Quinacrine-blocked desensitization of adrenoceptors after immobilization stress or repeated injection of isoproterenol in rats.

Repeated forced immobilization or repeated administration of isoproterenol reduces the number of beta adrenoceptors in the heart and spleen of rats. Isoproterenol, but not immobilization, reduced the number of beta receptors in the lung. These changes in beta adrenoceptors were prevented by administration of quinacrine, a phospholipase A2 inhibitor, although the drug had no effect on beta adrenoceptors when given alone. Immobilization, but not isoproterenol, reduced the number of alpha-1 adrenoceptors in the heart but had no effect on the lung. Quinacrine treatment decreased the number of alpha-1 receptors in heart and lung but increased alpha-2 receptors in the spleen. The changes in receptor number attending exposure to agonists are usually consistent with the expected changes. The effects of quinacrine on such changes suggest that phospholipids are involved in modulating the changes in number of receptors or their availability to interact with ligands.