Influence of macrophages on microdistribution of inhaled UO2 aerosol in rat lung

Following the inhalation of an aerosol of UO2 (mass median aerodynamic diameter = 3 microns and geometric standard deviation = 1.6) the lungs of male albino rats were populated by foci containing UO2 particles. A method of neutron-induced autoradiography on Lexan plastic was used to reveal these foci in thin sections cut from the lung. For masses of UO2 in the lung that differed by more than a factor of 10 (39 to 450 micrograms) the number of foci per g of lung increased, but not in proportion to the mass of UO2 deposited. This limited increase in the number of foci was considered to result from physiological limitations on the number of alveolar macrophages available for engulfing the UO2 particles.