Excretion of Urea in the Rabbit at Different Age Periods. ∗

Abstract

Urea determinations have been made in many kinds of animals and under various conditions, but the literature apparently does not contain any reference to a relationship of urea excretion in normal rabbits to the age of the animal. This investigation was therefore undertaken to ascertain the daily amount of urea nitrogen excreted in the urine of rabbits from birth to adult condition. Fifty-one rabbits were used, including all ages from fully grown fetuses to adult animals.

Collection of urine. To collect the urine from the fetuses the mother was killed by decapitation, and the abdomen of the fetus after removal from the uterus was opened by an incision. The urine was removed by means of a fine hypodermic needle. The same method was used for collecting urine from the new born rabbits up to the age of 4 days. In these experiments practically no urine was found in the bladders of 8 fetuses and 12 new born rabbits, 2 to 5 minutes after parturition, except for a very small drop occasionally encountered, which was not sufficient to make urea determination by the procedure employed. Dr. Wallin† informs me that he has made similar observations on the absence of urine in the bladder of fetuses or new born rabbits. It is interesting to note that whenever the new born rabbits were permitted to feed, the bladder was seldom, if ever, found to be full. On the other hand, if they were taken away from the mother at birth and starved for from 10 hours to 3 days, the bladder on opening was almost always full of urine.

In one set of experiments animals over 10 days old were kept in metabolism cages, the urine being collected in a beaker placed underneath, and changed every 24 hours.