Free fatty acid availability and temperature regulation in cold water

The purpose of this study was to investigate whether a reduced availability of plasma free fatty acids (FFA) would impair human temperature regulation during cold exposure. Seven seminude male subjects were immersed on two occasions in 18 degrees C water for 90 min or until their rectal temperature (Tre) decreased to 35.5 degrees C. The immersion occurred after 2 h of intermittent oral ingestion of either nicotinic acid (NIC) or a placebo (PLAC). Plasma FFA levels immediately before the immersion were significantly lower in NIC (87 +/- 15 mumol/l) than in PLAC (655 +/- 116 mumol/l, P less than 0.05). Although FFA levels increased by 73% in NIC during the immersion (P less than 0.05), they remained significantly lower than in PLAC (151 +/- 19 vs. 716 +/- 74 mumol/l, P less than 0.05) throughout the immersion. Muscle glycogen concentrations in the vastus lateralis decreased after cold water immersion in both trials (P less than 0.05), but the rate of glycogen utilization was similar, averaging 1.00 +/- 0.27 mmol glucose unit.kg dry muscle-1.min-1). Plasma glucose levels were significantly reduced after immersion in both trials (P less than 0.05), this decrease being greater in NIC (1.3 +/- 0.2 mmol/l) than in PLAC (0.7 +/- 0.1 mmol/l, P less than 0.05). O2 uptake increased to 3.8 +/- 0.3 times preimmersion values in both trials (P less than 0.05). Mean respiratory exchange ratio (RER) immediately before the immersion was greater in NIC (0.87 +/- 0.02) than in PLAC (0.77 +/- 0.01, P less than 0.05). Cold exposure increased RER in PLAC but not in NIC.(ABSTRACT TRUNCATED AT 250 WORDS)