Long-term study of the distribution of soluble chromate-51 in the rat after a single intratracheal administration.

Soluble chromate-51 (as sodium dichromate dihydrate) was applied intratracheally in rats, after which distribution of radioactivity was followed for 40 d by autoradiograph and gamma scintillation counting. Doses were 0.01 and 0.25 mg/kg in physiological saline solution. After administration of a 0.25-mg/kg dose, lung radioactivity declined rapidly for 2 to 3 d, at which time about a third of the total dose remained in the lung. The radioactivity in the lung was localized mainly intracellularly in the parenchyma. Microautoradiography indicated that the 51Cr was localized mostly in the type II alveolar cells. At the end of the experiment (40 d after administration), approximately 10% of the applied dose was found in the lung. The highest 51Cr quantities and concentrations were determined in the lung throughout. In the blood serum, the decline of radioactivity concentration was characterized by an apparent half-life of 3 to 4 d for the period from 2 to 15 d. The concentration time courses for the other tissues and organs indicated longer apparent half-lives, ranging from 14 to 50 d. Kidney, erythrocytes, and testis maintained their Cr levels for a period of 10 to 15 d, after which the decrease of concentration became evident. The results obtained at the lower dose level of 0.01 mg/kg were largely dose-proportional to those obtained at the higher dose level of 0.25 mg/kg.