TROPHIC ACTION OF RELAXIN ON PORCINE THECA CELLS - INTERACTIONS WITH INSULIN AND INSULIN-LIKE GROWTH-FACTOR-I IN-VITRO

Relaxin, a product of porcine preovulatory theca cells, has been found to stimulate granulosa cell deoxyribonucleic acid (DNA) synthesis and proliferation in vitro. Whether relaxin has a similar trophic effect on porcine theca cells if unknown. The objective of this study was to determine the role of relaxin alone or in combination with other membe rs of the insulin-like family of hormones on theca cell DNA synthesis and cell proliferation in vitro. The studies showed that insulin (1-10 00 ng/ml) and insulinlike growth factor (IGF-I; 1-30 ng/ml) stimulated DNA synthesis in a dose-dependent manner in theca cells. Relaxin (10 and 100 ng/ml) alone produced a twofold increase in [H-3]thymidine inc orporation into theca cell DNA. Nerve growth factor, another member of the insulinlike hormone family, failed to influence [H-3]thymidine in corporation by theca cells at any stage of follicle development. Relax in significantly enhanced the effects of insulin and IGF-I on [H-3]thy midine incorporation by theca cells (P<0.05). Relaxin antiserum suppre ssed relaxin-induced DNA synthesis, but had no effect on either contro l or IGF-I-induced DNA synthesis indicating that the antiserum inhibit ion was not due to nonspecific cytotoxic effects. After a 6 day exposu re to relaxin in vitro, there was a dose-dependent increase in prolife ration of theca cells from small follicles which ranged from 1.5 to tw ofold. These results suggest that locally-produced relaxin, alone or t hrough interaction with insulin and IGF-I, may play an important role in theca cell growth during porcine follicle development.