Effect of hyperthermia on normal and neoplastic cells in vitro.

for periods of 15 to 60 min resulted in disappearance of nucleolar DNA and diffusion of nucleolinar material, as demonstrated by toluidine blue-molybdate, acid phosphatase, and lead staining throughout the nucleolus. Ultrastructural studies of the heated cells indicated that the fibrillar component of the nucleolus, like the nucleolini, became diffusely distributed throughout the nucleolus and that the granular component of the nucleolus almost completely disappeared. Hyperthermia led to the forma tion of cytoplasmic inclusions in 100% of cells with nucle oli. The inclusions were cytochemically similar to the body of the nucleolus observed by light microscopy and consisted of aggregations of ribosome-like granules in electron micrographs. Evidence is presented to indicate that the inclusions were derived from the nucleolus and possibly from the granular component. Hyperthermia also resulted in disaggregation of polysomes. The effects of heating to 46°for 15 min were completely reversible.