Quantitation of glycolysis and skeletal muscle glycogen synthesis in humans

Abstract

We measured the net rates of skeletal muscle glycogen synthesis and glycolysis (conversion of [3-3H]glucose to 3H2O) in healthy overnight-fasted volunteers. Two studies were performed. In study 1, seven subjects participated in two paired infusions under basal conditions of either [2-3H]glucose (H2) or [3-3H]glucose (H3). Total glucose uptake (Rd) and rates of whole body 3H2O formation (3H2O Ra) were measured. With H2, Rd and 3H2O Ra were similar. With H3, 3H2O Ra, equal to glycolysis, was 65% of Rd. In study 2, six different subjects underwent a 3-h, 40 mU.m-2 x min-1 euglycemic insulin clamp. [6,6-2H2]glucose was infused throughout and H3 was infused during the last hour of the study. Open muscle biopsies were obtained at 150 and 180 min. Glycogen synthesis was assessed by three independent means: 1) direct measurement, as 3H disintegrations per minute in isolated muscle glycogen per plasma H3 specific activity; 2) extrapolation from the activity of glycogen synthase assayed in the presence of the concentrations of glucose 6-phosphate and UDP-glucose measured in the biopsy; and 3) the difference between Rd and glycolysis. Despite a wide range in Rd [24.5-58.8 mumol.kg fat-free mass (FFM)-1 x min-1] and glycolysis (14.2-26.1), the three methods yielded similar results of 20.0 +/- 3.9, 22.5 +/- 3.7, and 20.6 +/- 3.7 mumol.kg FFM-1 x min-1 and correlated highly with each other (r2 = 0.92-0.96). Our results (study 1) indicate that the rate of plasma tritiated water formation reflects the intracellular detritiation of tritiated glucose. Under hyperinsulinemic conditions (study 2) the net rate of muscle glycogen synthesis can be accurately estimated from the glycogen synthase activity and from the difference between total glucose uptake and glycolysis. Thus, at high physiological plasma insulin concentrations resulting in submaximal stimulation of muscle glycogen synthesis, the latter can be accurately measured in humans.

Defective glucose and lipid metabolism in human immunodeficiency virus-infected patients with lipodystrophy involve liver, muscle tissue and pancreatic β-cells

“…In HIV-negative individuals, EGS has been shown to be an index of glycogen storage (27). In the present study of normoglycaemic HIV-infected patients, the two surrogate parameters of glycogen deposition, i.e.…”

Endogenous glucose production increases in response to metformin treatment in the glycogen-depleted state in humans: a randomised trial

“…In the final 4 h period, EGP was assumed to equal Ra. The in vivo glycolytic flux rates were calculated from the generation rates of plasma 3 H 2 O from [3-3 H]glucose, assuming that all tritium in the C-3 position was lost to water during the glycolytic process as previously described in detail [23]. Non-oxidative glucose metabolism (NOGM) was calculated as the difference between Rd and glucose oxidation.…”

Effects of Troglitazone in Young First-Degree Relatives of Patients With Type 2 Diabetes

“…Briefly, this measurement is based on the knowledge that essentially all tritium in the C-3 position is lost to water at the level of the trioseisomerase reaction during the glycolytic process. Thus, the glycolytic flux rate can be calculated by multiplying the slope of the regression line obtained from the plot between time and 3 H 2 O content (in counts per minute per milliliter per minute) with total body water (in milliliters) estimated from the bioimpedance measurement and divided by plasma specific activity (in counts per minute per milligram) (31). In these calculations, plasma water was assumed to be 93% of the total plasma volume (31).…”

“…Thus, the glycolytic flux rate can be calculated by multiplying the slope of the regression line obtained from the plot between time and 3 H 2 O content (in counts per minute per milliliter per minute) with total body water (in milliliters) estimated from the bioimpedance measurement and divided by plasma specific activity (in counts per minute per milligram) (31). In these calculations, plasma water was assumed to be 93% of the total plasma volume (31). Linearity (before/after) of the accumulation of plasma-tritiated water radioactivity was obtained from Ϫ100 to 0 min during basal measurements (r ϭ 0.95 Ϯ 0.01/0.95 Ϯ 0.01 and 0.93 Ϯ 0.01/0.95 Ϯ 0.01) and from 40 to 180 min during insulin infusion (r ϭ 0.97 Ϯ 0.01/0.96 Ϯ 0.01 and 0.97 Ϯ 0.01/0.96 Ϯ 0.01) in the troglitazone and placebo groups, respectively.…”