Hypoxia does not increase CSF or plasma beta-endorphin activity.

Abstract

The ability of moderate (30-50 Torr arterial PO2) and severe (less than 30 Torr arterial PO2) hypoxia to generate endogenous opioids that modulate ventilation was studied in unanesthetized goats. Ventilation and its components, arterial blood gas tensions and pH, and plasma and cerebrospinal fluid (CSF) beta-endorphin activity were measured before and after 4 h of sustained moderate or severe hypoxia. Ventilation, as expected, increased with hypoxia. There were no significant changes in either plasma or CSF beta-endorphin activity after sustained hypoxia. To rule out elaboration of endogenous opioids other than beta-endorphin after hypoxia, naloxone or saline was administered to five of the seven goats exposed to 4 h of severe hypoxia, and their ventilatory responses were compared for 30 additional min of hypoxic breathing. No significant differences in ventilation occurred in the two treatment groups during this time period. We conclude that, unlike increases in airway resistance, moderate and severe hypoxia do not cause the elaboration of endogenous opioids that modify respiratory output in unanesthetized adult goats. The apparent ability of hypoxia to cause elaboration of endogenous opioids in the neonate may represent a maturational phenomenon.