Regional differences in apoptosis in murine gliosarcoma (T9) induced by mild hyperthermia.

There are several reports of apoptosis induced by mild hyperthermia both in vitro and in vivo. However, in tumour nodules, regional differences in apoptosis induced by hyperthermia have not been studied morphologically or quantified. In this study, apoptosis was identified on the basis of its characteristic morphology, and was quantified in different tumour regions (margin and centre) by light and electron microscopy and discussed the correlation with necrosis. Apoptosis was induced in solid nodules of gliosarcoma (T9) in vivo by heating for 30 min in a water bath at 43°C. The gliosarcoma cells showed a rapid increase in the number of apoptotic cells following mild hyperthermia. There was a regional difference in the rate of apoptosis immediately after hyperthermia. Necrosis was markedly enhanced only in the centre of the tumour 3 and 6 h after hyperthermia. These combined responses of apoptosis and necrosis seem to be caused by the microenvironmental change in the intratumour location.