The forearm and leg perfusion techniques in man do not give the same metabolic information

The present study evaluates whether forearm and leg perfusion techniques give the same metabolic information. Seven patients hospitalized for operation of uncomplicated disease were investigated pre-operatively in the fasted state, while seven other patients who were on intravenous nutrition were studied in the fed state. Blood flow and the extremity exchange of glucose, lactate, glycerol, free fatty acids and amino acids were measured simultaneously across the forearm and the leg in all individuals. In the fasted state the arteriovenous difference (a-v) of glucose uptake was statistically significant across the forearm while it was statistically insignificant across the leg (0.27 +/- 0.06 vs. -0.04 +/- 0.13 mmol l-1). The a-v differences of glycerol (0.025 +/- 0.028 vs. -0.043 +/- 0.013 mmol l-1) and free fatty acids 0.10 +/- 0.03 vs. -0.10 +/- 0.04 mmol l-1) were positive across the forearm while they were negative across the leg (P less than 0.01). In the fasted state the a-v difference of oxygen uptake (3.93 +/- 0.67 vs. 3.21 +/- 0.44 mmol l-1) and blood flow (4.1 +/- 1.0 vs. 4.0 +/- 0.7 ml min-1 100 g-1) did not differ between the arm and the leg, but the a-v difference in carbon dioxide production was significantly higher (P less than 0.05) across the forearm (2.43 +/- 0.37 vs. 1.29 +/- 0.29 mmol l-1) compared to the leg. In the fed state all the above-mentioned differences between forearm and leg became statistically insignificant. In the fed state the a-v difference of the sum of all amino acids was not significantly different from zero balance across the forearm (-146 +/- 103 mmol l-1) while there was a significant release from the leg (-175 +/- 6 mmol l-1, P less than 0.05). In the fed state the flux of the sum of all amino acids became significantly positive across the arm while it was not significantly different from zero balance across the leg. In the fed state, forearm blood flow was significantly higher than leg blood flow (6.2 +/- 0.5 vs. 4.0 +/- 0.2 ml min-1 100 g-1, P less than 0.001). The results in the present study demonstrate that the metabolic balance across regions of peripheral tissues may simultaneously differ considerably, i.e. being positive across the forearm and negative across the leg. This fact may imply that some previous claims may need reconsideration about 'peripheral tissue metabolism' associated with a certain clinical condition.