Loss of myometrial oxytocin receptors during oxytocin-induced and oxytocin-augmented labour

Oxytocin is used widely for the induction and augmentation of labour, but t here is little information about the dynamics of oxytocin receptors in huma n myometrium during parturition, and the possible effect of oxytocin infusi on. This information is important because G protein-coupled receptors, such as the oxytocin receptor, undergo desensitization after prolonged or repea ted stimulation. The concentration of myometrial oxytocin receptors and the steady state of its mRNA were measured in patients undergoing Caesarean se ctions before or during spontaneous or induced labour. The concentration of receptors before labour was 477 (175-641) fmol mg(-1) protein (median, qua rtile range), and decreased to 140 (72-206; P < 0.05) and 118 (69-75; P < 0 .01) fmol mg(-1) protein during prolonged oxytocin-augmented and oxytocin-i nduced labour, respectively. The corresponding oxytocin receptor mRNA conce ntrations decreased by 60- and 300-fold, respectively. The decrease in rece ptor binding and mRNA in women receiving oxytocin infusion indicates that h omologous receptor desensitization occurs in vivo.