EFFECTS OF NICOTINIC-ACID ON RESPIRATORY EXCHANGE RATIO AND SUBSTRATELEVELS DURING EXERCISE

The purpose of this study was to investigate the effects of pharmacolo gic treatment with nicotinic acid (NA) (3 g NA.d-1) on fuel utilizatio n during exercise and on total and HDL-cholesterol levels of trained r unners. Eight experienced male runners performed four 30-min submaxima l treadmill runs (SUB) at approximately 60% of aerobic capacity: the f irst served as the control condition, whereas SUBs 2, 3, and 4 were co nducted at the onset, midpoint, and conclusion of the 3-wk NA treatmen t period. A 1-g NA dose was ingested 1 h prior to SUBs 2-4, which were conducted in the morning following a 12-h fast. The respiratory excha nge ratio (RER) was significantly higher during SUBs 2, 3, and 4 (0.91 9 +/- 0.009, 0.898 +/- 0.007, and 0.896 +/- 0.009, respectively) than during SUB1 (0.871 +/- 0.008); and the RER during SUB2 was also signif icantly higher than that during SUB3 and SUB4 (P < 0.001). Serum free fatty acid (FFA) and glycerol levels were significantly lower during S UBs 2, 3, and 4 as compared with SUB1 (P < 0.001). Total cholesterol s howed a significant decrease (from 195.3 +/- 9.2 to 174.5 +/- 9.2 mg.d l-1) and HDL cholesterol showed a significant elevation (from 56.2 +/- 2.9 to 63.0 +/- 3.9 mg.dl-1) during the NA treatment period (P < 0.05 ). The RER, FFA, and glycerol data demonstrate a persistent inhibition of fat utilization during submaximal exercise due to NA treatment. Th e 3-wk NA treatment period also proved to be sufficient to effect chan ges in total and HDL-cholesterol levels of these runners.