Tumor necrosis factor alpha inhibits gonadotropin hormonal action in nontransformed ovarian granulosa cells. A modulatory noncytotoxic property

Abstract

It has been suggested that resident ovarian macrophages may play a role in the regulation of ovarian function through local paracrine secretion of regulatory molecule(s). It is the objective of the in vitro studies reported herein to evaluate the potential ovarian relevance of one such macrophage product, tumor necrosis factor alpha (TNF-alpha). To this end, use was made of a primary culture system of rat ovarian granulosa cells, the functional status of which was monitored by the acquisition of estrogen, progestin, and proteoglycan biosynthetic capacity. Whereas treatment with the gonadotropin follicle-stimulating hormone (FSH), a potent functional regulator, resulted in a substantial increase in the extent of aromatization (conversion of androgenic steroid precursors to estrogens), concomitant exposure to TNF-alpha (10 ng/ml) produced significant (p less than 0.05), yet reversible inhibition (71 +/- 7%) of this FSH effect. This specific activity of TNF-alpha was characterized by a projected minimal effective dose of less than 0.1 ng/ml, an apparent median inhibitory dose of 0.56 +/- 0.14 ng/ml, and a minimal time requirement of 48 h. Significantly, the direct effect of TNF-alpha could not be accounted for by a decrease in cellular viability or plating efficiency, nor by a decrease in the number of cells or their DNA content. Instead, TNF-alpha inhibited FSH hormonal action at the level of stimulatable adenylate cyclase activity, exerting no apparent effect either at the level of the FSH receptor or at site(s) of action distal to cAMP generation. The effect of TNF-alpha was not limited to the attenuation of estrogen biosynthesis, exerting qualitatively similar effects on FSH-supported progestin and proteoglycan biosynthetic capacity. As such, these findings are in keeping with the notion that subnanomolar concentrations of TNF-alpha, possibly of ovarian macrophage origin, may comprise the signal of a paracrine loop designed to attenuate gonadotropin action thereby playing a potential role in the development and/or demise of the ovarian follicle.