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, but not thromboxane, responsiveness in pregnant human myometrium during labour
School of Pharmacy, University of Bradford, West Yorkshire BD7 1DP, UK1 Bradford Royal Infirmary, Duckworth Lane, Bradford, West Yorkshire BD9 6RJ, UK2 Department of Biological Sciences, Allergan Inc., Irvine, California, 92612 USA
(Correspondence should be addressed to K M Marshall; Email: k.m.marshall{at}bradford.ac.uk)
Prostaglandins (PG) E2, PGF2
and thromboxane (TX) mediate uterine contractility by targeting prostonoid EP, FP and TP receptors respectively. The aim of this study was to elucidate the function of these receptors in isolated human myometrium taken at term gestation prior to and following labour onset. Lower segment myometrial strips were immersed in organ baths in oxygenated Krebs' solution at 37 °C and connected to isometric force transducers. After equilibration, spontaneous activity and concentration responses to PGE2, PGF2
and U46619
[GenBank]
(a stable TX mimetic) were measured as area under the curve and expressed as a percentage of the final contraction induced by hypotonic shock. Results were expressed as arithmetic means±S.E.M. and analysed using two-way ANOVA with Bonferroni's post hoc test. Myometrium excised at late gestation displayed the greatest spontaneous activity compared with the tissues taken during labour (P<0.001). Excitation evoked by PGF2
(P<0.01) and PGE2 at 10–5 mol/l were attenuated after labour onset. U46619
[GenBank]
consistently stimulated concentration-dependent contractions (P<0.001) and selective antagonists confirmed TP-mediated effects. The maintained responses to TX indicate crucial roles for TP receptors in the muscular tonus of the parturient uterus. This receptor and its secondary messenger system represent effective myometrial targets for tocolytic agents in both pregnancy and labour-associated disorders.
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