The role of endothelium-derived hyperpolarizing factor in the regulation of the uterine circulation in pregnant rats

Objective: The purpose of this study was to determine whether endothelium-derived hyperpolarizing factor regulates rat uterine circulation in pregnant rats. Study Design: Intact isolated uterine vascular beds from late pregnant rats were perfused in situ with Krebs buffer that contained dextran, indomethacin, N-nitro-L-arginine methyl ester, and phenylephrine. Endothelium-derived hyperpolarizing factor–induced decreases in perfusion pressure in response to acetylcholine were analyzed. Results: The decrease in perfusion pressure induced by endothelium-derived hyperpolarizing factor was significantly attenuated by 4-aminopyridine and was abolished by a combination of 4-aminopyridine and tetraethylammonium. Endothelium-derived hyperpolarizing factor–induced decrease in perfusion pressure was abolished by potassium chloride and attenuated by miconazole, but not linoleyl hydroxamic acid. Endothelium-derived hyperpolarizing factor–induced decrease in perfusion pressure persisted after perfusion with solutions that contained 2 inhibitors of nitric oxide synthase and a scavenger of nitric oxide. Nitric oxide exerted negative feedback on the endothelium-derived hyperpolarizing factor effects. Conclusion: In the pregnant rat uterine vascular beds, endothelium-derived hyperpolarizing factor release is activated by a delayed rectifier type of voltage-sensitive potassium channel. Endothelium-derived hyperpolarizing factor does not seem to be related to nitric oxide or to products of lipoxygenase or cytochrome p450 mono-oxygenase pathways of arachidonic acid metabolism. (Am J Obstet Gynecol 2001;185:638-42.)