Effect of lactate on FFA and glycerol turnover in resting and exercising dogs

The rates of appearance of FFA (RaFFA) and that of glycerol (RaGLY) were measured simultaneously with [1-¹⁴C]palmitate and [2-³H]glycerol, in dogs with indwelling arterial and venous catheters. Lipolysis was stimulated by exercise (treadmill run on 10% slope) or by the infusion of norepinephrine (0.5 μg/kg x min). Na-L(+) lactate (L), Na pyruvate (Py), or Na nicotinate (N) were infused. All 3 compounds decreased RaFFA. RaGLY was increased by L, unaltered by Py, and decreased by N. There was an inverse correlation (P < 0.001) between the logarithms of RaFFA and plasma lactate. A linear correlation was obtained between RaGLY and plasma lactate when this latter was increased by the infusion of L. It is suggested that lactate in physiological concentrations inhibits the release of FFA stimulated by exercise and the increase of the NADH/NAD ratio leads to the formation of α glycerophosphate which in turn yields glycerol. Therefore, changes in plasma glycerol do not reflect lipolysis when blood lactate increases. The effect of lactate on RaFFA can be explained by an enhanced reesterification, although a direct inhibition on lipase could not be excluded.