Gap junctions and hydrogen peroxide are involved in endothelium-derived hyperpolarising responses to bradykinin in omental arteries and veins isolated from pregnant women

Abstract

Altered endothelial function may underlie human cardiovascular diseases, including hypertension, diabetes and pre-eclampsia. While much is known about endothelial function in small arteries, very little is known about endothelial responses in small veins isolated from humans. Therefore, we assessed endothelium-dependent responses in omental arteries and veins isolated from healthy pregnant women, focussing on endothelium-dependent hyperpolarising (EDH) mechanisms. Human omental arteries and veins were obtained from women undergoing elective caesarean sections and examined using pressure myography. In pressurised vessels, the effects of proposed inhibitors of EDH production/function were examined on responses to bradykinin. The expression of connexins Cx37, 40 and 43 was assessed using immunohistochemistry. Bradykinin caused vasodilatation in human pressurised omental arteries and veins. In both vessels, responses to bradykinin were partially blocked in the presence of the gap junction uncoupler, carbenoxolone, and reduced further with the addition of catalase, which acts to degrade H2O2. The effect of catalase alone was more pronounced in venous preparations. All three connexins were expressed in both arteries and veins, with a similar distribution pattern, where Cx37 and Cx40 were located mainly in the endothelium and Cx43 located mostly in the media. These data show that, in human omental vessels, an EDH mechanism is produced in response to bradykinin that involves gap junction communication and the production of H2O2. These mechanisms may be involved in the haemodynamic alterations that take place during pregnancy, and any aberration in their function could contribute to raised blood pressure in hypertensive disorders of pregnancy, such as pre-eclampsia.