Analysis of release of porcine relaxin by reverse haemolytic plaque assay: evidence for autoregulation.

Relaxin release from monodispersed luteal cells derived from pregnant pigs (days 100-110 of gestation; n = 3) was detected by a reverse haemolytic plaque assay. In this technique, luteal cells were co-cultured in monolayers with ovine erythrocytes coupled to protein-A. In the presence of porcine relaxin antiserum and complement, a zone of haemolysis--a plaque--developed around relaxin-releasing luteal cells. Luteal cells were preincubated with porcine relaxin (up to 1000 ng/ml) or progesterone (up to 0.5 micrograms/ml) for 18 h before the plaque assay. Relaxin (but not progesterone) pretreatment inhibited subsequent relaxin release. The inhibitory effect of relaxin on its own release (autoregulation) has the potential to be a significant part of the local mechanisms which contribute to the overall control of ovarian secretion of protein hormones.