WATER AND ELECTROLYTE METABOLISM IN INFANTS FED COW'S MILK MIXTURES DURING HEAT STRESS

Abstract

Complete balances of water, fat, N, Cl, Na, K, P and Ca were determined on normal infants during exposure to a hot and a cool environment. Milk diets were used offering different osmolar loads at the usual intakes of water per 100 calories. Two infants were fed on evaporated milk providing only 100 gm. of water per 100 calories. The data show that high evaporative water losses decrease urine volumes at hot environmental temperatures. At water intakes of 150 ml. per 100 calories, the usual cow's milk mixtures with or without added carbohydrate do not lead to urines approaching the physiological limitations of urinary concentration at 90° to 93°F.(32.2 to 33.9°C). Protein or electrolyte greater than evaporated milk induces more concentrated urines. Limitation of water to 100 gm. per 100 calories of evaporated milk induces maximal urinary concentration at this temperature and beginning symptoms of heat prostration. The water intake of these infants on this diet was large owing to high caloric food intake. Under the stimulation of the metabolism by high food intake and the limitation of water intake in relation to osmolar excretory load, heat balance could not be attained without concentrating body electrolyte. Recovery at a lower temperature occurred on this diet. The osmolar loads of infant food was discussed in relation to extrarenal losses of water. Low osmolar loads provide a margin Of safety if water intake is low, if extrarenal expenditure of water is high or if renal ability to concentrate the urine is limited. The osmolar load of cow's milk is such that reducing this load by dilution with water and addition of carbohydrate is indicated until the caloric concentration is that of human milk, i.e., 150 gm. of water per 100 calories.