Journal of Applied Physiology, Vol 55, Issue 4 1311-1320, Copyright © 1983 by American Physiological Society
Enkephalin-induced changes in ventilation and ventilatory pattern in adult dogs
G. G. Haddad, M. R. Gandhi, G. M. Hochwald and T. L. Lai
We studied the changes in ventilation induced by intracisternal
administration of enkephalins in four unanesthetized adult dogs.
Instantaneous minute 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 (5, 25, 60, and 125 micrograms/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. However, naloxone did not
increase VT/TT when injected without prior administration of DAME. We
conclude that 1) the decrease in VT/TT is due to a decrease in respiratory
duty cycle; 2) periodic breathing and increased frequency of sighs
constitute part of the changes in the ventilatory pattern induced by DAME;
3) a ventilatory withdrawal reaction may occur after a receptor-agonist
interaction of short duration; and 4) although enkephalins can modulate
ventilation and the breathing pattern in a major way, these data provide no
evidence suggesting that this modulation is tonic.
