Aging Reduces Lipolysis During Postprandial Lactatemia

Circulating glycerol and free fatty acid concentrations decrease and lactate concentration ([Lactate]) increases in response to oral glucose consumption, but the effect of increased [Lactate] on the rate of lipolysis is not known. Moreover, it is not known if aging further modulates lipolytic rates following oral glucose consumption. PURPOSE: To determine whole-body lipolytic rate (glycerol rate of appearance, Ra) following oral glucose consumption in aging, and its relationship to changes in [Lactate] above baseline levels (lactatemia). METHODS: Fifteen young and 14 older healthy men and women reported to the lab following a 12-hr overnight fast and had a forearm vein catheterized for primed continuous infusion of [1,1,2,3,3-2H]glycerol. The contralateral hand vein was warmed and catheterized for arterialized blood sampling. After a 90-min equilibration period, participants underwent a 75 g oral glucose tolerance test (OGTT). Comparisons were made using two-way ANOVA with repeated measures. Data are presented as mean ± SEM. Correlations between glycerol Ra and [Lactate] were assessed using Pearson coefficients. RESULTS: Glycerol Ra in young participants was significantly lower 5 min (1.92 ± 0.12 μmol·kg-1·min-1, p = 0.04) and 30-120 min (≤1.69 ± 0.11 μmol·kg-1·min-1, p < 0.001) during the OGTT compared to baseline (2.06 ± 0.12 μmol·kg-1·min-1). Glycerol Ra in older participants was significantly lower 30-120 min (≤1.38 ± 0.11 μmol·kg-1·min-1, p ≤ 0.003) during the OGTT compared to baseline (1.77 ± 0.13 μmol·kg-1·min-1). [Lactate] in young participants was significantly higher throughout the OGTT compared to baseline (≥0.71 ± 0.05 vs. 0.60 ± 0.05 mM, p ≤ 0.04). [Lactate] in older participants was significantly higher 15-120 min (≥0.90 ± 0.06 mM, p ≤ 0.04) during the OGTT compared to baseline (0.65 ± 0.02 mM). There were no group differences in glycerol Ra or [Lactate]. However, there was an inverse relationship between glycerol Ra and [Lactate] in both groups that was stronger in older participants (r = -0.93, p = 0.002 vs. r = -0.71, p = 0.07). CONCLUSIONS: Lipolysis decreases in response to oral glucose consumption, but the reduction was delayed in older participants. Moreover, the correlations suggest that lactatemia exerts an inhibitory effect on lipolysis, and that the effect is greater in older participants. Supported by NIH grant R01 AG059715-01 to GAB.