E₂ can cause a reduction in progesterone production in granulosa cells cultured from small follicles (< 5 mm in diameter) but not in granulosa cells from larger follicles (> 5 mm in diameter) (P< 0.001). This effect could be prevented by the administration of Long-R³-insulin like growth factor-I (long-R³-ILGF-I) to cultures (P< 0.001). It was found that granulosa cells from larger follicles lack estrogen receptors (ER) after 6 days of culture in vitro while granulosa cells from small follicles still have ER present. Long-R³-ILGF-I treated granulosa cells from small follicles lacked ER. Thus we concluded that Long-R³-ILGF-I prevented E₂ induced reduction in progesterone synthesis, by down regulating ER.

    This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.