Hyperthermic effects on reticuloendothelial system particulate uptake.

Reticuloendothelial system (RES) particulate uptake (PU) of vascular debris influences survival from extreme hyperthermia. Little is known of the effect of extreme hyperthermia, unrelated to fever, on RES PU shortly after reaching a maximum core temperature (T(c)). Relative to normothermic rats (T(c)=38.0 degrees C), rats at T(c)=42.6 degrees C had significantly higher, while T(c)=42.0 degrees C rats had significantly lower total RES tissue (lung, liver, spleen) PU of fluorescent microspheres (1 µ), when compared to rats at T(c)=42.6 or 38.0 degrees C. These findings suggest at T(c)=42.6 degrees C, rats were not actively thermoregulating. As such, more blood remained in the core than in the periphery, which resulted in greater core RES tissue PU. In contrast, to reduce or control core heat, rats at T(c)=42.0 degrees or 38.0 degrees C directed more blood to the periphery, which reduced core RES tissue PU. Blood flow patterns as directed by the state or degree of active thermoregulation is likely an influence of hyperthermia on RES PU.