AVAILABILITY OF GLUCOSE INGESTED DURING MUSCLE EXERCISE PERFORMED UNDER ACIPIMOX-INDUCED LIPOLYSIS BLOCKADE

This study investigated the percentage of carbohydrate utilization tha n can be accounted for by glucose ingested during exercise performed a fter the ingestion of the potent lipolysis inhibitor Acipimox. Six hea lthy male volunteers exercised for 3 h on a treadmill at about 45% of their maximal oxygen uptake, 75 min after having ingested 250 mg of Ac ipimox. After 15-min adaptation to exercise, they ingested either gluc ose dissolved in water, 50 g at time 0 min and 25 g at time 60 and 120 min (glucose, G) or sweetened water (control, C). Naturally labelled [C-13]glucose was used to follow the conversion of the ingested glucos e to expired-air CO2. Acipimox inhibited lipolysis in a similar manner in both experimental conditions. This was reflected by an almost comp lete suppression of the exercise-induced increase in plasma free fatty acid and glycerol and by an almost constant rate of lipid oxidation. Total carbohydrate oxidation evaluated by indirect calorimetry, was si milar in both experimental conditions [C, 182, (SEM 21); G, 194 (SEM 1 6) g . 3 h(-1)], as was lipid oxidation [C, 57 (SEM 6); G, 61 (SEM 3) g . 3 h(-1)]. Exogenous glucose oxidation during exercise G, calculate d by the changes in C-13 : C-12 ratio of expired air CO2, averaged 66 (SEM 5) g . 3 h(-1) (19% of the total energy requirement). Consequentl y, endogenous carbohydrate utilization was significantly smaller after glucose than after placebo ingestion: 128 (SEM 18) versus 182 (SEM 21 ) g . 3 h(-1), respectively (P < 0.05). Symptoms of intense fatigue an d leg cramps observed with intake of sweet placebo were absent with gl ucose ingestion. In conclusion, we found glucose ingestion during 3-h exercise with lipolysis blockade could provide metabolic substrate per mitting a significant Sparing of endogenous carbohydrate and consequen tly an improvement in performance.