Effects of Transforming Growth Factor-β on the Production of Immunoreactive Insulin-Like Growth Factor I and Progesterone and on [3H]Thymidine Incorporation in Porcine Granulosa Cell Cultures*

Abstract

Transforming growth factor-.beta. (TGF.beta.) has been reported to enhance many FSH-stimulated functions in rat granulosa cell cultures. We, therefore, investigated the actions of TGF.beta. on cultured porcine granulosa cells. We evaluated the production of immunoreactive insulin-like growth factor I (iIGF-I) and progesterone in short term (3-day) and in longer term (7-day) cultures using porcine TGF.beta.1 (pTGF.beta.1). TGF.beta. had a biphasic effect on epidermal growth factor (EGF)-stimulated iIGF-I production in short term cultures. A modest stimulatory effect wsas apparent at 10 pg/ml; however, this end point was completely inhibited by 1-10 ng/ml. TGF.beta. also had a slight stimulatory effect on basal iIGF-I production at 1 pg/ml but not at higher levels. In longer term cultures TGF.beta. did not have a significant effect on either basal or FSH-stimulated iIGF-I production. In both short and longer term culture TGF.beta. markedly inhibited basal and FSH-stimulated progesterone production. We also evaluated the effects of TGF.beta. on the incorporation of [3H]thymidine into DNA and found that basal and growth factor-stimulated (3H]thymidine incorporation were inhibited. No stimulatory effects of TGF.beta. on progesterone production or [3H]thymidine incorporation could be detected over the dose range tested (1 pg/ml to 10 ng/ml). The effects of human TGF.beta.1 and pTGF.beta.2 were compared with those of pTGF.beta.1 on basal and EGF-stimulated [3H]thymidine incorporation. Efects of the peptides were qualitatively similar, but pTGF.beta.2 was somewhat less inhibitory to EGF-stimulated [3H]thymidine incorporation than pTGF.beta.1. The present studies show that in contrast to the well documented stimulatory actions of TGF.beta. in cultured rat granulose cells, this growth factor is a predominantly negative regulator of porcine granulosa cells. With the exception of a modest stimulation of iIGF-I production at very low doses, the effecs of TGF.beta. were to potently inhibit both growth and differentiated function. The inhibitory nature of TGF.beta. should not be overlooked when considering the possible role of this peptide in ovarian development and differentiation.