In lightly anesthetized adult sheep, we determined tracheal mucosal blood flow (Q̇tr) by measuring the steady-state uptake of dimethyl ether from a tracheal chamber created by an endotracheal tube provided with two cuffs. Q̇tr normalized for carotid arterial pressure [Q̇tr(n)] was determined before and after the exposure of the tracheal mucosa to aerosolized phenylephrine (0.25-2.0 mg), isoproterenol (0.05-0.8 mg), and metacholine (2.5-20 mg). The same doses of metacholine were also administered during the intravenous infusion of vasopressin. The measurements were repeated after intravenous pretreatment with the respective antagonists phentolamine, propranolol, and atropine. Mean ± SE base-line Q̇tr(n) was 1.2 ± 0.1 ml · min-1 · mmHg-1 · 102. The autonomic antagonists had no effect on mean Q̇tr(n). Phenylephrine produced a dose-dependent decrease in mean Q̇tr(n) (-70% at the highest dose), which was blunted by phentolamine, and isoproterenol produced a dose-dependent increase in mean Q̇tr(n) (40% at the highest dose), which was blocked by propranolol. Metacholine failed to alter mean Q̇tr(n) even when Q̇tr was first decreased by vasopressin. We conclude that in lightly anesthetized adult sheep 1) base-line Q̇tr(n) is not under adrenergic or cholinergic control, 2) a locally administered α-adrenergic agonist decreases and β-adrenergic agonist increases Q̇tr(n) via specific receptor activation, and 3) a locally administered cholinergic muscarinic agonist has no effect on Q̇tr(n).
ASJC Scopus subject areas
- Physiology (medical)