Differences in the response of the microcirculation to hyperthermia in five different tumours

The response of the microcirculation in five different tumours, growing in 'sandwich' observation chambers in the back of the rat, to hyperthermia was investigated. The tumours investigated encompassed three human xenografted tumours, of which two were carcinomata of the colon and one of the lung, and two isologous rat tumours, the Rhabdomyosarcoma BA1112 and a rat mammary carcinoma. It was concluded (1) that the various tumours required significantly different exposure times for inducing 50% stoppage of the tumour microcirculation (ST50). This seems to indicate that differences in the characteristics of the tumour cells are more important for causing microcirculatory stoppage than is the sensitivity of the cells of the blood vessels. (2) An increase in surface (i.e. volume) was observed in all four tumours examined for this phenomenon. The rate of increase (usually 1-2% per hour at 42.5 degrees C) was, however, significantly different between the various tumours. This rate was higher exposure temperatures (43 and 43.5 degrees C), but this was only investigated for the Rhabdomyosarcoma BA1112. Extensive statistical analysis of this phenomenon of volume increase could not demonstrate a correlation with any of the circulation parameters. (3) The relative velocity of the erythrocytes in selected capillaries in the tumours decreases as a result of the hyperthermic treatment, and is probably related to the tumour-specific ST50. (4) A human colon carcinoma xenograft, one of the tumours investigated, showed strong fluctuations in the parameter 'erythrocyte velocity'. The appearance of such fluctuations did not seem to influence the heat-induced stoppage of the circulation. Probably the phenomenon of fluctuations in the velocities of the erythrocytes in the tumour capillaries is a tumour-specific phenomenon.