Journal of Applied Physiology, Vol 54, Issue 6 1558-1566, Copyright © 1983 by American Physiological Society
Augmentation of alpha-adrenergic contractions in the trachealis muscle of living dogs
J. K. Brown, R. Shields, C. Jones and W. M. Gold
Discrepancies exist between reported effects of histamine on the
alpha-adrenergic responsiveness of the canine trachealis muscle. Therefore,
using an in situ preparation described recently (J. Appl. Physiol.:
Respirat. Environ. Exercise Physiol. 49: 84-94, 1980), we tested the
effects of histamine and other agents on alpha-adrenergic responses in the
trachealis muscle of 34 anesthetized dogs. Under basal conditions, maximum
alpha-adrenergic responses were small [3 +/- 1 (SE) g/cm] compared with
those induced by a supramaximal parasympathetic stimulus (45 +/- 3 g/cm).
After exposure of the muscle to histamine, responsiveness increased
markedly to alpha-adrenergic stimuli, which included tracheal arterial
injections of norepinephrine and phenylephrine or electrical stimulation of
sympathetic nerves. Augmented alpha-adrenergic responsiveness persisted for
20 min after the end of contractions induced by histamine. Serotonin and
long-acting, but not short-acting, cholinergic agonists also potentiated
alpha-adrenergic responsiveness. We concluded that exposure of the
trachealis muscle in living dogs to a variety of constrictor stimuli
potently augmented its alpha-adrenergic responsiveness.
