Differential Response of the Permeability of the Rat Liver Canalicular Membrane to Sucrose and Mannitol Following in Vivo Acute Single and Multiple Exposures to Microwave Radiation (2.45 GHz) and Radiant-Energy Thermal Stress

Both acute and chronic exposures to microwave radiation altered the function of the rat canalicular membrane. A single acute exposure to microwave radiation [$80\ {\rm mW}/{\rm cm}^{2}$, 2.45 GHz, continuous wave, 30 min exposure (SAR ≅ 72 W/kg)] or a matched radiant-energy thermal load, both designed to raise core body temperature approximately 3°C, decreased the permeability of the canalicular membrane of male Sprague-Dawley rats to sucrose. The change in canalicular membrane permeability was demonstrated by a significant increase in the percentage of$[{}^{3}{\rm H}]\text{sucrose}$ recovered in bile following its administration by a segmented retrograde intrabiliary injection. Similar acute exposures to microwave and radiant-energy thermal sources produced no significant alterations in canalicular membrane permeability to$[{}^{14}{\rm C}]\text{mannitol}$. In both acute exposure protocols, a rapidly reversible increase in bile flow rate was observed. Four exposures (30 min/day × 4 days) to either microwave radiation$(80\ {\rm mW}/{\rm cm}^{2})$ or a matched radiant-energy thermal load resulted in a significant depression in bile flow rate at normothermic temperatures. Animals receiving multiple exposures to microwave radiation had significant decreases in canalicular membrane permeability to both$[{}^{3}{\rm H}]\text{sucrose}$ and$[{}^{14}{\rm C}]\text{mannitol}$, while similar exposure to radiant-energy thermal load alone altered canalicular membrane permeability to$[{}^{3}{\rm H}]\text{sucrose}$. An examination of the hepatic clearance of sucrose and mannitol following acute microwave exposure demonstrated no significant differences. Thus acute single exposure to microwave and radiant-energy thermal loads produced similar alterations in canalicular membrane permeability. Conversely, multiple exposures produced nonreversible changes in bile flow rate and canalicular membrane permeability, with microwave exposure producing greater alterations in the function of the canalicular membrane than an equivalent radiant-energy thermal load.