Strain Differences in the Response of Inbred Syrian Hamsters to Cigarette Smoke Inhalation2

Male hamsters, 102 from each of 2 inbred hamster lines, were exposed to cigarette smoke twice a day, 5 days/week for up to 100 weeks, in a modified Walton reverse-smoking machine. Sixty sham-smoked and 60 cage-held controls were used for each strain. Smoke exposure for up to 100 weeks had no effect on mortality in either strain, but reduced body weight. Carboxyhemoglobin levels increased markedly immediately after each smoke exposure but returned to baseline levels in less than 24 hours. Serum triglyceride levels and virus profiles of smoke-exposed animals were unchanged. Chronic smoke exposure increased relative weight of the lungs and heart in both strains, but to different degrees. Over 90% of the smoke-exposed animals of both strains showed hyperplastic or neoplastic changes in the larynx. However, microinvasive cancer was nearly 5 times more frequent in 1 strain than in the other. In the inbred line more susceptible to laryngeal hyperplasia, 2 animals developed nasopharyngeal tumors, one of which was malignant. Smoke exposure induced rare benign squamous papillomas in the air passages of both strains. The strain less susceptible to laryngeal hyperplasia exhibited more pulmonary adenomatosis, but its incidence was not significantly affected by smoke exposure. Clumping of pulmonary macrophages was proof that smoke had reached the lungs; 1 strain was more susceptible to this phenomenon than the other. In neither strain did smoke exposure affect the incidence of tumors arising outside the respiratory tract or the degenerative changes characteristic of aging hamsters.