Morphological changes during acute experimental short-term hyperthermia.

Wistar rats have been exposed to progressively higher temperatures for 30 minutes to 40.5 degrees Celsius. The animals were sacrificed 30 minutes after cessation of exposure. Harvested organs (heart, lung, liver, pancreas, kidneys, and adrenal gland) show numerous vascular lesions. Massive red blood cells extravasation and vascular stasis partially fragments the myocardial fibers. Pulmonary capillary dilatation and red blood cells intra-alveolar extravasation cause a hemorrhagic alveolitis that tends to a red hepatization. The liver responds by dilating centrolobular veins, vessels in port area and by granulo-vacuolar dystrophy. Pancreas seems less affected. Vascular hyperemia is discrete while in kidney the vascular spaces are narrowed and the proximal and distal tubules cloudy intumescent appears. In suprarenal gland appear many interstitial capillary dilatation and blood cells extravasation among cell nests of medulla. All these changes induce functional organ failure.