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Desensitization of oxytocin receptors in human myometrium
S Phaneuf1, G Asbóth, M P Carrasco
1Nuffield Department of Obstetrics and Gynaecology, University of Oxford, Women's Centre, John Radcliffe Hospital, UK. sylvain.phaneuf@imsu.ox.ac.uk
Abstract:
In the present study, we investigated the possible mechanisms by which oxytocin might regulate oxytocin receptor (OTR) density. Exposure of cultured myometrial cells to oxytocin for a prolonged period caused desensitization: the steady-state level of oxytocin binding was 210 x 10(3) binding sites/cell, but this was time-dependently reduced to 20.1 x 10(3) sites/cell by exposing the cells to oxytocin for up to 20 h. In contrast, Western blotting data showed that the total amount of OTR protein was not affected by oxytocin treatment for up to 24 h. Flow cytometry experiments demonstrated that OTRs were not internalized during this treatment. However, RNase protection assays and Northern analysis showed that in cultured myometrial cells OTR mRNA was reduced by oxytocin treatment to reach a new low steady-state concentration. Analysis of this mRNA in myometrial biopsies from 17 patients undergoing emergency Caesarean section showed how it decreased with advancing labour. Samples obtained after 12 h of labour contained approximately 50 times less OTR mRNA than samples obtained from patients in labour for less than 12 h. We speculate that this decrease in OTR mRNA represents in-vivo OTR desensitization.
Insights
Prolonged oxytocin exposure reduces oxytocin receptor (OTR) density by decreasing OTR mRNA levels, not protein amount or internalization. This mechanism may explain OTR desensitization during labor.
Area of Science:
- Reproductive biology
- Molecular endocrinology
Background:
- Oxytocin plays a crucial role in uterine contractions.
- Oxytocin receptor (OTR) density is critical for myometrial responsiveness.
- Mechanisms regulating OTR density are not fully understood.
Purpose of the Study:
- To investigate the mechanisms underlying oxytocin's regulation of OTR density in myometrial cells.
- To determine if oxytocin affects OTR protein levels, internalization, or mRNA expression.
- To examine OTR mRNA levels in relation to labor progression.
Main Methods:
- Primary cultured human myometrial cells were treated with oxytocin.
- Oxytocin binding assays were performed to measure OTR density.
- Western blotting assessed OTR protein levels.
- Flow cytometry evaluated OTR internalization.
- RNase protection assays and Northern blot analyzed OTR mRNA expression.
- Myometrial biopsies from patients undergoing Cesarean section were analyzed for OTR mRNA.
Main Results:
- Prolonged oxytocin exposure led to a significant time-dependent decrease in OTR binding sites, indicating desensitization.
- Oxytocin treatment did not alter total OTR protein levels or cause OTR internalization.
- Oxytocin significantly reduced OTR mRNA levels in cultured myometrial cells.
- Analysis of myometrial biopsies revealed a substantial decrease in OTR mRNA with advancing labor duration.
Conclusions:
- Oxytocin-induced OTR desensitization in myometrial cells is primarily mediated by a reduction in OTR mRNA levels.
- This downregulation of OTR mRNA, rather than changes in protein or internalization, appears to be the key regulatory mechanism.
- The observed decrease in OTR mRNA with advancing labor suggests a role in in-vivo OTR desensitization during childbirth.