AbstractThe stability of lysosomes from liver and muscle of adrenalectomized, young rats has been tested by measuring the release of acid hydrolases (RNase, cathepsin D, β‐glucuronidase and aryl sulphatase) from lysosomes under various conditions. Adrenalectomy increased the proportion of enzyme released from the lysosomal particles, as measured in tissue homogenates or fractions. The release, which may have occurred in vivo or during homogenization, probably reflects an increased lysosomal fragility. In muscle (but not in liver) an increase in the total activtiy of acid hydrolases could also be observed after adrenalectomy. The effects of adrenalectomy could not be corrected by saline treatment, and were not due to reduced food intake. All parameters were restored to normal by administration of 300 μg of corticosterone daily for 5 days, and higher doses (3 mg per day) led to further reduction in enzyme release. The stability of muscle and liver lysosomes in vitro was tested by exposing particles to osmotic stress, vitamin A alcohol and acid medium (pH 5). Liver and muscle lysosomes from adrenalectomized rats were less stable when exposed to osmotic stress or vitamin A, but hepatic lysosome were more stable towards acid incubation than particles prepared from normal rats. Differential centrifugation of liver homogenates indicated that more acid hydrolases were associated with the heavier fractions in homogenates from operated animals. An increased particle size in tissues from the adrenalectomized animals may possibly account for the observed changes in lysosomal stability.