Effect of heating rate on evaporative heat loss in the microwave-exposed mouse

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Abstract
Male CBA/J mice were adiministered heat loads of 0-28 J .cntdot. g-1 at specific absorption rates (SAR) of either 47 or 93 W .cntdot. kg-1 by exposure to 2450-MHz microwave radiation at an ambient temperature of 30.degree. C while evaporative heat loss (EHL) was continuously monitored with dew-point hygrometry. At an SAR of 47 W .cntdot. kg-1 a threshold heat load of 10.5 J .cntdot. g-1 had to be exceeded before EHL increased. An approximate doubling of SAR to 93 W .cntdot. kg-1 reduced the threshold to 5.2 J .cntdot. g-1. Above threshold the slopes of the regression lines were 1.15 and 0.929 for the low- and high-SAR groups, respectively. The difference in threshold and not slope attributes to the significant increase in EHL when mice are exposed at a high SAR (P < 0.02). In separate experiments a SAR of 47 W .cntdot. kg-1 raised the deep body temperature of anesthetized mice at a rate of 0.026.degree. C .cntdot. s-1, whereas 93 W .cntdot. kg-1 raised temperature at 0.049.degree. C .cntdot. s-1. Hence the sensitivity of the EHL mode of heat dissipation is directly proportional to the rate of heat absorption and to the rate of rise in body temperature. This contradicts the notion that mammals have control over whole-body heat exchange only (i.e., thermoregulation) but instead indicates that the EHL system is highly responsive to the rate of heat absorption (i.e., temperature regulation).

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