Abstract

Objective: To study the dilatory effects of ketamine on the tracheal muscle against bradykinin induced bronchoconstriction.
Methodology: Guinea pig tracheal chain was first dissected and cut into 2-3mm wide rings and was placed in Krebs Henseleit solution. The muscle activity was recorded by Research Grade Isometric Force Transducer (DT-475, USA) on power lab data acquisition unit. Effect of increasing concentration of acetylcholine (control group) and bradykinin were recorded and semi-log dose response curves were plotted. Response with acetylcholine was considered to be 100 percent. Ketamine was then added in a fixed dose and its effect with increasing doses of bradykinin was recorded and plotted on a cumulative response curve.
Results: Acetylcholine produced maximum tissue contraction with mean±SEM of 0.015±0.0006. Bradykinin produced reversible contraction at maximum mean±SEM of 0.014±0.0007 mV. Ketamine reduced the contraction of the guinea pig tracheal muscle at 300 µM having a mean±SEM value of 0.010±0.0003 mV. A maximum response of 38% was seen with the dose response curve shifting downwards and to the right.
Conclusion: Bradykinin stimulated tracheal muscle was significantly ameliorated by ketamine, indicating that this intravenous general anesthetic can be given in asthmatic individuals or those having airway hyperresponsiveness undergoing intubation or surgery. The underlying mechanism of action of ketamine in these individuals can be linked to the inhibition of bradykinin, which is an important mediator in asthma.

Key words: Acetylcholine, bradykinin, ketamine, tracheal muscle, bronchodilatation.