Effect of Insulin and of Muscular Exercise on Protein Metabolism.

Abstract

The total urinary nitrogen was determined in hourly periods on normal fasting female dogs weighing 6 to 20 kilos. The urine was collected by catheter and the bladder thoroughly rinsed each time. After 3 preliminary control hours, insulin (usually 5 units per kilo of body weight) was injected subcutaneously and the urine collected for 3 or 4 periods until sugar was given to the animal to relieve the hypoglycemic convulsions.

The changes in protein metabolism after the insulin depended upon the nutritive condition of the animal. After short fasting periods of 1 to 5 days insulin increased the nitrogen excretion. In a typical case, on the second day of fast, the increase was from an average of 99 mg. per hour during the preliminary hours to 137 mg. after insulin. With a longer fasting period of 7 to 14 days, insulin produced no effect, for example 101 mg. per hour before and 100 mg. after the injection. When carbohydrate (50 to 100 gm. of sucrose) was administered every 3 or 4 days to an otherwise fasting animal, the injection of insulin produced the same increase in nitrogen excretion on the 16th as on the 2nd day of fast. Similar results were obtained on a dog in which muscular movement was prevented by amytal anesthesia.

Two fasting dogs were run daily on a treadmill to observe the effect on protein metabolism of decreasing the body carbohydrate through muscular exercise. After 4 hourly preliminary control periods the dogs were exercised for 3 half hour periods and observations continued for 2 hourly post-work controls. The 1st day of fasting there was no increase in excreted nitrogen during exercise. The 2nd day, there was some increase during exercise, a maximum increase on the 4th day, and, less each succeeding day, until there was no increase on the 8th, 9th and 10th days.