Lipolysis and fat oxidation decrease during postprandial lactatemia
Authors: Osmond Adam , Leija Robert , Arevalo Jose , Curl Casey , Duong Justin , Brooks George 
Published: May 2024

Circulating glycerol ([glycerol]) and free fatty acid ([FFA]) 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. We hypothesized that whole-body lipolytic (i.e., glycerol rate of appearance, Ra) and fat oxidation (FOx) rates would decrease following oral glucose consumption and inversely correlate with an increase in [lactate] above baseline levels (i.e., lactatemia) during both enteric (0–30 min) and systemic (60–120 min) phases of the postprandial lactate shuttle (PLS). Young, healthy men and women (n=15) reported to the lab following a 12-hour overnight fast and had the 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). Glycerol Ra was significantly lower at 5 min (1.92 ± 0.12 μmol·kg−1·min−1) and 30–120 min during the OGTT compared to baseline (2.06 ± 0.12 μmol·kg−1·min−1). [Glycerol] was significantly lower from baseline (69.19 ± 2.50 μM) at 30 min (50.58 ± 3.01 μM) after glucose consumption, then continued to decline thereafter. Similarly, [FFA] was significantly lower from baseline (464.71 ± 27.01 μM) at 30 min (247.14 ± 32.78 μM), then continued to decline. FOx was significantly lower from baseline (0.89 ± 0.05 kcal∙min−1) at 60 min (0.58 ± 0.05 kcal∙min−1) and remained steady from then on. Concurrently, [lactate] increased from baseline (0.59 ± 0.06 mM) and was significantly higher at 5 min (0.71 ± 0.06 mM) after glucose consumption, peaked at 15 min (1.09 ± 0.01 mM), reached a nadir at 30 min, then continued to rise thereafter. There was an overall inverse correlation (r = -0.71, p = 0.07) between glycerol Ra and [lactate] during the OGTT that was also present during the enteric phase (r = -0.45, p = 0.55). Similarly, there was overall an inverse correlation between FOx and [lactate] (r = -0.57, p = 0.17), but it was not present during the enteric phase (r = 0.93, p = 0.07). However, the correlations of both glycerol Ra and FOx with [lactate] approached linearity during the systemic phase (r = 0.99, p = 0.06). The reduction in glycerol Ra at 5 min indicates a rapid decrease in the rate of lipolysis following oral glucose consumption. The correlations suggest that lactatemia may influence both glycerol Ra and FOx by exerting an inhibitory effect, particularly during the systemic phase of the PLS. However, the lag in the decrease in FOx and opposing responses of glycerol Ra and [lactate] at 5 min suggests that lactatemia may have a greater role in inhibiting whole-body lipolysis in the postprandial period. Supported by NIH grant R01 AG059715 to GAB. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.