Naloxone decreases the duration of primary apnea with neonatal asphyxia

Naloxone, a specific opiate antagonist with no agonist properties, in doses of 0.4 and 4.0 mg/kg was found to markedly reduce the duration of primary apnea in asohyxiated newborn rabbits. There was no effect on the duration of the hyperpneic phase (time to primary apnea) or on survival time (time to last gasp). It is suggested that endogenous opiate-like peptides are released during asphyxia and are the major factor in the suppression of medullary inspiratory neuronal discharge during primary apnea. Speculation: Apnea is a serious problem in the asphyxiated newborn infant, the pre-term infant and has been implicated in the sudden infant death syndrome. It is tempting to speculate that endogenous opiate-like peptides prolong primary apnea in these conditions but further studies are reguired. It is also possible that naloxone should be used in the resuscitation of the asphyxiated neonate whether or not the mother has received exogenous opiates; this hypothesis could be tested in appropriate animal models. Endorphins and enkephalins are recently discovered polypeptides with opiate-like activity found in the pituitary gland and in various areas of vertebrate brain, including the medulla, in association with opiate receptors (3,7,8,17). They have been implicated as neurotransmitters involved in the control of pain, emotional behavior and narcotic addiction. We postulated that since exogenous opiates modify respiration and the ventilatory response to hypercapnia and hypoxemia (19), the endogenous opiate-like compounds might modify the respiratory response to neonatal asphyxia. We now report that naloxone, a specific opiate antagonist known to block opiate receptor sites (15), markedly decreases the duration of primary apnea produced by asphyxia in the newborn rabbit.