Effect of chloroquine on the stability of rat kidney lysosomes in vivo and in vitro.

1. Chronic administration of chloroquine to rats results in increased urinary excretion of lysosomal acid phosphatase, muramidase and cathepsin D. 2. Various concentrations of chloroquine caused lysosomal membrane swelling as shown by decrease of light absorbance in lysosomal suspensions. 3. Incubating lysosomal suspensions in the presence of chloroquine resulted in a marked lysosomal acid phosphatase release. 4. Addition of acetylsalicylic acid, a lysosomal membrane stabilizer, into a lysosomal suspension containing chloroquine, reduced the degree of lysosomal membrane swelling and acid phosphatase release. 5. The results suggest a labilizing effect of chloroquine on rat kidney lysosomes.