Light and electron microscopic radioautographic study on the incorporation of 3H-thymidine into the lung by means of a new nebulizer.

The aim of this study was to investigate whether the water particles produced by a nebulizer can reach the alveoli of the lung when they are inhaled with the air. For the purpose of demonstrating water particle incorporation into the lung, light and electron microscopic radioautography with tritiated thymidine was employed. Tritiated thymidine was dissolved in distilled water and nebulized to fine water particles with a new type nebulizer named Shinki, then inhaled by mice. The lungs were taken out and processed by either rapid-freezing and freeze-substitution for dry-mounting radioautography or conventional chemical fixation for wet-mounting radioautography. By wet-mounting radioautography, silver grains were observed in the nuclei of a few alveolar type 2 cells and interstitial cells, demonstrating DNA synthesis. By dry-mounting radioautography numerous silver grains were located diffusely in all the epithelial and interstitial cells, demonstrating diffuse localization of soluble radioisotope-labeled compounds. These results show that water particles produced by the Shinki nebulizer can directly reach the alveoli and thus, better therapeutic effect can be acquired with the Shinki nebulizer than with the usual nebulizer. Further, the nebulizer can be used for the radioautographic studies of the lung in demonstrating incorporation of some drugs into alveolar tissues.