Regression of myocardial hypertrophy in the rat following removal of acute or chronic hypobaric hypoxia

Regression of myocardial hypertrophy in adult female rats exposed to hypobaric hypoxia was investigated. In particular the behaviour of the right and the left ventricles was studied after the removal of animals from short or long-term hypoxia (0.40 atm. of air/24 h or 0.40 atm./18 h daily for seven days). Changes in the myocardial mass were evaluated on the basis of the dry heart weight and expressed as mg/100 g of total body weight (mean ± s.e.m.). Both right and left ventricles show a significant increase in weight compared to room pressure controls when evaluated at the end of the hypoxic stimulus. Right and left ventricular weights fell after removal of the hypoxic stimulus, and were within the normal range by 72 h in the case of acute hypoxia and by 96 h in the case of chronic hypoxia. In conclusion, our data show that: (1) both acute and chronic hypobaric hypoxia caused a significant degree of myocardial hypertrophy in rats p < 0.001; (2) the hypertrophic process involved both ventricles (the right more than the left); (3) the removal of the hypoxic stimulus led to the disappearance of hypertrophy when evaluated as an increase in dry heart weight; (4) the time of the regression was related to the duration of hypoxia.