Meal stimulation of albumin synthesis: a significant contributor to whole body protein synthesis in humans

Abstract

The present studies were performed to test the hypothesis that the liver, by increasing the synthesis of specific plasma proteins during the absorption of an amino acid meal, may play an important role in the temporary "storage" of ingested essential amino acids and to explore the effects of glucocorticosteroids and recombinant human growth hormone (rhGH) on these processes. The fractional synthetic rates of albumin and fibrinogen were determined using simultaneous infusions of intravenous [1-14C]leucine and intraduodenal [4,5-3H]leucine after 22 h fasting and during absorption of glucose and amino acids in four groups of normal subjects treated for 1 wk with placebo, prednisone (0.8 mg.kg-1.day-1), rhGH (0.1 mg.kg-1.day-1), or combined treatment. When compared with the fasted state and independent of the route of tracer delivery and hormonal treatment, albumin, but not fibrinogen, synthesis increased (P < 0.0001) during absorption of a mixed glucose amino acid meal in all groups. This increase in albumin synthesis accounted for 28% of the increase in whole body protein synthesis associated with feeding and for 24, 22, and 14% in the prednisone, rhGH, and combined treatment groups, respectively. These data suggest that the stimulation of albumin synthesis observed during feeding prevents irreversible oxidative losses of a significant fraction of ingested essential amino acids and may serve as a vehicle to capture excess dietary amino acids and transport them to peripheral tissues to sustain local protein synthesis.

Mechanisms of postprandial protein accretion in human skeletal muscle. Insight from leucine and phenylalanine forearm kinetics.

“…Our forearm catheterization data agree with one of these studies (6) as regards meal-induced acute stimulation of forearm protein synthesis. They agree also with previous findings obtained at the whole body level, as regards the simultaneous inhibition of endogenous proteolysis and the stimulation of protein synthesis after a mixed meal (3)(4)(5)(6)(7)(8)(9)(10)(11).…”

“…Several studies in humans have shown that meal ingestion is accompanied by both an increase of whole body protein synthesis and a suppression of protein degradation (3)(4)(5)(6)(7)(8)(9)(10)(11). However, the response to meal of protein kinetics in individual human body tissues is far less known.…”

“…However, the response to meal of protein kinetics in individual human body tissues is far less known. Synthesis of albumin, i.e., the most abundant plasma protein, was stimulated by a mixed meal (11). It is surprising, however, that possible changes of postprandial protein turnover occurring in skeletal muscle, i.e., the most abundant deposit of body proteins (12), have been scarcely investigated in humans.…”

Plasma Proteome Dynamics: Analysis of Lipoproteins and Acute Phase Response Proteins with 2H2O Metabolic Labeling

“…Stimulated synthesis of ApoB 100 suggests very low density lipoprotein secretion induced in response to an increased energy requirement of muscle and heart for very low density lipoprotein-bound TG. However, the synthesis of albumin, the most abundant plasma protein, is regulated by amino acid substrate availability in normal conditions (46). Although it is not clear why fasting reduces fibrinogen synthesis, a similar reduction in fibrinogen synthesis was observed in healthy human subjects after a short term increase in plasma free fatty acids by lipid infusion (47).…”

Exercise improves albumin fractional synthetic rate in chronic hemodialysis patients

“…Serum concentration of albumin is determined by its synthesis, breakdown, losses, volume of distribution and exchange between intra-and extravascular spaces (Klein, 1990;Jeejeebhoy, 1998). Nutritional supplementation has been shown to optimize anabolic activity of the liver to synthesize albumin in healthy subjects, possibly owing to increases in circulating insulin, which positively modulates albumin FSR (De Feo et al, 1992). Exercise is a potential treatment for wasting syndromes as it directs more nutrients toward muscle tissues and induces a greater sensitivity and responsiveness to metabolic events regulated by insulin compared with nutrient administration alone (Wasserman et al, 1991).…”