ENDOCRINE-MEDIATED AND AUTOCRINE-MEDIATED REGULATION OF RAT OVARIAN (THECA-INTERSTITIAL) INTERLEUKIN-1-BETA GENE-EXPRESSION - GONADOTROPIN-DEPENDENT PREOVULATORY ACQUISITION

We, and others have recently demonstrated the ovary to be a site of interleukin-1 (IL-1) reception and action. Since IL-1 is an established mediator of inflammation and since ovulation may constitute an inflammatory-like reaction, consideration was given to the possibility that IL-1 may play an intermediary role in the ovulatory process. To begin to evaluate the above hypothesis, we have set out to evaluate rat ovarian IL-1-beta gene expression, to determine its cellular localization, and to study its modulation by key endocrine and autocrine regulatory signals. To this end, use was made of a solution hybridization/RNase protection assay in which rat ovarian total RNA (20-mu-g) was hybridized with a [P-32]-labeled 272 base rat IL-1-beta antisense riboprobe. To assess rat ovarian IL-1-beta gene expression under in vivo circumstances, use was made of an established experimental model capable of simulating naturally-occurring follicular maturation, ovulation, and corpus luteum formation. Specifically, a single subcutaneous injection of PMSG (15IU/rat) was followed (48h) later by an ovulatory dose (15IU) of human chorionic gonadotropin (hCG). A faint protected fragment 222 bases long corresponding to the IL-1-beta message was detectable in whole ovarian material prior to gonadotropic stimulation. Treatment with PMSG for 48h resulted in a modest, albeit measurable increase in the densitometrically-quantified steady state levels of the ovarian IL-1-beta message. Most striking, however, were the increments noted in the relative abundance of ovarian IL-1-beta transcripts following a 6h exposure to hCG producing a 4 to 5-fold increase (P < 0.05) over the untreated state at a time point approximately 6h prior to projected follicular rupture. Subsequent evaluation of ovarian IL-1-beta transcripts, 24 and 48h following hCG administration, revealed significant (P < 0.05) decrements (relative to the 6h peak) to a level comparable to that seen at the conclusion of 48h of treatment with PMSG. Cellular localization studies revealed the gonadotropin-dependent IL-1-beta mRNA to be theca-interstitial cell-exclusive. To assess rat ovarian IL-1-beta gene expression under in vitro circumstances, we have set out to determine whether IL-1 itself may influence the relative level of its own message. Treatment of whole ovarian dispersates with rhIL-1-beta (10ng/ml) for 4 and 24h resulted in a marked (P < 0.05) time-dependent increase (up to 12-fold) in the relative abundance of IL-1-beta transcripts when compared with untreated controls. Taken together, these observations establish the rat ovarian theca-interstitial cell as a site of IL-1-beta gene expression, the preovulatory acquisition of which is gonadotropin-dependent. In addition, our present findings document the ability of IL-1-beta to exert a positive upregulatory effect on its own expression, an autocrine action potentially concerned with self-amplification. As such, this temporal (potentially self-amplifying) sequence of events provides strong indirect support for the proposal that intraovarian IL-1-beta may play an intermediary role in the preovulatroy developmental cascade.