Respiration and lactate production in isolated frog skeletal muscle: effects of passive stretch

The effects of varying degrees of passive stretch on in vitro oxygen consumption and intracellular lactate efflux have been investigated in paired recti abdomini muscles from small male frogs. Oxygen consumption [mm3 (STP)/mg (dry wt)/hr] was found to be linearly related to load (r = 0.98), increasing from 1.57 +/- 0.11 (SE) at 2 g to 2.30 +/- 0.18 at 10 g, 2.89 +/- 0.16 at 20 g and 3.26 +/- 0.21 at 30 g. Lactate released into the medium [microM/g (dry wt)/hr] was inversely related to load (r = -0.52), increasing initially from 36.84 +/- 3.28 (SE) at 2 g to 108.55 +/- 12.9 at 10 g, then abruptly decreasing with additional loading (18.10 +/- 2.60 at 20 g and 11.71 +/- 2.80 at 30 g). Results suggest that as stretch-related oxidative energy metabolism increases, there is a lessening dependence on anaerobic energy-yielding processes.