In order to understand the relationship between the
cough and respiratory centers in the brain stem, we investigated the effects of
antitussive drugs such as
codeine,
dextromethorphan,
eptazocine and
fominoben on respiratory movement and the
cough reflex.
Coughs were induced using electrical stimulation of the central cut end of the right superior laryngeal nerve in lightly anesthetized dogs. The drugs were administered intraarterially into the vertebral artery. Rate (RR), amplitude (RA) and volume (RV) of the respiration and number (NC) and amplitude (AC) of the
cough reflex evoked were measured as indices.
Codeine produced a decrease in RR, RV and NC at 0.3 mg and, additionally, AC at 1 mg.
Dextromethorphan increased RR and RV and rather enhanced NC and AC at 0.3 mg, but the agent reduced NC and AC at 3 mg even if it increased RR and RV.
Eptazocine produced decreases in RA, NC and AC at 1 mg, and, additionally, RV
at 10 mg.
Fominoben increased RR, RA and RV dose-dependently at 0.3-3 mg, although it depressed NC and AC at 3 mg. These findings suggest that the thresholds for the
cough responses and respiratory responses to
antitussive drugs are different from
drug to
drug and that the respiratory centers and
cough center in the brain stem are affected in a different manner even qualitatively.