COOLING AND ASPHYXIA DIFFERENTIALLY AFFECT AUGMENTED NORADRENALINE TURNOVER IN THE BRAIN OF THE EXTERNALIZED RAT FETUS

The object was to investigate the effect of various perinatal conditio ns particularly cooling and asphyxia on the noradrenaline INA) turnove r in the foetal rat brain. The ratios between the noradrenergic metabo lite 3-methoxy-4-hydroxy phenyl-ethylene glycol-sulphate (MHPG) and no radrenaline were determined as indexes oi NA-turnover in the cortex an d the pons-medulla of the foetal rat brain using high pressure liquid chromatography (HPLC). Rat foetuses were externalized by caesarean sec tion performed on a spinally anaesthesized highly pregnant rat mother. One uterine horn was used as control while the other was exposed to e xternalization, simulated uterine contractions, cooling or asphyxia. E xternalization per se and simulated uterine contractions did not cause any significant change in the NA-turnover. Cooling at 25 degrees C fo r 20 min caused a significant increase in NA-turnover in the cortex wh ile a significant decrease was observed after 10 min oi asphyxia in bo th the cortex and the pons-medulla and after 15 min in the cortex. We conclude that externalization and simulated uterine contractions per s e do not seem to affect the augmented NA-turnover at birth. Cooling ca used an increase suggesting a potentiating role on NA-turnover in conj unction with the externalization. On the other hand NA-turnover was de pressed by asphyxia, suggesting that the level of oxygen is important for NA neuron activity.