EFFECTS OF EXERCISE ON PARTICLE DEPOSITION IN SYRIAN GOLDEN-HAMSTERS

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Abstract
Since the biologic effects of inhaled toxic particles depend on the amount of particles deposited in the respiratory system, effects of exercise and its associated increase in ventilation on the deposition of inhaled particles were investigated. Total retention and patterns of distribution of a 99mTc sulfur colloid aerosol (activity median aerodynamic diameter, 0.38 .mu.m; geometric SD, 1.35) were measured in male Syrian golden hamsters. Animals were either anesthetized, resting or exercising on a treadmill during a 15-min aerosol exposure. Each hamster''s O2 consumption (.ovrhdot.VO2) was continuously monitored during the exposure; immediately after, the animal was killed. Lungs were excised, inflated and dried in a microwave oven. The rigid lungs were sliced and dissected in a predetermined way so that retention at specific locations could be compared. Radioactivity and weight of 40 pieces from each of 12 hamsters were measured. Uniformity of deposition was described by an evenness index (EI) for each piece, EI = (cpm/g)piece/(cpm/g) whole lung. With theoretical uniformity of retention, all EI values should be 1.0. During aerosol exposure, the exercising group had a .ovrhdot.VO2 of 5.0 .+-. 0.6 (SD) ml STPD[standard temperature and pressure, dry]/min per 100 g, which was 2 times the resting group (2.5 .+-. 0.4) and 4 times the anesthetized group (1.2 .+-. 0.2). The total retention of particles in the lungs increased in a parabolic manner as a function of .ovrhdot.VO2; the exercising animals had a retention 6 times greater than the anesthetized animals. The increased retention in running hamsters may reflect increased ventilation alone or increased collection efficiency. Each animal''s activity level also affected local distribution of particles in the lung. Resting hamsters had a significant gradient in particle distribution with more radioactivity per gram in the apex and less in the base. In exercising animals, the magnitude of the apex-base gradient did not change. Anesthesia increased the variability of EI values and abolished the apex-base gradient. Increased deposition produced by exercise may influence the toxicity of harmful particles in the lung.