The effect of isoprenaline on the contraction of smooth muscle produced by histamine, acetylcholine or other agents

Isoprenaline given intravenously is a more potent antagonist of bronchospasm produced by histamine than of that produced by acetylcholine in the anaesthetised guinea-pig. This greater activity of isoprenaline against histamine was also observed on isolated tracheal muscle and ileum of the guinea-pig. It was also found in isolated guinea-pig ileum that stimulation of the periarterial sympathetic nerves produced a greater inhibition of contractions produced by histamine or 5-hydroxy-tryptamine than of those produced by acetylcholine or bradykinin. The inhibitory actions of isoprenaline were absent in tissues without β-receptors and tissues in which the β-receptors were blocked by pronethalol.