Effect of mixed meal ingestion on fuel utilization in the whole body and in superficial and deep forearm tissues

Six healthy lean male adults, given a mixed meal containing 3190 kJ (16 % f rom protein, 44 % from carbohydrate and 40 % from fat) were studied for the next 370 min using arteriovenous cannulation techniques across superficial and deep forearm tissues. The meal produced no significant change in forea rm blood flow or skin temperature. The major differences between superficia l and deep forearm tissues were (a) creatinine release by deep tissues but not superficial tissues; (b) the release of non-esterified fatty acids (NEF A) by superficial tissues and uptake by deep tissues; and (c) the more prol onged large positive arteriovenous concentration difference for glucose acr oss deep than superficial tissues. The similarities were (a) general patter n of individual amino acid exchanges and transient positive amino acid N ba lance after meal ingestion; (b) consistent uptake of glutamate and release of glutamine (the main carrier of N out of superficial and deep forearm tis sues); (c) the magnitude of the arteriovenous concentration differences for glucose, NEFA and total amino acids were related to the changes in their c irculating concentrations and to the oxidation of carbohydrate, fat, and pr otein in the whole body; and (d) increases in the arterio-deep venous and a rterio-superficial venous differences for glucose did not result in increas ed release of lactate, alanine or pyruvate, implying no increase in the act ivity of glucose-lactate and glucose-alanine cycles between forearm tissues and the liver. This study suggests that in a number of ways superficial an d deep tissues can be regarded, at least qualitatively, as behaving as a 's ingle metabolic unit'.