Effect of altitude exposure on induction of streptococcal endocarditis in young and middle-aged rats.

Young (age 2 months) and middle-aged (age 10 month) rats were injected once with a culture of Streptococcus sanguis and exposed for 24 h to 7620 m altitude. At 6 d 54% of the exposed and 30% of the unexposed middle-aged rats had bacterial endocarditis. Myocarditis developed in 63% of the injected exposed rats of both ages, in 11% of the injected unexposed middle-aged rats, and in none of the unexposed young adults. Interstitial nephritis was found in 46-66% of the injected, unexposed young and middle-aged rats and in 70-86% of the injected, exposed young and middle-aged rats, respectively. About 95% of all injected rats survived 6 d. No evidence of hemoconcentration was found. The increase in cardiac disease induced by altitude was probably due to deleterious effects of hypoxia on the myocardium, and cellular defenses, and to physiological and possible immunological changes associated with aging.