Journal of Applied Physiology, Vol 61, Issue 5 1677-1685, Copyright © 1986 by American Physiological Society
Dose-response curves of central and peripheral airways to nicotine injections in dogs
M. Nakamura, T. Haga, M. Miyano, H. Sasaki and T. Takishima
The dose-response curves of the central and peripheral airways to
intravenously injected nicotine were studied in 55 anesthetized dogs. With
intact vagi, nicotine caused a dose-dependent increase in central airway
resistance (Rc) similar to the increase in peripheral airway resistance
(Rp) at concentrations ranging from 4 to 64 micrograms/kg. However, the
responses of both Rc and Rp fell progressively when sequential doses of
nicotine greater than 256 micrograms/kg were administered. With intact vagi
and the administration of propranolol, there was a greater increase in Rp
than in Rc at a nicotine dose of 64 micrograms/kg (P less than 0.05). With
vagotomy, the responsiveness of both central and peripheral airways to
nicotine decreased with doses of nicotine less than 64 micrograms/kg, but
with doses of nicotine greater than 256 micrograms/kg the suppressive
effect of nicotine on both Rc and Rp was less than that seen with intact
vagi. Under conditions in which the vagi were cut and atropine
administered, the responsiveness of nicotine was even further depressed.
Combinations either of atropine and chlorpheniramine or atropine and
phenoxybenzamine also completely blocked reactions to nicotine.
Additionally reactions to nicotine were completely blocked by
hexamethonium. These results suggest that nicotine increases both Rc and Rp
mainly through a vagal reflex and stimulation of the parasympathetic
ganglia.
