Tumor necrosis factor or regulates collagenolytic activity in preovulatoryovine follicles: Relationship to cytokine secretion by the oocyte-cumulus cell complex

The pleiotropic cytokine tumor necrosis factor (TNF)-alpha has been implica ted in the mechanism of ovulation, Experiments were designed to test the hy pothesis that TNF-alpha secreted from the oocyte-cumulus cell complex stimu lates follicular collagenase production and thereby contributes to ovarian wall degradation and ovulatory rupture. Proestrous ewes were treated with G nRH to synchronize the onset of the gonadotropin surge; ovulation occurs ap proximately 24 h later. There was an increase in TNF-alpha (immunoassay) in antral fluid of preovulatory follicles at 18 h after GnRH, which was relat ed to tissue collagenolytic bioactivity (radiolabeled type I substrate dige stion by enzymatic extract) and collagen (hydroxyproline) depletion. Intraf ollicular injection of TNF-alpha antibodies at 12 h after GnRH negated the rise in follicular collagenolytic bioactivity (and is known to block ovulat ion in the sheep), Moreover, collagenase production was enhanced when folli cular tissues (0 h GnRH) were incubated (6 h) with recombinant TNF-alpha; t his effect was abolished by the transcriptional inhibitor actinomycin D, Se cretion of TNF-alpha by oocyte-cumulus cell complexes isolated from preovul atory follicles simulated the in vivo circumstance, Immunostaining indicate d that TNF-alpha was confined mainly to the oocyte before GnRH administrati on, accumulated in cumulus cells during the mid-to-late preovulatory period , and was expended with the imminent approach of ovulation, To our knowledg e, this is the first report specifying that up-regulation of collagenase ex pression is a target mode of TNF-alpha action in preovulatory follicles. Th e oocyte-cumulus cell complex is an apparent source of soluble TNF-alpha.