Diuretic effects of the caffeine group

Abstract

The knowledge concerning the diuretic action of caffeine and theobromin has been obtained almost entirely through work on rabbits. It is from this work that the many explanations of how these drugs act in producing diuresis have arisen. The dog was early recognized as being somewhat refractory or uncertain in his response, and consequently but little work has been done on this animal. It has seemed to us however that the dog's urinary function is much more comparable to that of man than is the rabbits, and we have accordingly carried out a series of diuretic experiments using dogs as the experimental animals.

The dogs used were placed on a fixed diet, with a fixed daily intake of water. We have collected and analyzed the urine in twenty-four periods in order to avoid the frequent and unexplained variations which occur in shorter periods. Drugs were withheld until a comparatively constant daily output of urine both in quantity and composition was obtained. Caffeine, theobromin or theobromin sodio-salicylate was then given in dosage varying from 0.05 to 0.2 g. three times a day, for periods of from one to five or more days. They were given with the food and in capsules.

The results may be summarized as follows: With none of these drugs, in the dosage employed have we seen any appreciable increase in the urine output. On the contrary there has been almost invariably a decrease. When the drug is given for one day only, the decrease may occur on that day or the one following. When given for several days the decrease usually continues during the entire period, although in some instances the urine output may return to the normal level on the fourth or fifth day.