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Inhibitory component in the hyperventilatory response to acute hypoxia in adult rabbits and cats and evidence of participation of endorphins in the underlying mechanism

Gung Meichuen, Hu Shutsu, Huang Shaoyung, Xu Fadi

Shanghai Institute of Physiology, Academia Sinica. Shanghai, China

Abstract

The ventilatory response to acute hypoxia in human adults is different from that of the newborn infants.The adult response is simply a sustained hyperventilation, whereas in the newborn (<7 days) a biphasic response occurs, i. e. a very brief increase in ventilation followed by a prolonged hypoventilation Ill. Similar difference exists in the case of rabbits (<15 days), The inhibitory phase is antagonized by naloxone, implying that the responsible cause of inhibition should be endorphins activity. We hypothesize that similarly in the adult there might be a “concealed” endorphin effected inhibitory component within the overall hypoxic hyperventilatory response. The problem deserves study in view of the greater practical importance of understanding the adult response than that in the newborn period extending only several days. The present study provides experimental evidence that: (1) In both adult awake rabbits and anesthetized cats acute hypoxia gives rise to ventilatory inhibitory activities beside the generally known hyperventilating mechanism of chemoreflexive nature. (2) This hypoxic ventilatory inhibition can be reversed by naloxone injected into blood circulation, suggesting a hypoxiainduced endorphine effect to underlie the inhibitory component of the response. Simple injection of naloxone into circulation during normoxia does not affect ventilation. (3) Naloxone perfused through the fourth ventricle cerebrospinal fluid space also markedly antagonizes the inhibition, indicating that the endorphine effect concerned takes place, at least in part, in the central nervous system.

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Citing This Article：

Gung Meichuen, Hu Shutsu, Huang Shaoyung, Xu Fadi. Inhibitory component in the hyperventilatory response to acute hypoxia in adult rabbits and cats and evidence of participation of endorphins in the underlying mechanism. Acta Physiol Sin 1985; 37 (1): (in Chinese with English abstract).