Effect of Insulin on Plasma Level and Excretion of Vitamin C. ∗

Abstract

In studying the metabolism of vitamin C in normal and depan-creatized dogs, the urinary excretion of the vitamin was found to be strikingly reduced in the diabetic animal. The diets in both groups of animals were totally devoid of vitamin C; dried meat powder was used in place of raw beef. The dogs were kept in individual metabolism cages and the urines were collected by catheter at the start and end of each 24-hour period. Urines voided between catheterizations were collected in dark bottles containing sulphuric acid and hydroxyquinoline to prevent the destruction of the urinary ascorbic acid. Fasting bloods were taken for the determination of the plasma vitamin C. 1 Urinary vitamin C was determined by the method of Evelyn. 2 The depancreatized dogs received insulin twice daily in amounts which allowed a moderate daily excretion of sugar.

The 6 normal dogs excreted an average of 20.6 mg of vitamin C per kg of body weight in 24 hours. The fasting plasma levels of vitamin C varied from 0.55 to 0.94 mg %. The 7 diabetic dogs maintained on insulin excreted on an average only 3.6 mg of vitamin C per kg of body weight in 24 hours. The fasting plasma levels varied from 0.33 to 0.71 mg %.

The influence of injected insulin on the plasma level and excretion of vitamin C was studied in a series of acute experiments in both the normal and depancreatized dog. Control experiments were run on each dog to ascertain the hourly plasma variation and urinary excretion of vitamin C. Over a period of 8 hours the plasma levels of vitamin C in the normal dog varied from 0.58 to 0.66 mg % and the urinary excretion varied from 2.16 to 4.92 mg per hour (Chart 1).