Effects of adrenomedullin on nitric-oxide production during forebrain ischemia and reperfusion in mice

Abstract

Adrenomedullin(AM)is a vasodilatory hormone secreted mainly by the vascular wall, and its expression is remarkably enhanced after stroke. Several studies have shown that AM inhibits ischemic injury in the brain. The present study investigates the effects of AM on nitric oxide(NO)production during forebrain ischemia and reperfusion. Halothane anesthesia was administered to AM-knockout(AM )and control(C57 BL 6J)mice and then NO production was continuously monitored in the left striatum by in vivo microdialysis. A laser Doppler probe was fixed on the right scalp to measure relative cerebral blood flow(rCBF)continuously. Blood pressure(BP), blood gases and body temperature were monitored and physiologically maintained. After equilibrium for 2 hours, fractions were collected every 10 minutes. Forebrain cerebral ischemia was produced by occluding both common carotid arteries. After 10 minutes, the loops around both common carotid arteries were released. Levels of nitrite and nitrate in dialysates were determined using the Griess reaction. At 6 hours after forebrain cerebral ischemia, the degrees of the ischemic damage in hippocampal CA1 neurons were investigated. Knockout of the AM gene did not affect BP and rCBF. Levels of total NO(nitrite+nitrate) were lower in AM-knockout mice at baseline, during ischemia and after reperfusion. The survival cell rate of hippocampal CA1 neurons in AM-knockout mice was lower than that of control mice. These data suggest that AM exert protective effects by activating NO synthase in the brain during ischemia and reperfusion. (Cerebral Blood Flow and Metabolism 21:1―6,2010)