We evaluated cardiovascular effects and effectiveness of
isoetharine,
metaproterenol and
salbutamol, when administered intratracheally to relieve
methacholine-induced
bronchospasm in dogs anaesthetized with 50 per cent
nitrous oxide,
oxygen,
halothane and mechanically ventilated.
Methacholine 2 micrograms X kg-1 X hour-1 was administrated first followed by
halothane (1 MAC) for 30 minutes (control), then
metaproterenol,
isoetharine or
salbutamol.
Metaproterenol (15 mg) significantly decreased transpulmonary pressure to 20.1 +/- 0.5 (SE) from 22.5 +/- 1.15 cmH2O (p less than 0.025) after three min and to 15 +/- 0.5 cmH2O (p less than 0.005) after 90 min.
Isoetharine (2.5 mg) decreased transpulmonary pressure after five min to 22.1 +/- 1 from 24.5 +/- 1.5 cmH2O (p less than 0.05), and to 21.75 +/- 0.55 mmH2O after 90 min.
Salbutamol 25 micrograms X kg-1 decreased transpulmonary pressure to 20.7 +/- 0.75 from 24.25 +/- 1.28 after three min and to 16 +/- .5 after 90 min. The peak effects on airway pressure occurred at 15 min for
metaproterenol, 25 min for
salbutamol and 20 min for
isoetharine. Pulmonary vascular resistance was not significantly changed during
halothane anaesthesia alone but decreased significantly after
metaproterenol and
isoetharine infusion. Heart rate increased ten per cent after
metaproterenol, three per cent after
isoetharine, and five per cent after
salbutamol. No arrhythmias occurred in any group. Cardiac output increased significantly to 3.25 +/- 0.2 from 1.5 +/- 0.17 L X min-1 (p less than 0.025) after
metaproterenol to 3.2 +/- .025 from 1.45 +/- .009 after
salbutamol and was unchanged after
isoetharine.
Metaproterenol and
salbutamol in the presence of 1 MAC
halothane anaesthesia relieved
methacholine-induced
bronchospasm more rapidly than did
isoetharine. The onset of effect was 3 +/- 0.05 min for
metaproterenol and
salbutamol and 5 +/- 0.01 min for
isoetharine. The effect lasted 210 +/- 10.5 min for
metaproterenol, 170 +/- 12.5 min for
salbutamol and 90 +/- 4.75 min for
isoetharine.