Lactate and glucose interactions during rest and exercise in men: effect of exogenous lactate infusion - PubMed (original) (raw)

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Lactate and glucose interactions during rest and exercise in men: effect of exogenous lactate infusion

Benjamin F Miller et al. J Physiol. 2002.

Abstract

To test the hypothesis that lactate plays a central role in the distribution of carbohydrate (CHO) potential energy for oxidation and glucose production (GP), we performed a lactate clamp (LC) procedure during rest and moderate intensity exercise. Blood [lactate] was clamped at approximately 4 mM by exogenous lactate infusion. Subjects performed 90 min exercise trials at 65 % of the peak rate of oxygen consumption (V(O(2))(,peak); 65 %), 55 % V(O(2))(,peak) (55 %) and 55 % V(O(2))(,peak) with lactate clamped to the blood [lactate] that was measured at 65 % V(O(2))(,peak) (55 %-LC). Lactate and glucose rates of appearance (R(a)), disappearance (R(d)) and oxidation (R(ox)) were measured with a combination of [3-(13)C]lactate, H(13)CO(3)(-), and [6,6-(2)H(2)]glucose tracers. During rest and exercise, lactate R(a) and R(d) were increased at 55 %-LC compared to 55 %. Glucose R(a) and R(d) were decreased during 55 %-LC compared to 55 %. Lactate R(ox) was increased by LC during exercise (55 %: 6.52 +/- 0.65 and 55 %-LC: 10.01 +/- 0.68 mg kg(-1) min(-1)) which was concurrent with a decrease in glucose oxidation (55 %: 7.64 +/- 0.4 and 55 %-LC: 4.35 +/- 0.31 mg kg(-1) min(-1)). With LC, incorporation of (13)C from tracer lactate into blood glucose (L GNG) increased while both GP and calculated hepatic glycogenolysis (GLY) decreased. Therefore, increased blood [lactate] during moderate intensity exercise increased lactate oxidation, spared blood glucose and decreased glucose production. Further, exogenous lactate infusion did not affect rating of perceived exertion (RPE) during exercise. These results demonstrate that lactate is a useful carbohydrate in times of increased energy demand.

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Figures

Figure 1

Figure 1. Concentrations of blood lactate (A) and glucose (B) over time in response to exogenous lactate infusion (LC) and corresponding non-infusion control trials during rest and exercise

Values are means ±

s.e.m

.; n = 6. Squares, rest; diamonds, 65 % _V̇_O2,peak; circles, 55 % _V̇_O2,peak; filled symbols, control; open symbols, lactate clamp. ∧ Significantly different over time of exercise (P < 0.05).

Figure 2

Figure 2. Isotopic enrichment (IE) of M+1 lactate (A), M+1 glucose (B), M+2 glucose (C) and M+1 HCO3− (D) in response to exogenous lactate infusion (LC) and corresponding non-infusion control trials during rest and exercise

Values are means ±

s.e.m

.; n = 6. Squares, rest; diamonds, 65 % _V̇_O2,peak; circles, 55 % _V̇_O2,peak; filled symbols, control; open symbols, lactate clamp.

Figure 3

Figure 3. Lactate and glucose rates of appearance (_R_a; A), disappearance (_R_d; B) and metabolic clearance rate (MCR; C), in response to exogenous lactate infusion (LC) and corresponding non-infusion control trials during rest and exercise

Values are means ±

s.e.m

.; n = 6. Filled bars, endogenous lactate; hatched bars, exogenous lactate; open bars, glucose. # Significantly different from corresponding control (P < 0.05); + significantly different from rest (P < 0.05); * significantly different from 65 % (P < 0.05). Note in A, exogenous lactate infusion and endogenous lactate _R_a are additive.

Figure 4

Figure 4. Partitioning of total carbohydrate oxidation (glucose, lactate and muscle glycogen) in absolute (_R_ox; A) and relative (percentage of total; B) terms

Values are means ±

s.e.m

.; n = 6. Hatched bars, calculated muscle glycogen oxidation; open bars, tracer-determined glucose oxidation; filled bars, tracer-determined lactate oxidation; LC, lactate clamp. # Significantly different from corresponding control (non-LC) (P < 0.05); + significantly different from rest (P < 0.05).

Figure 5

Figure 5. Partitioning of total (hepatic plus renal) glucose production (GP) in absolute (A) and relative (B) terms during rest and exercise

Values are means ±

s.e.m

.; n = 6. Open bars, lactate incorporation into glucose (L → GNG); filled bars, calculated glycogenolysis (GLY); LC, lactate clamp. # Significantly different from corresponding control (non-LC) (P < 0.05); + significantly different from rest (P < 0.05).

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