Thyroid hormone synergizes with follicle stimulating hormone to inhibit apoptosis in porcine granulosa cells selectively from small follicles.

To investigate the effect of thyroid hormone on the proliferative activity and apoptosis of granulosa cells at the varying stages of follicular growth, porcine granulosa cells obtained from small (1-2 mm), medium (3-5 mm) and large (6-11 mm) follicles were cultured under a serum-free condition in the presence or absence of follicle stimulating hormone (FSH; 20 ng/ml), with or without triiodothyronine (T3; 10-8M). Relative viability, proliferative activity, and apoptosis of cultured granulosa cells were evaluated with 3-(4.5-dimethylahiazol-2-yl)-2,5-diphenyltetrazolium bromide [MTT] assay, Ki67 expression and activated caspase-3 protein expression, respectively. MTT assay showed that T3 had no significant effect on the relative viability of granulosa cells regardless of the follicle size. Ki67-positive rate in small follicle granulosa cells was augmented by treatment with FSH whereas it was not affected by T3. Furthermore, FSH treatment decreased activated caspase-3 protein-positive rate of small follicle granulosa cells. Relative to the treatment with FSH alone, concomitant treatment with FSH and T3 resulted in further decrease in caspase-3 protein-positive rate in small follicle granulosa cells. Treatment with T3 alone did not affect the caspase-3 protein-positive rate. These results suggest that thyroid hormone synergizes with FSH to inhibit apoptosis in small follicle granulosa cells without affecting the proliferative potential of those cells.