Pituitary adenylate cyclase-activating polypeptide acts synergistically with relaxin in modulating ovarian cell function in rats

The interactive effects of pituitary adenylate cyclase-activating polypepti de (PACAP) and relaxin on the secretion of gelatinases, involved in matrix remodeling, in ovarian theca-interstitial cells and granulosa cells, were i nvestigated in gonadotropin-primed immature rats. The gelatinases secreted from cultured cells were analyzed using gelatin zymography and scanning den sitometry. We have previously shown that relaxin stimulated the secretion o f a 71 kDa gelatinase, identified as a type IV collagenase (matrix metallop roteinase 2), in rat theca-interstitial cells. This study has demonstrated that PACAP27 and PACAP38, with similar potency, dose-dependently enhanced r elaxin-induced secretion of 71 kDa gelatinase, whereas PACAP alone had no e ffect. In rat granulosa cells, both PACAP37 and PACAP38 alone dose-dependen tly increased the secretion of a 63 kDa gelatinase. In addition, this study has shown that cAMP signaling pathway mediators act similarly to that of P ACAP on gelatinase secretion in rat ovarian cells. Cholera toxin, forskolin and 8-bromoadenosine cAMP augmented relaxin-induced secretion of 71 kDa ge latinase in theca-interstitial cells, and alone they had no effect. These m ediators also increased the secretion of 63 kDa gelatinase in granulosa cel ls. It is well known that the increase in cellular cAMP level is associated with the morphological rounding-up phenomenon in granulosa cells. This stu dy has shown that PACAP and cAMP pathway mediators, but not relaxin, could cause such changes in cell shape in granulosa cells as well as in theca-int erstitial cells. In conclusion, this study provides original findings that PACAP acts synergistically with relaxin in stimulating the secretion of gel atinases in rat ovarian theca-interstitial cells and granulosa cells. This supports the idea that relaxin and PACAP may serve as ovarian physiological mediators of gonadotropin function in facilitating the ovulatory process. In addition, PACAP appears to act through the cAMP signaling pathway to aff ect biological functions in ovarian cells, whereas relaxin does not.