Probable strain differences of rats in susceptibilities and cardiopulmonary responses to chronic hypoxia.

Susceptibility to chronic hypoxia in the form of simulated high altitude (HA) have been compared in the adult male Hilltop (H) and Madison (M) Sprague-Dawley rats in terms of their metabolic, hematological and cardiopulmonary responses. Following exposure to either 18 000 or 20 000 ft for 30-40 days, 60-70% of the H rats died or became obviously morbid in contrast to a total absence of morbidity or mortality in the M rats. Autopsy of dead and morbid H rats revealed abdominal and pleural effusions. Oxygen consumption remained normal in both H and M rats. Hematocrits were slightly higher in the H rats than in the M rats. The lungs of both strains were hypertrophied but they showed no evidence of edema or gross lesions. The peak right ventricular pressures of the H and M strains were 73.6 +/- 7.4 and 49.5 +/- 6.5 mm Hg (mean +/- SD), respectively. The percent increase in total ventricular, right and left ventricular weights per 100 g body weights in the H rats were 80, 300 and 30, respectively, as compared to 20, 200 and 0 in the M rats. These changes suggest that the greater susceptibility to chronic HA exposure observed in the H rats is related to a more severe right ventricular overloading and perhaps failure, secondary to a more extreme pulmonary hypertension.