Ionic changes evoked by isoprenaline in rat hearts in vivo and in vitro and their reduction by creatinol O-phosphate.

The action of large doses of catecholamines on the Ca and Mg content of rat heart has been examined both in vivo and in vitro. It was observed that the ionic changes evoked in vitro by isoprenaline 10(-5) mol/l were similar to those evoked in vivo by isoprenaline 30 mg/kg and that both were reduced by N-methyl-N-(beta-hydroxy-ethyl)guanidine O-phosphate (creatinol O-phosphate) in a dose-dependent manner. ED50 was equal to 3 x 10(-7) mol/l. These results indicate that the cardionecrotic action evoked in vivo by isoprenaline and its reduction by creatinol O-phosphate may be attributed to a direct action on the myocardial cell.