Nitric oxide and nitric oxide synthase in the early phase of perinatal asphyxia of the rat

The role of nitric oxide, a compound involved in neurotransmission and regu lation of cerebral blood flow, in cerebral ischemia is still not fully eluc idated yet. Although well studied in adult systems of cerebral ischemia/hyp oxia, information on nitric oxide in perinatal asphyxia is limited and, in particular, no direct evidence for its generation has been provided. We the refore decided to study nitric oxide generation in brain of asphyctic rat p ups by biophysical and biochemical methods. We used a simple, non-invasive rat model resembling the clinical situation in perinatal asphyxia: rat pups delivered by Caesarean section were placed into a water bath at 37 degrees C still in patent membranes for various asphyctic periods (up to 20 min). Brain pH, cerebral blood flow, neuronal nitrix oxide synthase messenger RNA (by northern and dot blot analysis), immunoreactive protein (by western bl ot analysis) and nitric oxide synthase activity were determined; generation of nitric oxide was evaluated directly by electron paramagnetic resonance spectroscopy. Neuronal nitric oxide synthase messenger RNA activity and nit ric oxide generation were unaffected, whereas neuronal nitric oxide synthas e-immunoreactive protein of 150,000 mel. wt was decreased and of 136,000 me l. wt was increased with the length of the asphyctic period. This is the fi rst report on direct evidence for the generation of nitric oxide in perinat al asphyxia and we demonstrate that nitric oxide production remains unaffec ted even by 20 min of asphyxia, at a time-point when cerebral blood how was increased four-fold and severe acidosis was present. However, it was found that levels of immunoreactive neuronal nitric oxide synthase of 136,000 me l. wt were increased paralleling the length of asphyxia. Levels of the 150, 000 mel. wt immunoreactive neuronal nitric oxide synthase protein decreased , suggesting a different regulation pattern. Thus, the present biochemical and biophysical results form the basis for fu rther investigations on nitric oxide in perinatal asphyxia. (C) 1999 IBRO. Published by Elsevier Science Ltd.