Effect of insulin on carbohydrate metabolism of skeletal muscle fibers and diaphragm from control and pancreatectomized rats.

Rat diaphragm muscle has been used almost exclusively for the investigation in vitro of skeletal muscle metabolism. However, the diaphragm is a specialized muscle adapted to constant activity and, with respect to oxygen consumption (1) and oxidative metabolism, seems to occupy an intermediate position between constantly active heart muscle and intermittently active skeletal muscle (2, 3). Histological examination demonstrates that diaphragm muscle is covered on both sides by complex mesothelial membranes (4, 5) that have an independent metabolism (6). For these reasons it seems that results obtained with diaphragm muscle should not be interpreted as typical of skeletal muscle. Therefore a technique for preparing viable muscle fiber groups from rats for use in comparison with diaphragm muscle in a Warburg apparatus was developed (7). With this technique it was found that the glucose uptake of adductor fibers from control rats was 81% of the value for the diaphragm, whereas the acetoacetic acid uptake was 23% of the value for the diaphragm. Both diaphragm and adductor fibers from alloxan diabetic rats took up less acetoacetic acid and glucose than diaphragm and fibers from control rats. In the present study the stimulating effect of insulin on glucose uptake, lactate and CO2 production, and glycogen synthesis in diaphragm muscle and in adductor fiber groups from control and diabetic rats has been described. In view of the general toxic effect of alloxan, partially pancreatectomized rats were used for the diabetic preparation.