Endothelium-derived hyperpolarization factor (EDHF) is up-regulated in a pig model of acute liver failure

Abstract

Background. Acute liver failure (ALF) is hemodynamically characterized by hyperdynamic circulation, but the pathophysiologic mechanisms underlying these disturbances are not known. The purposes of the present experiments were: to study systemic and peripheral hemodynamics in vivo, to measure changes in vascular reactivity in vitro, and to determine the role of endothelium-dependent vasodilator pathways in a well-validated porcine model of ALF. Methods. Landrace pigs (24–29 kg) were allocated to sham operation (n=8) or ALF induced by hepatic devascularization (n=9). Systemic and regional hemodynamics were monitored. Femoral artery rings were prepared for isometric tension recordings 8 h after ALF induction. Contractile responses to phenylephrine were assessed in ring segments of endothelium-intact femoral arteries in the absence or presence of inhibitors of endothelium-derived hyperpolarizing factor, nitric oxide synthase, cyclooxygenase and heme oxygenase pathways. Results. Pigs with ALF developed a hyperdynamic circulation. Cardiac index increased (P_GT<0.001), while mean arterial pressure (P_GT=0.012) and systemic vascular resistance decreased (P_GT<0.001) in this group. Femoral artery blood flow decreased in controls, while it remained unchanged in ALF (P_GT=0.010). Accordingly, vascular resistance across the hind leg was significantly decreased (P_GT<0.001) in ALF. The combination of Ca²⁺-activated potassium channel inhibitors charybdotoxin and apamin, which block the release of endothelium-derived hyperpolarizing factor, increased the contraction force (ANOVA, P_GT=0.05) and E_max (P = 0.01) to phenylephrine in ALF. In contrast, inhibitors of nitric oxide synthase, cyclooxygenase and heme oxygenase pathways did not increase isometric contraction force. Conclusions. Endothelium dependent hyperpolarization of vascular smooth muscle contributes to the development of hyperdynamic circulation in ALF.

• Hemodynamics
• isometric force
• K⁺ channels
• nitric oxide
• vascular smooth muscle