Endurance training affects lactate clearance, not lactate production.
Primed-continuous infusion of [2-3H]- and [U-14C]lactate was used to study the effects of endurance training (running 2 h/day at 29.4 m/min up a 15% gradient) on lactate metabolism in rats. Measurements were made under three metabolic conditions: rest (Re), easy exercise (EE, 13.4 m/min, 1% gradient) and hard exercise (HE, 26.8 m/min, 1% gradient). Blood lactate levels in trained animals increased from 1.0 +/- 0.09 mM in Re to 1.64 +/- 0.21 in EE and 2.66 +/- 0.38 in HE. Control animals also demonstrated an increase in blood lactate with increasing work rate, but values were 1.93 +/- 0.21 and 4.62 +/- 0.57 mM at EE and HE, respectively. Lactate turnover rates (RtLA) measured with [U-14C]lactate increased from 214.0 +/- 17.0 mumol.kg-1.min-1 in Re to 390.3 +/- 31.6 in EE and 518.1 +/- 56.4 in HE. No significant differences in RtLA were observed between controls and trained animals under any condition. Identical relationships between RtLA and exercise or training were obtained with [2-3H]lactate; however, the values obtained were consistently 90% higher than those observed with [U-14C]lactate. Metabolic clearance rate (MCR) for 14C was not significantly different in Re between controls and trained animals (180.6 +/- 27.7 ml.kg-1.min-1). Metabolic clearance of lactate in trained animals was 37 and 107% greater than in controls during EE and HE, respectively. Results indicate that the effect of endurance training is not on production of lactate but on its clearance from the blood.
D000818:Animals; D002245:Carbon Dioxide; D005260:Female; D005943:Gluconeogenesis; D007700:Kinetics; D007773:Lactates / Q000096:biosynthesis / Q000378:metabolism*; D019344:Lactic Acid; D008657:Metabolic Clearance Rate; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal; D010807:Physical Endurance; D051381:Rats; D011919:Rats, Inbred Strains
D007773:Lactates; D002245:Carbon Dioxide; D019344:Lactic Acid