[The regulation of human myometrial oxytocin receptor expression by oxytocin]

Myometrial contraction induced by oxytocin (OT) is dependent on the OT concentration and the number of OT receptors (OTR) expressed. We previously reported that the number of myometrial OTR expressed is regulated by estradiol and progesterone in myometrial cell culture. In the present study, we evaluate the change in the number of OTR expressed on the cell surface after the addition of OT. After OT was added under various conditions to myometrial cells, we measured the number of OTR expressed on the cell surface (surface-OTR) and those in the plasma membrane (PM) (total-OTR). 1. After the addition of 1 nM OT, total-OTR was 25.78 fmol/mg protein in the OT-negative control and was 23.66 and 7.88 at 30 minutes and 24 hours. 2. Surface-OTR showed no changes after the addition of 1 nM OT at 4 degrees C, and the value after 60 minutes was 8.90 fmol/mg protein. At 37 degrees C, however, it become 5.53 and 1.72 fmol/mg protein 60 minutes after the addition of OT at 10pM and 10nM. This decrease in surface-OTR was suppressed by concanavalin A (ConA), which inhibits the internalization of receptors. Our study demonstrated that OTR expressed on the surface of myometrial cells decreased rapidly in the presence of OT due to internalization.