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Spasmolytic drugs possessing a musculotropic action appear to be the most effective in inhibiting the motility of the human myometrium in vitro. Substances whose action is mediated via a predominently β-receptor mechanism have relatively little or no effect on this preparation.

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.