Influence of prior heat treatment on the effects of heat alone or combined with X-rays on mouse stromal tissue

Histopathological changes in the skin and subcutaneous tissues of mouse legs after treatment with hyperthermia

The right hind legs of mice wee heated in a waterbath at 44 degrees C. The animals were killed at various time intervals after exposure. Tissue damage was studied histologically. After 15 min exposure light and reversible changes were seen including oedema and some neutrophilic inflammatory infiltration immediately after treatment. After 30 min exposure an extensive inflammatory infiltrate and strong oedema were seen during the first days after treatment. Adjacent to areas in the skin with strong oedema extensive muscular necrosis was observed. The muscular tissue regenerated almost completely in three weeks. After 60 min heating the histological picture was dominated by massive necrosis of muscle, subcutaneous fat tissue and skin during the first week after treatment followed by local ulceration. From about the 7th day after treatment regeneration of the epithelium started and granulation tissue could be observed in the margin of the ulceration. Healing of the skin was completed at about day 21 after treatment. Our results indicate that heat induced tissue damage in some tissues is due to a direct effect on the cells composing the tissue (e.g., fat cells in subcutaneous fat) but that, in most other tissues (e.g., muscle and skin) it is a consequence of damage to the vasculature.

Thermotolerance of the spinal cord after fractionated hyperthermia applied to the rat in the cervical region

The effects of heat treatment at 42.9 +/- 0.4 degrees C for 30-90 min of rat cervical spinal cord (cervical 5-thoracic 2) were investigated in animals which had received a priming treatment at 42.3 +/- 0.4 degrees for 60 min in the same region 24 hours before. Hyperthermia to the cervical region in the rat was applied by a coaxial double ring radiator, operating at a frequency of 434 MHz. The test heat treatment led to neurological complications, ranging from unco-ordinated use of the forelegs to paralysis of both forelegs. Death was observed, presumably as a result of respiratory paralysis. The animals that received the priming heat treatment were more resistant to heat injury than those without priming. The LD50, 60 days, for animals without and with priming treatment was respectively at 41 +/- 2 min 42.9 degrees C and at 88 +/- 7 min 42.9 degrees C. The TTR calculated from the LD50, 60 days, data is 2.1 +/- 0.2. Almost all animals, without priming, that did not die as a result of the treatment, recovered in the period from day 1 to day 60 after hyperthermia. Animals that had received a priming exposure were less able to recover from neurological symptoms induced by the test heat treatment. For this reason the induced resistance to thermal injury after priming exposure was more pronounced in the data on lethality than on neurological symptoms. Spinal cord histology from animals that did not recover from neurological symptoms showed extensive non-vascular damage to both gray and white matter.