Physiological Significance of the Secretion of Endogenous Insulin into the Portal Circulation: V. The Quantitative Importance of the Liver in the Disposition of Glucose Loads

Previous studies from this laboratory," recently confirmed,' have shown that insulin administered in a manner which minimized the counter-regulatory responses to a falling blood glucose concentration resulted in a prompt decline in hepatic glucose output, which accounted in large part for the concomitant decrease in the glucose pool. The physiologic role of the liver in carbohydrate metabolism was defined further in studies which examined the effects of glucose loading on net hepatic glucose balance.' The administration of glucose resulted not only in a cessation of hepatic glucose output but also in a net uptake of glucose by the liver. This hepatic uptake of glucose occurred at a mean arterial glucose concentration only 36 mg. per 100 ml. above the fasting level and was apparently insulin dependent. The purpose of the present study was to determine the quantitative importance of the liver in the disposition of exogenous carbohydrate by examining the capacity of the liver to take up glucose during glucose loading. Four groups of dogs were studied; each subsequent group received a progressively greater glucose load, varying in different dogs from as little as 53 mg. per minute to as much as 1,037 mg. per minute. In order to measure hepatic rather than splanchnic glucose balance, dogs with chronic end-to-side portacaval shunts were used, since this operation separates the liver from the extrahepatic splanchnic circulation.