Endocrine Abstracts

Prostaglandin E (EP) receptors have been characterised in human myometrium from non-pregnant and pregnant (non-labouring) donors (Senior et al. 1991; 1993). However. the response to PGE₂ in tissue taken at labour has not been investigated. The aim of the present study was to compare myogenic activity and the effects of PGE₂ in myometrium from donors at different stages of the menstrual cycle and at pregnancy (labouring and non-labouring).

Human myometrial samples taken at hysterectomy were obtained from the fundus and from the lower section during caesarean. All women gave informed. written consent. Myometrial strips were set up in organ baths containing oxygenated Krebs solution at 37 °C. After 1.5 hours equilibration. spontaneous activity was measured over 30 minutes via force transducers linked to Powerlab and chart software. Vehicle or PGE₂ (10⁻⁹M to 10⁻⁵M) was added cumulatively to organ baths at 30-minute intervals and the responses were measured for 30 minutes. These were expressed as a percentage of the hypotonic shock induced at the end of the experiment by infusing distilled water. Results were analysed using a one-way ANOVA with post-hoc Tukey’s test.

Samples taken during the follicular stage exhibited the greatest myogenic activity compared to tissue collected at luteal (p<0.05) and menstrual (p<0.001) stages and tissue taken at term from pregnant. non-labouring donors (p<0.001). Myogenicity in tissue from non-labouring donors was greater than that from donors in first stage labour. second stage labour and during preterm labour (p<0.001). In myometrium taken at each stage of the menstrual cycle and at term pregnancy PGE₂ inhibited myogenic activity until a concentration of 10⁻⁵M was reached when some stimulation was seen. In tissue taken during labour only inhibitory effects were observed. This indicates that. despite the presence of EP-receptors which mediate excitation. uterine quiescence predominates under these experimental conditions.