Enkephalin-induced changes in ventilation and ventilatory pattern in adult dogs

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Abstract
The changes in ventilation induced by intracisternal administration of enkephalins in 4 unanesthetized adult dogs. Instantaneous min ventilation (VT/TT) decreased markedly after D-Ala-Met-enkephalinamide (DAME). Mean VT/TT decreased maximally by 20-50 min after DAME and lasted an additional 15-60 min; by 2 h, VT/TT had returned to base line. Four doses 15, 25, 60 and 125 .mu.g/kg) of DAME were used, and the ventilatory response depended on the dose. Mean inspiratory time decreased but mean expiratory time and mean TT showed a marked prolongation. Periodic breathing (2-3 breaths separated by long apneic pauses) occurred in every study and the frequency of sighs increased considerably. All these ventilatory changes were reversed by low doses of naloxone or naltrexone; in addition, VT/TT increased well above base line after the administration of these antagonists. Naloxone did not increase VT/TT when injected without prior administration of DAME. The decrease in VT/TT is due to a decrease in respiratory duty cycle; periodic breathing and increased frequency of sighs constitute part of the changes in the ventilatory pattern induced by DAME; a ventilatory withdrawal reaction may occur after a receptor-agonist interaction of short duration; and although enkephalins can modulate ventilation and the breathing pattern in a major way. No evidence suggesting that this modulation tonic was provided.

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