Effects of Hypoxia-Ischemia and Inhibition of Nitric Oxide Synthase on Cerebral Energy Metabolism in Newborn Piglets

Abstract

The present study was designed to examine the effects of inhibition of nitric oxide synthase on cerebral energy metabolism after hypoxia-ischemia in newborn piglets. Ten 1- to 3-d-old piglets received N(omega)-nitro-L-arginine (NNLA), an inhibitor of nitric oxide synthase (NNLA-hypoxia, n = 5), or normal saline (hypoxia, n = 5) 1 h before cerebral hypoxia-ischemia. After the infusion, hypoxia-ischemia was induced by bilateral occlusion of the carotid arteries and decreasing FiO2 to 0.07 and maintained for 60 min. Thereafter, animals were resuscitated and ventilated for another 3 h. Using 1H- and 31P-magnetic resonance spectroscopy, cerebral energy metabolism was measured in vivo at 15-min intervals throughout the experiment. Phosphocreatine to inorganic phosphate ratios decreased from 2.74 +/- 0.14 to 0.74 +/- 0.36 (hypoxia group) and 2.32 +/- 0.17 to 0.18 +/- 0.10 (NNLA-hypoxia group) during hypoxia-ischemia. Thereafter, phosphocreatine to inorganic phosphate ratios returned rapidly to baseline values in the hypoxia group, but remained below baseline values in the NNLA-hypoxia group. Intracellular pH decreased during hypoxia-ischemia and returned to baseline values on reperfusion in both groups. Intracellular pH values were lower in the NNLA-hypoxia group (p < 0.001, ANOVA). Lactate was not present during the baseline period. After hypoxia-ischemia, lactate to N-acetylaspartate ratios increased to 1.34 +/- 0.28 (hypoxia group) and 2.22 +/- 0.46 (NNLA-hypoxia group). Lactate had disappeared after 3 h of reperfusion in the hypoxia group, whereas lactate to N-acetylaspartate ratios were 1.37 +/- 1.37 in the NNLA-hypoxia group. ANOVA demonstrated a significant effect of NNLA on lactate to N-acetylaspartate ratios (p < 0.001). Inhibition of nitric oxide synthase by NNLA tended to compromise cerebral energy status during and after cerebral hypoxia-ischemia in newborn piglets.

Neuroprotection by Selective Nitric Oxide Synthase Inhibition at 24 Hours After Perinatal Hypoxia-Ischemia

“…43 The positive outcome in some studies with the use of nonselective NOS inhibitors might be caused by the rather mild endothelial NOS inhibitory properties of the compound used. 29 In earlier studies it was shown that 2-iminobiotin is a reversible inhibitor of both the neuronal and the inducible isoforms of NOS but not the endothelial NOS isoforms. 5 In 3 additional piglets we tested the effect of 2-iminobiotin treatment on physiological parameters.…”

“…29,30 It has been shown that pretreatment with 7-nitroindazole, a selective neuronal NOS inhibitor, suppressed both peaks of NO metabolites (during hypoxiaischemia as well as on reperfusion) and provided neuroprotection in a 7-day-old rat model of hypoxia-ischemia. 4,31 This is in agreement with the results in a middle cerebral artery occlusion (MCAO) model in mice and rats, in which neuronal NOS inhibition before the onset of hypoxia-ischemia reduced the infarct volume.…”

Effects of Selective Nitric Oxide Synthase Inhibition on IGF-1, Caspases and Cytokines in a Newborn Piglet Model of Perinatal Hypoxia-Ischaemia

“…An arterial line was inserted in the right femoral artery for continuous registration of blood pressure and blood gas analysis. After regaining haemodynamic stability, the piglets were subjected to 1 h of hypoxia-ischaemia by occlusion of both carotid arteries with hypoxia, controlled by frequent 31 P-MRS measurements as previously reported [12]. Briefly, 31 P-MR spectra were made continuously during hypoxia-ischaemia until severe energy failure was evident, defined as a reduction in the phosphocreatine/inorganic phosphate (PCr/Pi) ratio to at least 30% of baseline values for minimally 45 min [13].…”

Neuroprotective Effect of <i>L</i>-Arginine in a Newborn Rat Model of Acute Severe Asphyxia

“…The variable effect of NO seems to depend on several factors as the amount of NO, the isoform or cellular location of NO synthase (NOS) and on the redox state of NO or NO derived species [2] . NO exerts its toxic effect by increasing oxidative stress -mainly through peroxynitrite generation -, inhibiting oxidative phosphorylation as well as mitochondrial respiration and glycolysis, damaging DNA and increasing cellular energy expenditure [2][3][4][5] . In an in vivo model of HIE in neonatal rats, two peaks of NO metabolites are detected in the damaged side of brain, the fi rst one during hypoxia and the second one during the reoxygenation period [6,7] .…”