Cardiac resistance to the cardiotoxic effect of isoprenaline--ISO (single dose of 0.1 mg X kg-1) was studied in rats acclimatized to intermittent high altitude--IHA (barochamber, 8 h a day, 5 days a week, stepwise up to 7000 m). The extent of lesions was evaluated quantitatively by means of the increased accumulation of 203HgCl2. Five weeks' acclimatization was followed by a marked increase in the resistance of the myocardium to the necrogenic effect of ISO; this effect was more expressed in the left ventricle, so that the right to left difference generally observed under normoxic conditions disappeared. The increased resistance of the myocardium to ISO-induced damage persisted long after the animals had been returned to normoxic conditions; even six weeks after the last hypoxic exposure the sensitivity of the myocardium to damage had still not returned to the values of unacclimatized animals.

Right ventricular function in rats with hypoxic pulmonary hypertension