Five adult subjects, three male and two female, were given fructose-U-C-14 by single injection under the condition of fructose loading. The radioactivity in glucose was determined in serial arterial samples. On a separate day, glucose-6-C-14 was given to these same subjects under identical conditions. Using these two curves, the fructose converted to glucose was determined. In these subjects an average of 30.94 per cent of the infused fructose appeared as blood glucose.

Hepatic vein catheterization showed a large positive arteriovenous difference for fructose (50 to 80 per cent of infused fructose) and negative arteriovenous differences for glucose and lactate. There was a discrepancy between the calculated fructose conversion to glucose (30 per cent) from the tracer studies and the glucose production estimated from the hepatic arteriovenous differences of glucose (10 per cent). Supporting data for the validity of the former figure are given.

The simultaneous hepatic production of glucose and lactate by the liver is most likely due to the large substrate load of fructose entering the glycolytic scheme at a point which bypasses the rate limiting enzymes for both glycolysis and gluconeogenesis.

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