BREATHING RESPONSE TO HYPOXIA IN RELATION TO MEASURED PLASMA NEUROMODULATORS DURING POSTNATAL DEVELOPMENT

Abstract

Breathing response to 12 and 6% O₂ in N₂ (in isocapnia) was measured in 1-5 and 19-25 day old acute, anesthetized piglets before and after 3 mg/kg i.v. naltrexone. The degree of interaction between the anesthetic and naltrexone was assessed. At the end of each hypoxic trial, arterial blood was sampled, for measurements of pH and gas tensions, (Met)enkephalin-Arg⁶-Phe⁷, adenosine, noradrenaline and adrenaline. Results show that, as compared to older animals, young piglets (1) have greater degree of ventilatory depression in response to increasing severity of hypoxia; (2) have greater ventilatory responses with naltrexone than without the drug, and (3) demonstrate amelioration or reversal of the biphasic hypoxic response with naltrexone. Furthermore, enkephalin, adenosine, noradrenaline and adrenaline tend to increase during hypoxia in the younger animals. We conclude that, while the central role of catecholamines in respiration is uncertain at present, this study provides further evidence for the possible role of opioid peptides and adenosine in early postnatal hypoxic depression. (Supported in part by the Swedish Medical Research Council and by NIH grant HL36939 (IRM)).

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