The effect of terbutaline upon myosin preparations of the human uterus.

It has been perceived that the phosphate (P) content of the human uterus myosin was considerably lower (half or less) in patients treated with terbutaline before delivery than that of untreated patients. Therefore the in vitro effect of terbutaline was investigated upon uterine myosin. The results showed that the presence of terbutaline in the incubation medium without ATP decreased the performed (endogenous) P content of myosin slightly, whereas in the presence of ATP terbutaline facilitated release of the phosphoryl groups from myosin parallel with the increase of terbutaline concentration. Although at low concentrations of terbutaline (in the micromolar range) a few phosphoryl groups are still incorporated in myosin, the time reaching the maximum of P incorporation was prolonged.