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Endogenous Opioids and Ventilatory Adaptation to Prolonged Hypoxia in Goats,
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA
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To investigate whether endogenous opioid peptides mediate time-dependent changes in arterial PCO2 and ventilatory responsiveness during prolonged hypoxia, we studied four goats at rest during 14 days in a hypobaric chamber. Arterial PCO2 fell during the first several hours of hypoxia and then remained stable over the next 7 days. By day 14, PaCO2 rose somewhat, and ventilatory responsiveness to CO2, while still greater than normal, was less than that observed over the first week of hypoxia. Immunoactive beta-endorphin levels in plasma and CSF did not change during the 14-day period. Administration of naloxone on day 14 did not restore the ventilatory response to CO2 to the level observed during the early phase of acclimatization. We conclude that, in goats 1 time-dependent changes in resting arterial PCO2 during acclimatization to prolonged hypoxia are associated with reciprocal changes in the ventilatory response to CO2 and 2 these changes in resting PaCO2 and ventilatory responsiveness are not associated with or attributable to alterations in endogenous opioid peptide levels in plasma or CSF.
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