It is known that the mammalian ovary possesses a complete interleukin-1 (IL-1) system replete with ligands, receptors, and a receptor antagonist. To further assess the hypothesis that IL-1 may play an intermediary role in gonadotropin-triggered ovulation, we have set out to determine whether IL-1 is capable of promoting ovarian collagenase biosynthesis, an established component of the ovulatory cascade. Untreated cultured whole ovarian dispersates from immature (25 day old) rats constitutively elaborated several collagenolytic species as assessed in a gelatin matrix. A major 72 kilodalton (kDa) gelatinase (GL) was particularly apparent. Treatment with IL-1 beta produced selective dose- and cell density-dependent increments in the accumulation of a 92-kDa GL species. Administration of an IL-1 receptor antagonist neutralized the IL-1-induced stimulation of the 92-kDa GL in a dose-dependent fashion thereby supporting the presumption that the IL-1 effect is receptor mediated. Studies of comparable cellular densities of granulosa or enriched theca-interstitial cultures demonstrated the IL-1 induced 92-kDa GL to be highly expressed in the enriched theca-interstitial but not in the isolated granulosa cell preparations. Treatment with transforming growth factor-beta 1, a putative regulator of IL-1 action, significantly attenuated IL-1-induced 92-kDa GL accumulation thereby suggesting a potential regulatory paracrine/autocrine role for this agent in ovarian gelatinase economy. Initial characterization revealed the 92-kDa GL species to be a metalloproteinase present in its proenzyme zymogenic form. Taken together, our present findings reveal the ovarian expression of a constitutive 72-kDa GL and of an IL-1-stimulated 92-kDa GL the accumulation of which is particularly marked in enriched theca-interstitial preparations. These observations, along with the demonstration of the gonadotropin-dependent preovulatory induction of ovarian IL-1 gene expression, provide strong indirect support for the view that IL-1 may be the centerpiece of an intraovarian regulatory loop concerned with the promotion of the ovulatory cascade.