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LOCAL CONTROL OF CIRCULATION

The mechanism of EDHF-mediated responses in subcutaneous small arteries from healthy pregnant women

Department of Obstetrics and Gynecology, Karolinska Institutet, Huddinge University Hospital, Stockholm, Sweden 14186

Submitted 23 September 2003 ; accepted in final form 28 January 2004

We studied the importance of endothelium-derived hyperpolarizing factor (EDHF) vs. nitric oxide (NO) and prostacyclin (PGI₂) in bradykinin (BK)-induced relaxation in isolated small subcutaneous arteries from normal pregnant women. We also explored the contribution of cytochrome P-450 (CYP450) product of arachidonic acid (AA) metabolism, hydrogen peroxide (H₂O₂), and gap junctions that have been suggested to be involved in EDHF-mediated responses. Isolated arteries obtained from subcutaneous fat biopsies of normal pregnant women (n = 30) undergoing planned cesarean section were mounted in a wire-myography system. In norepinephrine-constricted vessels, incubation with N^G-nitro-L-arginine methyl ester (L-NAME) resulted in a significant reduction in relaxation to BK. Simultaneous incubation with L-NAME and indomethacin failed to modify this response further. BK-mediated dilatation in the presence of K⁺-modified solution was decreased to similar level as obtained after incubation with L-NAME. Incubation with L-NAME abolished BK-induced responses in K⁺-modified solution. Sulfaphenazole, a specific inhibitor of CYP450 epoxygenase, and catalase (an enzyme that decomposes H₂O₂) did not affect the EDHF-mediated relaxation because concentration-response curves to BK were similar in arteries after incubation with L-NAME vs. L-NAME + sulfaphenazole and L-NAME + catalase. The inhibitor of gap junctions, 18-glycyrrhetinic acid, significantly reduced BK-mediated relaxation both without and with incubation with L-NAME. We found that both NO and EDHF, but not PGI₂, are involved in the endothelium-dependent dilatation to BK. BK-induced relaxation is almost equally mediated by NO and EDHF. CYP450 epoxygenase metabolites of AA or H₂O₂ do not account for EDHF-mediated response; however, gap junctions are involved in the EDHF-mediated responses to BK in subcutaneous small arteries in normal pregnancy.

endothelium-dependent relaxation; gap junctions; endothelium-derived hyperpolarizing factor; hydrogen peroxide

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