Oxygen consumption, along with lactic and pyruvic acid in blood, have been measured throughout the performance of heavy muscular exercise of different intensities, all leading to exhaustion in 1–10 min. Oxygen consumption increases exponentially with time; the maximum level attained seems to be independent of the intensity of exercise except in exercises of very high intensity and short duration, when it seems to be slightly increased. The rate of increase of oxygen consumption increases with the intensity of exercise. Pyruvic acid in blood increases exponentially also, and a steady state is reached at a level which tends to be higher, the heavier the exercise. Lactic acid increases as a linear function of time, the line eventually flattening down only toward the end of the exercise when the maximal values of lactic acid are reached. The lactic acid increase, grams per minute, is a linear function of the intensity of exercise; no lactic acid is produced if the exercise is below 220 cal/kg min, or a higher value for athletes. The caloric equivalent of lactic acid production from glycogen can be calculated at about 222 cal/g. This value in man is discussed in relation to previous values given. The kinetic of the lactic acid increase during exercise is in agreement with the hypothesis of an additional (alactacid) mechanism of oxygen debt contraction. Submitted on July 31, 1962

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Inulin and urea clearances were determined simultaneously on unanesthetized, undisturbed rats with catheters permanently inserted in the abdominal aorta, jugular vein, and urinary bladder. The rats were fed a) a normal Purina chow diet; b) a high-protein diet with normal salt content; or c) a high-protein diet with 2% NaCl added. Some rats on the high-protein, high-salt diet were given additional infusions of either urea or 5% amino acid solution. In the control animals, inulin clearances averaged 0.59 ml/min per 100 g body wt, and urea clearances averaged 0.39 ml/min per 100 g body wt. Significantly higher urea and inulin clearances were obtained on the other diets. Of 79 clearances determined on normal rats given the high-protein, high-salt diet, a total of 17 urea-to-inulin clearance ratios greater than one were obtained No urea-to-inulin clearance ratios greater than one were obtained with any of the other diets. Reasons are given in support of urea production or active secretion by the kidneys as the probable explanations for these results.

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