Effect of Insulin on Transport of Glucose and Galactose Into Cells of Rat Muscle and Brain

Abstract

Normal, eviscerated and alloxan diabetic rats received glucose by continuous intravenous infusion with or without added insulin. In all cases insulin caused a marked rise in the free glucose content of the diaphragm and heart. In similar experiments, eviscerated rats were infused with galactose. Insulin caused a marked rise in the free galactose content of diaphragm, heart and gastrocnemius. In muscle, glucose and galactose were extracellular in the absence of insulin, but were largely intracellular in the presence of insulin. In brain, free intracellular galactose was found in equally large amounts in the presence or absence of insulin. These findings were interpreted as follows: (a) transport of glucose across the cell membrane is the rate limiting step for glucose uptake (and utilization) by muscle; (b) the transport of glucose and galactose is accelerated by insulin; (c). the transport is inhibited in alloxan diabetic muscle and can be accelerated by insulin; (d) the transport process in muscle is prior to and distinct from the hexokinase reaction; (e) the transport of galactose, and probably glucose, into the cells of brain tissue is not accelerated by insulln.