Delayed and diminished postprandial lactate shuttling in healthy older men and women

Abstract

Lactate, a product of glycolysis, is formed under aerobic conditions. Extensive work has shown lactate flux in young and exercising humans; however, the effect of age is not known. We tested the hypothesis that postprandial lactate shuttling (PLS) would be diminished in older adults. We used [3-13C]lactate and [6,6-2H]-glucose tracers, an OGTT, and arterialized blood sampling to determine postprandial lactate rates of appearance (Ra), disappearance (Rd), and oxidation (Rox) in 15 young (28.1 ± 1.4 yr) and 13 older (70.6 ± 2.4 yr) healthy men and women. In young participants fasting blood [lactate] [» 0.5 mM] rose after the glucose challenge, peaked at 15 min, dipped to a nadir at 30 min, and rose again peaking at 60 min [» 1.0mM]. Initial responses in lactate Ra of older participants were delayed and diminished until 90 minutes rising by 0.83 mg·kg-1·min-1. Lactate Rox was higher throughout the entire trial in young participants by a difference of approximately 0.5 mg·kg-1·min-1. Initial peaks in lactate Ra and concentration in all volunteers demonstrated presence of an enteric PLS following an OGTT. Notably, in the systemic, but not enteric PLS phase, lactate Ra correlated highly with glucose Rd (r2 = 0.92). Correspondence of second peaks in lactate Ra and concentration and glucose Rd show dependence of lactate Ra on glucose Rd. While results show both enteric and systemic PLS phases in young and older study cohorts, metabolic responses were delayed and diminished in healthy older individuals.