Two qualitatively different effects of hyperthermia on acid phosphatase staining in mouse spleen, dependent on the severity of the treatment.

Heating the lower body of the mouse for up to 1.5 hours at temperatures above 41.0 degrees C causes an increase in splenic lysosomal acid phosphatase activity. For mouse temperatures up to 42.3 degrees C the change is probably due to enzyme activation, which reaches a maximum 1.5 hours after heating and then decays in a way which may be related to the transient ability of moderate hyperthermia to potentiate X-ray damage. At temperatures above about 42.5 degrees C hyperthermia results in a qualitatively different lysomal response, probably due to an increased lysosomal membrane permeability. The change is observed immediately after heating and remains high for at least 4 hours. The resultant release of hydrolases into the cytoplasm may be involved in the irreversible cell damage caused by severe hyperthermia.