Chronic Consumption of a Low Sodium Diet: Hormonal and Physiological Effects During Exercise in the Heat,

Abstract : To elucidate the effects of sodium deficiency on the ability to work in the heat, immature rats were fed a diet deficient in sodium (Na+) for approximately 2 months. Rates of weight gain were severely affected (P.01) in the Na+ deficient rats (1.7 g/day vs. 7.2 g in controls) although fluid consumption was unaffected. The low Na+ diet effected no alterations in endurance or weight loss during exercise in the heat to hyperthermic exhaustion, but final core and skin temperatures were significantly reduced in the low Na+ group (p.02) and hemotocrit ratios were significantly (p.001) increased. Circulating Na+ and potassium (K+) levels were significantly (p.05) increased in both groups after hyperthermic exhaustion. In the Na+ deficient groups, plasma levels of both aldosterone and cortisol/corticosterone were significantly (p.05) increased, and these increments were exacerbated following exercise to hyperthermic exhaustion. Consumption of the low Na+ diet elicited significant increments in circulating levels of lactate (p.01) and creatinine (p.01), both of which were increased further after exercise. Circulating glucose was unaffected by consumption of the sodium deficient diet but declined in this group following exercise. Urea nitrogen and lactic acid dehydrogenase were increased after exercise but unaffected by the low sodium diet. Additional experiments are planned to elucidate further the metabolic and physiologic effects of chronic ingestion of a low Na+ diet.