Stimulation of DNA synthesis in the lungs of hamsters exposed intermittently to nitrogen dioxide

Abstract

Stimulation of [³H]thymidine incorporation in the lungs of hamsters exposed singly and repeatedly to 10 ppm NO₂ was studied. Within 24 hr of the first exposure to NO₂, the response was characterized by a marked increase in [³H]thymidine labeling in the bronchi, bronchioles, and alveolar ducts, but not in the trachea or the peripheral alveoli. If, after the first NO₂ exposure, subsequent exposures were repeated daily, no further stimulation of [³H]thymidine incorporation was observed in any part of the respiratory tract. However, if the interval between the first and subsequent exposures was 2–3 days rather than 1 day, stimulation of [³H]thymidine incorporation was observed in the bronchi, bronchioles, and alveolar ducts for up to 21 NO₂ exposures. A significantly greater increase in [³H]thymidine incorporation was observed when the interval between subsequent exposures was extended to 7 days. However, no repeated exposure, whether at 2–3 or 7 day intervals, was as effective as the first NO₂ exposure in stimulating incorporation of [³H]thymidine.