A comparison of drug-induced responses on rat tracheal, bronchial and lung strip in vitro preparations.

1. A preparation of rat trachea and a new preparation of rat bronchi are described. Both preparations are fluid-filled and the intraluminal pressure is monitored. 2. A preparation of rat peripheral airways, the lung strip, is described. The preparation consists of a thin strip of lung parenchyma which is superfused, and contractions monitored isotonically. 3. The rat trachea and bronchi have no intrinsic tone but increases in pressure are elicited in response to methacholine. The preparations relax in response to isoprenaline and aminophylline in the presence of a methacholine-induced contraction. Both preparations respond weakly and show tachyphylaxis to 5-hydroxytryptamine (5HT). 4. The lung strip contracts with equal magnitude to methacholine and 5-HT. It exhibits intrinsic tone which is inhibited by indomethacin and relaxed by isoprenaline.