Effects of hypoxia and reoxygenation with 21% and 100%-oxygen on cerebral nitric oxide concentration and microcirculation in newborn piglets

Bioelectric sensors for continuous registration of nitric oxide (NO) concen trations in tissues provide a new tool for invasive measurement of this gas eous molecule. This study sought to validate cerebral NO measurements using an amperiometric sensor. A series of experiments in 1- to 3-day-old piglet s was carried out to study the response of NO and microcirculation during h ypoxia (FiO2 0.06) and reoxygenation with 100% and 21% oxygen. Two-channel laser Doppler flowmetry was performed in the forebrain cortex. Significant decreases of NO levels were observed immediately after induction of hypoxem ia (p < 0.05). During reoxygenation with 21 or 100% O-2 for 30 min, NO incr eased significantly compared to the values at the end of hypoxia (p < 0.05) . The increase of NO levels in the 100% oxygen group was greater than the i ncrease in the 21% oxygen group (p < 0.05). There were no Significant diffe rences between the two groups during the following 3.5 h of observation. A significant increase in CBF was found in the first 2 min of hypoxia (p < 0. 05), it then continued to fall to values significantly lower than baseline values at the end of hypoxemia (p < 0.05). During reoxygenation CBF normali sed and there were consistent but no Significant differences between the tw o reoxygenation groups. We conclude that NO concentration decreased during the course of hypoxia. Hypoxia-induced cerebral hyperaemia occurred in spit e Of significantly lower NO concentrations. Reoxygenation with 21 or 100% O -2 restored CBF in both groups similarly, although values were higher after reoxygenation with 100% O-2 compared to air. In fact, reoxygenation with 1 00% O-2 led to supranormal levels of NO by contrast to 21% O-2.