Changes in the phospholipid content in the left heart ventricle of male mice during repeated administration of isoprenaline.

1. Male mice were injected 5 mg/kg isoprenaline (IPRO) daily and the heart weight, dry weight and phospholipid content in the left ventricle determined 24 hr after the last injection on days 1, 3, 5 and 10. 2. The phospholipid content sinks during the experiment, but the onset of the change is different in different phospholipids: for diphosphatidylglycerol it is clearly significant after 3 days, for phosphatidylcholine and phosphatidylethanolamine after 5 days and for sphingomyelin after 10 days; the relative amplitude of the change in this latter phospholipid was greatest of all. 3. If IPRO is given for 3 days and physiological saline for next 7 days, the content of some phospholipids (PE, SM and PG) continued to decrease. This suggests an important delayed effect of IPRO action.