Abstract

When added to incubations in vitro. (+/-)-propranolol, a cationic amphiphilic drug, causes profound alterations in incorporation of [32P] orthosphosphate into rat cerebral cortex phospholipids. These include increases in the labeling of phosphatidic acid and polyphosphoinositides abd a decrease in the labeling of phosphatidylcholine. Similar changes occurred in a dose-dependent manner in incubations of cerebral cortex mince, prepared from animals injected i.p. 30 min before death with doses of propranolol ranging from 7.5 to 45 mg/kg. All changes in total incorporation and in labeling pattern had disappeared 3 hr after injection, indicating the reversibility of the effect. Repeated injections of low doses of propranolol (7.5 mg/kg) brought about significant changes in the labeling of brain cortex mince phospholipids, and especially a reduction in total incorporation. Addition of propranolol to kidney and liver minces caused reductions in the labeling of phosphatidylcholine and phosphatidylethanolamine and selective increases in the labeling of acidic lipids, restricted to phosphatidic acid in liver and phosphatidylinositol in kidney. After injection of 45 mg of propranolol per kg, but not at 15 mg/kg, some alterations in the labeling pattern were observed in liver and kidney minces. The differential response of tissues to propranolol injections can be explained on the basis of the pharmacokinetics of drug distribution and clearance and metabolic capacities of the tissues. Changes in phospholipid metabolism may be in part responsible for deleterious side effects that can occur during therapy with high doses of propranolol.