A method for recording smooth muscle and vascular responses of the blood-perfused dog trachea in situ.

1 A method is described for measuring responses of dog tracheal musculature and vasculature in situ. 2 The upper two thirds of the trachea was perfused with blood through both cranial thyroid arteries at a constant pressure. The blood flow through the arteries was measured with an electromagnetic flowmeter. The response of the tracheal musculature was measured as a change in pressure in a water-filled cuff inserted into the trachea via the mouth. Drugs were injected close-arterially. 3 Acetylcholine produced dose-dependent increases in blood flow rate (vasodilatation) and in tracheal intraluminal pressure (tracheal constriction). These responses were antagonized by atropine. 4 Isoprenaline produced vasodilatation which was blocked by propranolol. Adrenaline and noradrenaline caused vasocontriction which was blocked by phentolamine. 5 All three catecholamines produced a decrease in tracheal intraluminal pressure (tracheal dilatation). The tracheal dilatation in response to adrenaline and noradrenaline was converted to constriction by propranolol. The tracheal constriction thus unmasked was abolished specifically by phentolamine. 6 From these results it is concluded that the tracheal musculature and vasculature contain muscarinic receptors, and excitatory alpha- and inhibitory beta-adrenoceptors. In the tracheal musculature beta-adrenoceptors predominate over alpha-adrenoceptors; the reverse is true in the tracheal vasculature.