Journal of Applied Physiology, Vol 64, Issue 3 1223-1228, Copyright © 1988 by American Physiological Society
Tracheal narrowing during histamine-induced bronchoconstriction
H. Baier, J. L. Rodriguez, A. Chediak and A. Wanner
Department of Medicine, University of Miami, Mount Sinai Medical Center, Florida 33101.
To determine whether tracheal narrowing accompanies histamine-induced
bronchoconstriction and whether a cholinergic reflex is involved in the
tracheal and bronchial responses, we determined specific pulmonary
resistance between the carina and the pleura (sRL) and tracheal volume
(Vtr) with an indicator-dilution technique in conscious sheep. Immediately
postdelivery of histamine aerosol (7.5 mg histamine base) mean sRL
increased by 223% (P less than 0.05), and mean Vtr decreased by 25% (P less
than 0.05). The duration of the changes was similar, with a return to
base-line values within 60 min. With increasing doses of histamine up to 30
mg, there was a corresponding increase in mean sRL, whereas the maximum
effect on Vtr was already reached after 7.5 mg of histamine. Atropine (0.2
mg/kg iv) increased mean Vtr by 77% (P less than 0.05) and blunted the
histamine effects on sRL, whereas the histamine effects on Vtr were
abolished. Intravenous histamine or carbachol aerosol had similar effects
on sRL and Vtr. We conclude that in conscious sheep 1) histamine produces
both tracheal and bronchial constriction with a similar time course, 2)
there is a base-line vagal tone in the trachea and not the bronchi, 3) the
cholinergic reflex component of histamine-induced constriction is greater
in the trachea than the bronchi, and 4) this difference between the trachea
and bronchi is not due to differential aerosol deposition or cholinergic
responsiveness.
