Studies on the utilization and mobilization of lipid in skeletal muscles from streptozotocin-diabetic and control rats.

Several aspects of lipid metabolism in the soleus and diaphragm muscles of streptozotocin-diabetic and control rats were investigated. The triglyceride content of both muscles was elevated in the diabetic state and the presence of increased intracellular lipid was confirmed by electron microscopy. In vitro glucose and palmitate oxidation studies showed that both types of muscle from the diabetic animals metabolized more fat than did the soleus and diaphragm from control rats. While isoproterenol alone produced a significant lipolytic response in both the soleus and diaphragm from control and diabetic animals, there was no difference in the percent increase in fatty acids released from muscles of diabetic rats compared to controls. However, the absolute difference was greater when the diaphragms were compared. Muscles from experimental and control animals showed a marked reduction in the amount of free fatty acids released in response to insulin. In addition, in the presence of the hormone, both the absolute and percent isoproterenol-stimulated increases in fatty acids were significantly greater for both diaphragm and soleus muscles from diabetic rats. The effects of insulin, isoproterenol, and the combination of these two hormones on the amount of glycerol released into the incubation medium were similar to those found on free fatty acid release. The results of these experiments show that there is an apparent increase in fat utilization in skeletal muscle of diabetic rats. Furthermore, measurements of triglyceride concentration and the enhanced response to isoproterenol stimulation in the muscles from these animals suggests that they may have an increased capacity for mobilization of intracellular lipids. Finally, in the diabetic state, both the soleus and diaphragm appear to demonstrate an increased response to the antilipolytic effect of insulin as measured by the decreased amount of fatty acid released into the incubation medium, the percent change also being significant for the soleus muscle.-Stearns, S. B., H. M. Tepperman, and J. Tepperman. Studies on the utilization and mobilization of lipid in skeletal muscles from streptozotocin-diabetic and control rats.