Capillary Supply and Utilization of Intracellular Oxygen in the Left Ventricular Myocardium from Rats Adapted to High Altitude

Abstract

The chronical exposure of young rats to a simulated altitude of 3500 m results in number of functional adaptations (Grandtner et al., 1974; Turek et al., 1972a). As concerns the heart, a multiplication of capillaries have been noted under chronical hypoxia (Turek, 1972b); Friedman et al., 1973). The stay in the hypoxic chamber leads also to an increase of the heart weight (heart hypertrophy). However, the extent of the latter can vary considerably: in rats born and rised in the hypoxic conditions (“natives”) a bilateral cardiac hypertrophy regularly occurs (Turek et al., 1972b). In those born at sea level and exposed to the same hypoxia fran their youth only (“newcaners”), the increase of the heart weight is restricted exclusively to the right ventricle (Grandtner et al., 1974). In addition, the hearts of the above two groups differ from functional point of view. While in the “natives” the cardiac output is 50 per cent depressed, it is elevated in the “newcaners” (Turek et al., 1972a). The amount of kinetic work supplied by 1 g of the left ventricular myocardium is therefore significantly higher in hearts of the latter animals. This elevated work output of the heart is apparently enabled by higher rates of the oxidative energy production. An increase in the glycolytic fluxes (Hochachka et al., 1977) as well as the accumulation of respiratory enzymes in heart homogenate (Shertzer et al., 1972; Tappan et al., 1957) may underlie such an adaptation to chronical hypoxia. In this work we tried to assess the kinetic aspects of mitochondrial function using the optical methods developed by Chance (Chance, 1976; Sugano et al., 1974). The hearts from rats exposed to the early (“natives”) and to the late (“newcomers”) hypoxia were compared. The left ventricular vascularization was also studied in these two groups by a new morphanetric approach (Rakusan et al., 1980) derived from the work of Loats et co-workers (Coats et al., 1978).