Effect of repeat irradiation on the tracheal ciliary cell activity.

Rabbit tracheas were initially irradiated with 10 Gy in vitro. A second irradiation of 10 Gy was administered 2 hours later. The initial exposure caused a 25 per cent increase of the ciliary beat frequency during the irradiation--a response which was not found during the second irradiation. Between the exposures, the beat frequency dropped to 20 per cent below the reference level, followed by an 11 per cent overshooting before the second irradiation. Tracheas placed untreated in the experimental chamber for 2 hours and subsequently irradiated with 10 Gy showed a similar pattern of ciliary activity as induced by the initial radiation exposure in the first experiment. The storage during 2 hours did thus not affect the condition of the ciliae. The absence of a great increase of the beat frequency during a second irradiation period may be explained by damages caused by the initial exposure, morphologically seen first a few days later.