Action of muscular work on transfer of sugars across cell barriers; comparison with action of insulin.

I T HAS BEEN KNOWN CliniCally for many years that intense muscular work increases the uptake of sugar from the blood, even in the untreated diabetic patient (I, 2). This has recently been studied in the diabetic anima1 by Ingle (3, 4) who showed that severe work can cause a drop in blood sugar to extremely low levels in diabetic animals receiving no insulin. He has also demonstrated that at the work intensities which he used, the effect of insulin and of work were additive. On the basis of recent work on the action of insulin, we have postulated that this hormone effects a system which serves to transfer sugars of a definite chemical configuration from the extracellular fluid compartment into certain cells (muscle) (5, 6). Some of the sugars responsive to the action of insulin are not utilizable by muscle. Under the influence of the hormone, they acquire a wider volume of distribution. Because of the similarity of the action of work to that of insulin in respect to blood glucose, we were led to investigate whether, like insulin, it would affect the entry of sugars on the basis of chemical configuration irrespective of utilization. In other words, does work, as well as insulin, act upon some ‘cell surface barrier’ which is the specific determining factor for the entry of sugars.