An isometric method to study respiratory smooth muscle responses in mice

An isometric method to measure the smooth muscle tone of murine tracheas in vitro was developed. Nine trachea rings from just beneath the larynx were prepared free of excess tissue with the help of a binocular microscope. These trachea parts were slipped onto supports in an organ bath containing Krebs' solution. Isometric tension was measured with a force displacement transducer connected to the upper-trachea support, and is expressed as changes in grams force.

The cholinergic agonist carbachol contracted isolated tracheas. Serotonin also induced contractions, but was less potent than carbachol. Histamine induced tracheal contractions only at very high concentrations.

Sympathomimetic β adrenergic agonists relaxed carbachol-precontracted tracheas with the following order of potency: isoprenaline (β₁ and β₂ adrenoceptor agonist) > salbutamol (β₂ adrenoceptor agonist) > prenalterol (β₁ adrenoceptor agonist). Adrenaline and noradrenaline relaxed carbachol-precontracted tracheas, with adrenaline being the more potent relaxant.

For the study of airway reactivity, this mouse trachea model has several advantages over immunopharmacologic models: The immune system of the mouse has been characterized extensively, and many reagents are available to study the immune system and, thus, possible interactions of this system with pharmacological mechanisms. Other animal models used in pharmacology are generally less well defined immunologically.