Mechanism of the inhibitory action of indomethacin on smooth muscle.

1. Strips of muscle from the wall of the guinea-pig stomach contracted in response to electrical field stimulation (100 ms pulses, 0.2 Hz) or to histamine (1 mug/ml), and these responses were inhibited by indomethacin (2-20 mg/100 ml).2. Glycerol-extracted strips of stomach muscle developed tension when exposed to a mixture of ATP, CP, magnesium chloride and calcium chloride. The tension response was not altered by indomethacin (50 mg/100 ml).3. Indomethacin failed to alter the content of ATP or of CP in strips of stomach muscle.4. The calcium content of strips of stomach muscle increased in response to 30 min of electrical stimulation (100 ms pulses, 0.2 Hz). The uptake of calcium and the contraction of the strips were inhibited by indomethacin (2-20 mg/100 ml) to a similar extent.5. Calcium uptake by electrically stimulated guinea-pig aorta was inhibited by lower concentrations of indomethacin than were required by stomach muscle.