The biocellular effect of thyroid hormone on functional differentiation of porcine granulosa cells in culture

Abstract

To elucidate if the thyroid hormone acts directly on the ovary, the biocellular effect of L-thyroxine (T4) on porcine granulosa cells cultured in vitro was investigated. Monolayer cultures of porcine granulosa cells obtained from small (1 approximately 2 mm), medium (3 approximately 5 mm) or large (6 approximately 11 mm) follicles were carried out in the presence of porcine FSH (100 ng/ml). Concomitant treatment with T4 promoted FSH-dependent morphological luteinization, i.e. alteration of immature granulosa cells obtained from small follicles to epithelioid form. T4 also increased FSH-stimulated induction of hCG/LH receptor on immature granulosa cells. Furthermore, T4 augmented FSH-mediated production of progesterone and estradiol by immature granulosa cells cultured in vitro. The concentration of T4 to produce the maximal stimulatory effect was 10-7 M, demonstrating that optimal concentration of thyroid hormone is required for the expression of this stimulatory action. Since T4 alone demonstrated no effect on the differentiation of porcine granulosa cells and all the stimulatory effect of T4 seems to have a permissive action on FSH-induced granulosa cell luteinization. Although insulin showed a similar effect on porcine granulosa cells, no stimulation of estradiol production by porcine granulosa cells was observed with insulin in the culture system used in this study. These results suggest that the thyroid hormone acts directly on the ovary and plays an important role in modifying the FSH-dependent cellular differentiation of immature granulosa cells.