[Measurement of isometric tracheal tension induced by injection into tracheal arterial circulation in vivo].

In order to evaluate isometric tension in segments of tracheal smooth muscle in vivo, we first investigated the anatomical distribution of arteries supplying the tracheal smooth muscle in 52 dogs. The patterns of the cranial thyroid arteries were classified into the following four types. A) Common type: the cranial thyroid artery leaves the muscular branch, and then divides into the thyroid branch and the tracheal branch. B) The cranial thyroid artery leaves the tracheal branch, and then divides into the muscular branch and the thyroid branch. C) The cranial thyroid artery divides into the muscular branch, the thyroid branch, and the tracheal branch. D) The cranial thyroid artery divides into the tracheal branch and thyroid branch, and lacks a muscular branch. Out of 52 dogs, 62% had common type bilaterally, and 23% had common type unilaterally. All dogs had a tracheal branch. We demonstrated tracheal smooth muscle contraction by intra-arterial administration of acetylcholine, histamine, 5-hydroxy-tryptamine, phenylephrine, and clonidine using isometric technique in vivo. These results suggest that tracheal contraction induced by sympathetic amines is mediated through two subtypes of receptors, alpha 1 and alpha 2, in tracheal smooth muscle.