title: Cardiac activity during airway resistance alterations with intravenous and inhaled methacholine.
abstract: Measurement of airway contractile responses to methacholine (MCh) is an important investigational tool in humans and mice. However, i.v. administration of MCh in murine models may suffer from potential cardiac sequelae produced by stimulation of cholinergic receptors within cardiac muscle. Therefore, we studied the i.v. (0-10,000 microg/kg) and aerosolized (inhaled; 0-25 mg/ml) administration of MCh, to determine their effects on pulmonary resistance (RL) and cardiac muscle activity (as heart rate; HR) in anesthetized, mechanically-ventilated C57Bl6 mice. MCh, i.v., increased RL but produced: (1) prolonged asystole (29-47 sec); (2) subsequent overshoot of baseline HR; and (3) prolonged HR recovery times (7-25 min), suggestive of sympathetic modulation after cholinergic stimulation. In contrast, inhaled MCh aerosol produced no change in HR, while increasing RL similar to i.v. MCh. These results suggest that, for specific instances utilizing the plethysmographic technique, inhaled MCh aerosol may be superior to i.v. administration, due to the avoidance of potential bouts of asystole that can confound experimental results and lead to premature death of mice.
authors.affiliation: Asthma, Allergy, and Airway Research Center, Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh School of Medicine, 628NW Montefiore University Hospital, Pittsburgh, PA 15213, USA. ameredesbt@msx.upmc.edu
authors.forename: Bill T
authors.initials: BT
authors.lastname: Ameredes
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000280:Administration, Inhalation; D000403:Airway Resistance / Q000187:drug effects*; D000704:Analysis of Variance; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D016084:Bronchoconstriction / Q000187:drug effects*; D016085:Bronchoconstrictor Agents / Q000008:administration & dosage* / Q000494:pharmacology; D001993:Bronchodilator Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004333:Drug Administration Routes; D004347:Drug Interactions; D004562:Electrocardiography / Q000379:methods; D006323:Heart Arrest / Q000139:chemically induced; D006339:Heart Rate / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007275:Injections, Intravenous; D008297:Male; D016210:Methacholine Chloride / Q000008:administration & dosage* / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D011930:Reaction Time / Q000187:drug effects; D013997:Time Factors
chemical_list: D016085:Bronchoconstrictor Agents; D001993:Bronchodilator Agents; D016210:Methacholine Chloride; D001285:Atropine; D000109:Acetylcholine