Influence of Age on Rate of Respiration of Sliced Cardiac Muscle

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Abstract
Slices of cardiac ventricular muscle of guinea pigs respire for the 1st 15 min. of incubation at a rate which does not change significantly during the life span of this sp. The decline of the metabolic rate from this initial to a steady level, a phenomenon observed previously in cardiac slices, becomes more pronounced and prolonged from the time of birth until the age of 5-6 mos. when growth is nearly completed. Consequently, the steady level respiration decreases during growth. The decline of the rate of respiration to a steady level is ascribed to damage resulting from slicing; its stabilization at the steady level to continued activity of mechanically uninjured muscle fibers or possibly other functional cardiac units. The length of these units can roughly be estimated from the slice thickness and the ratio of initial to steady level rate of respiration and can thus be seen to increase during the growth period.