Excretion of Insulin by Normal and Pathologic Rabbit Kidney

Abstract

Recently, Jourdonais and one of us 1 demonstrated the presence of insulin in the blood stream for 60 to 90 minutes after the intravenous injection of massive doses of insulin in rabbits. After that period, insulin was not detected in the blood by the procedures used. To determine the fate of at least part of the injected insulin, the present experiments on the renal excretion of this hormone were planned. Moreover, since insulin is readily adsorbed to proteins, we endeavored to determine whether insulin is lost in greater amounts through the pathologic kidney exhibiting proteinuria than through the normal kidney. These preliminary studies will indicate our results to date.

Three rabbits received 200 units of insulin∗ intravenously and one the same amount subcutaneously. Urine specimens (by catheter) were collected before and at regular intervals after the injection of insulin for the next 5 or 6 hours. The bladder was washed with 2 or 3 cc of water after the collection of each urine specimen. Gentle abdominal massage over the bladder area was then employed to insure complete emptying of the bladder. All urines, including the controls, were preserved by the addition of 2 or 3 drops of 1/1000 solution of merthiolate (Lilly). Thirty urine specimens, including 6 controls, were obtained from these 4 rabbits, each of which was injected intravenously into a fasting test rabbit, in most instances within 48 hours of its collection.

Proteinuria was induced in 3 rabbits by the subcutaneous injection of 2 mg per kg of uranium nitrate. The same experimental procedure as outlined above was carried out on the pathologic rabbits. Eighteen urines, including 3 controls, were obtained from these animals; these were injected intravenously into fasting test rabbits.

Table I represents one of the 4 experiments carried out on the excretion of insulin by the normal rabbit kidney, and Table II one of the 3 experiments on the excretion of insulin by the rabbit kidney rendered pathologic with uranium nitrate. These protocols show (1) insulin is not a constituent of the urine of normal rabbits or of the urine excreted by the rabbit kidney rendered pathologic with uranium nitrate, at least in the quantities employed.