Leucine uptake by splanchnic and leg tissues in man: relative independence of insulin levels.

The influence on leucine disposal of physiological alterations in plasma insulin concentrations was examined in three groups of healthy male subjects, six in each group. After an overnight fast the subjects received an intravenous infusion of either leucine (300 mumol/min for 150 min, series A), or leucine plus glucose (2.2 mmol/min, series B), or leucine, somatostatin (7 micrograms/min) and glucagon (1 ng/min, series C). Arterial concentrations of substrates and their net exchange across the splanchnic and leg tissues were determined with a catheter technique. Insulin concentrations rose from 12 +/- 2 to 20-22 mu-units/ml in series A, from 11 +/- 3 to 60-65 65 mu-units/ml in series B and decreased from 8 +/- 1 to approximately 5 mu-units/ml in series C. The basal leucine concentration for all subjects was 109 +/- 8 mumol/l and it rose progressively during the infusions. In series A, the level was 598 +/- 20 mumol/l after 150 min. The corresponding value was 542 +/- 38 mumol/l in series B and 651 +/- 25 mumol/l in series C. Significant differences were observed between series A and B (P less than 0.05) and series A and C (P less than 0.01) when data for 90-150 min of infusion were combined (analysis of variance). In all groups the leucine infusion resulted in an augmented net uptake of leucine across the leg (77-85 mumol/min) and across the splanchnic bed (61-72 mumol/min) but no significant intergroup differences were observed.(ABSTRACT TRUNCATED AT 250 WORDS)