Asthma-drugs influence smooth muscle in both bronchi and lung vessels. Some vasodilation may be expected with isoprenaline and theophylline, whereas selective beta 2-stimulants seem to be without vascular effect. Isoprenaline relaxed to some extent 14 of 20 pulmonary artery strips after maximum contraction with carbacholine, acetylcholine and prostaglandin F2 alpha (Fig. 1b). Total reversibility occurred in only one specimen, the average relaxation of all specimens tested was 22 +/- 6%. 2. Eight of 10 specimens contracted with histamine, prostaglandin F2 alpha or serotonin were relaxed by theophylline (Fig. 1b), average relaxation was 37 +/- 25%. No statistically significant difference existed between relaxation induced with isoprenaline or theophylline.
