Coronary blood flow in rats native to simulated high altitude and in rats exposed to it later in life

Summary In rats exposed to a simulated high altitude of 3500 m for their whole prenatal and postnatal life a severe cardiac hypertrophy develops. In rats born and first staying 5 weeks at sea level and then being exposed to simulated high altitude, only a unilateral right cardiac hypertrophy occurs. In both groups nutritional coronary blood flow was estimated in left ventricle, right ventricle, and septum and was compared with control animals of similar age. Coronary blood flow was measured at hypoxia in all groups. At first cardiac output was determined by the Fick principle, then⁸⁶Rb was applied and the animals were killed after 55 sec. Activity of⁸⁶Rb was measured in both cardiac ventricles and septum and the fractional uptake was calculated. According to Sapirstein (1956, 1958) the distribution of⁸⁶Rb follows the distribution of cardiac output and from both these data the nutritional blood flow to the parts of the heart may be estimated.Cardiac output was similar in rats exposed to simulated high altitude later in life (newcomers) and in control animals, but it was significantly lower in rats born in the low pressure chamber (natives).Fractions of cardiac output supplying cardiac ventricles and septum in rats from both hypoxic groups were significantly higher than in control animals. In the natives they were significantly higher than in the newcomers. The fractions of cardiac output in both newcomers and natives remained significantly higher than those of the control animals, also when calculated per gram of heart tissue.Nutritional coronary blood flow (in ml/min) was higher in both ventricles and septum of the newcomers and in the right ventricle of the natives, and lower in the septum of the natives, when compared with control animals. Coronary blood flow per gram of heart tissue (in ml/min·g) was significantly higher in all cardiac parts of the newcomers, but it was about the same in all cardiac parts of the natives when compared with controls.The importance of observed changes concerning myocardial tissue oxygenation is analyzed by using Krogh's cylindrical tissue model.Presented in part at the XXVIth International Congress of Physiological Sciences, New Delhi, India, October 20–26, 1974.