Leucine Uptake by Splanchnic and Leg Tissues in Man: Relative Independence of Insulin Levels

Abstract

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)

Kidney, splanchnic, and leg protein turnover in humans. Insight from leucine and phenylalanine kinetics.

“…This concept was supported not only by the leucine kinetic data but also by the behavior of net balance of several amino acids, which was negative in muscle but positive (i.e., in the direction of net uptake) across the splanchnic bed (Table II). This latter finding is in agreement with previous observations (30,57).…”

“…Splanchnic amino acid and protein turnover had been investigated previously in humans using a variety of techniques (1,4,12,13,29,30,45,46,57). In this study, we have compared splanchnic protein degradation and synthesis, net protein balance, leucine transmembrane exchange, oxidation, and bidirectional leucine interconversion with KIC with the corresponding rates measured across the kidneys and the legs in postabsorptive humans.…”

Insulin-mediated reduction of whole body protein breakdown. Dose-response effects on leucine metabolism in postabsorptive men.

“…In contrast, Eriksson et al (19) have suggested that leucine disposal is independent of plasma insulin concentrations. However, their protocol employed glucose and leucine infusions to stimulate pancreatic insulin release and the resultant hyperglycemia and elevated plasma leucine levels created a less controlled insulin stimulus than the present studies.…”

“…The important relationship between insulin and leucine metabolism is well established (1-3). In man, insulin accelerates the disposal of an exogenous load of leucine (19) and hyperinsulinemia inhibits the release of leucine from muscle (20). In vitro studies have demonstrated that insulin enhances the uptake of leucine by muscle (21), adipose tissue (22), and liver and kidney (23), and that insulin promotes protein synthesis (24,25).…”

The Effect of Hyperglycemic Hyperinsulinemia on Small‐Intestinal Mucosal Protein Synthesis in Patients After Surgical Stress

“…Thus, in healthy subjects glucose infusion did not alter duodenal protein synthesis 3 or splanchnic amino acid balances. 4 Correspondingly, various degrees of hyperinsulinemia remained without anabolic effects in the splanchnic bed. [5][6][7] Stimulatory effects on splanchnic protein synthesis were also absent when the insulin-induced hypoaminoacidemia was prevented by simultaneous amino acid infusion.…”