The first breaths of air stimulate noradrenaline turnover in the brain of the newborn rat

Lagercrantz, H., Pequignot, J., Pequignot, J.‐M. & Peyrin, L. 1992. The first breaths of air stimulate noradrenaline turnover in the brain of the newborn rat. Acta Physiol Scand144, 433–438. Received 19 July 1991, accepted 3 December 1991. ISSN 0001–6772. Department of Paediatrics (KS), Karolinska Institute, Stockholm, Sweden and UA CNRS 1196, Physiologie, Faculté de Médecine, Université Claude Bernard, Grange Blanche, Lyon, France. The aim of this study was to analyse the noradrenaline (NA)‐turnover in the brain around birth and its significance for neonatal adaptation. NA and its metabolite 3–methoxy‐4–hydroxyphenylethylene glycol (MHPG) have been measured by high‐pressure liquid chromatography (HPLC) in the pons‐medulla and cortex in rat foetuses and pups. The MHPG/NA ratio was used as an index of NA‐turnover. Catecholamines were also determined in the adrenals for comparison. The MHPG/NA ratios were found to increase 2.7–fold in the pons‐medulla and 2–fold in the cortex during the first day after birth. The surge of NA‐turnover occurred after the pups had been breathing air for two hours. The increase of NA‐turnover was significantly lower in the cortex of rat pups breathing a hypoxic gas mixture or when they were kept in a cooler environment. The differences were less marked in the pons‐medulla. We conclude that breathing air stimulates NA‐turnover in the brain of the newborn rat and this stimulatory effect is modulated by environmental factors.