Prostacyclin stimulates relaxin release from cultured porcine luteal cells

The release of relaxin from cultured porcine luteal cells (derived from pregnant sows) was detected by a reverse hemolytic plaque assay. In this assay, luteal cells are cocultured in monolayers with protein-A-coupled ovine erythrocytes. In the presence of porcine relaxin antiserum and complement, a zone of hemolysis--a plaque--develops around relaxin-releasing luteal cells. Treatment with a prostacyclin analogue (carba-prostacyclin; 10 and 100 ng/ml) significantly accelerated the rate of plaque formation in a dose-dependent manner. In contrast, the culture of luteal cells in the presence of cyclooxygenase inhibitors (indomethacin, ibuprofen, and diclofenac sodium) resulted in no change in the rate of basal relaxin release. These results add weight to the view that prostacyclin may contribute alone, or perhaps in combination with other prostanoids, to the overall regulation of ovarian endocrine function and relaxin release during pregnancy in the pig. However, the data are inconsistent with the possibility that prostacyclin arises from relaxin-releasing luteal cells themselves.