The rat intraovarian interleukin (IL)-1 system: cellular localization, cyclic variation and hormonal regulation of IL-1β and of the type I and type II IL-1 receptors

An increasing body of evidence supports the possibility that intraovarian interleukin (IL)-1 plays an intermediary role in the periovulatory cascade. To gain further insight into the intraovarian IL-1 hypothesis, we studied the cellular localization cyclic variation and hormonal regulation of IL-1β, as well as of the type I and type II IL-1 receptors (IL-1R) in immature rats. In situ hybridization localized IL-1β and type I IL-1R transcripts to the granulosa cell compartment, the innermost layers of the theca interna and to the oocyte of the untreated immature ovary. Molecular probing of whole ovarian material in the course of a simulated estrous cycle revealed a progressive preovulatory increase in IL-1β and type I IL-1R transcripts to an in vivo peak at the time of ovulation (3.0- and 2.5-fold increases over untreated controls; P<0.05). Comparable efforts to localize and probe for type II IL-1R transcripts failed to elicit a detectable signal. The basal in vitro expression pattern of IL-1β and type II IL-1R transcripts by whole ovarian dispersates revealed an early (4 h) spontaneous increase to a peak (2.1- and 5.8-fold increases over time 0; P<0.05) followed by a gradual decline to a 48 h nadir. Treatment of whole ovarian dispersates with the IL-1 receptor antagonist (IL-1RA) or with IL-1β failed to alter the initial (4 h) burst of IL-1β or of type II IL-1R expression thereby suggesting IL-1-independence. Treatment with hCG proved equally ineffective. However, longer-term treatment of whole ovarian dispersates with IL-1β produced a significant secondary increase (5.9-fold over time 0; P<0.05) in IL-1β (but not type II IL-1R) transcripts by 48 h. This IL-1 effect was completely blocked by co-treatment with IL-1RA thereby suggesting mediation via a specific IL-1 receptor. Qualitatively comparable but quantitatively reduced results obtained for isolated granulosa cells. The basal in vitro expression pattern of type I IL-1R transcripts by whole ovarian dispersates revealed a progressive spontaneous increase (3.1-fold increase overall) over the 48 h culture. Treatment with IL-1β produced a significant (P<0.05) increase (5-fold) in type I IL-1R transcripts by 48 h, an effect which was completely blocked by co-treatment with IL-1RA. Taken together, these observations: (1) localize IL-1β and its type I receptor to granulosa cells, the innermost layers of the theca interna and to the oocyte; (2) confirm their periovulatory in vivo expression pattern; (3) document their expression by untreated cultured whole ovarian dispersates; and (4) demonstrate their in vitro responsiveness to receptor-mediated/IL-1-driven autocrine amplification. The type II IL-1R was undetectable in vivo, its in vitro expression pattern proving IL-1- and hCG-independent. The periovulatory expression pattern of IL-1β and its receptor (type I) is compatible with the notion that the intraovarian IL-1 system may play an intermediary role in the ovulatory process.