Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C11
Investigating the Physiology of Diabetic Pregnancies - Myometrial Contractility and the Effects of Insulin
A. M. Heath1, F. Dawood2, S. Wray1
1. Cellular and Molecular Physiology, Institute of Translational Medicine, Univerisity of Liverpool, Liverpool, United Kingdom. 2. School of Reproductive and Developmental Medicine, University of Liverpool, Liverpool, United Kingdom.
Worldwide, a significant number of diabetic pregnancies end up in caesarean sections (CS). We have examined whether insulin the main control for diabetes, may have an effect on the contractility of myometrium and the pathway of insulin action in the uterus. Methods - The effects of insulin (7pM- 700nM) on spontaneous and oxytocin (1nM) stimulated contractility in myometrial strips from term diabetic and non diabetic women (with full consent) and 22day pregnant Wistar rat were examined. In some experiments intracellular Ca signals were simultaneously measured. Ouabain (Na pump inhibitor) or tetraethylammonium (K channel inhibitor) was added to contracting myometrium combined with insulin to examine the mechanism of insulins action. To examine the expression of IRβ immunohistochemistry and western blotting was used. Results- Insulin causes a dose dependent decrease in myometrial contractions in pregnant rats and both diabetic and non diabetic women, which was mirrored in the underlying calcium transients. In non diabetics the decrease was significant (p=<0.05) at concentrations of 70pM-700nM, where as in diabetics the decrease was only significant at the higher concentrations of 70nM-700nM. At the highest concentration of insulin (700nM) the decrease in force in non diabetics was significantly greater than diabetics (21.67±10.67% n=15, 42.20±9.73% n=10 respectively)relative to control period. In the presence of oxytocin, addition of insulin also decreased the force of myometrial contractility: in non diabetics this was significant(p=<0.05) for all concentrations,however the decreases were not significant in diabetics. The results of the immunohistochemistry showed a significant reduction (p=<0.01)in the amount of IRβ expressed in the myometrium of diabetics compared to non diabetics(13.9 ± 1.6 %(n=8), 21.4 ±1.8%(n=8)respectively), which was confirmed by western blotting. When 10µM Ouabain was added to contracting myometrium in combination with increasing concentrations of insulin, the negative effect of insulin on contractility was inhibited for all concentrations. 5mM TEA also significantly inhibited the negative effect of insulin on myometrial contractility. Conclusions - Insulin causes a dose-dependent decrease in amplitude of spontaneous and oxytocin stimulated contractions in human and rat myometrium. The decrease in calcium transients suggests that insulin is acting by decreasing calcium currents, and may partially stimulate the Na pump resulting in cell hyperpolarisation.The inhibitory effect of TEA on myometrial responses to insulin suggests insulin may also impede conductance of K+. The inhibitory effect of insulin on myometrial contractility was reduced in diabetics compared to non diabetics. This may be due to the significant decrease in the expression of IRβ in the myometrium from diabetics compared to non diabetics,which we found.
Where applicable, experiments conform with Society ethical requirements