Augmentation of alpha-adrenergic contractions in the trachealis muscle of living dogs.
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.
D000818:Animals; D004285:Dogs; D004558:Electric Stimulation; D005260:Female; D006632:Histamine / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D010277:Parasympathomimetics / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000502:physiology; D013566:Sympathomimetics / Q000502:physiology*; D014132:Trachea / Q000187:drug effects*
D010277:Parasympathomimetics; D013566:Sympathomimetics; D012701:Serotonin; D006632:Histamine; D009638:Norepinephrine; D010646:Phentolamine