What is urobilin?

Urobilin

Q. What is urobilin?

A. Urobilin is produced by decomposition of the pigment of the bile. It is not found at all in normal urine. According to Muller the urobilin found in the intestine is largely absorbed and again excreted in the bile. It is only when the amount of urobilin is greater than the liver can thus dispose of that it is absorbed into the blood and appears in the urine. Lauder-Brunton some years ago observed that the bile from a biliary fistula lacks the bitter taste which is characteristic of vomited bile. It appears then that there is really some truth in the old medical theory that the bile becomes thick or concen­trated and that a person whose bile is in this con­dition may be benefited by getting rid of a large amount of the bile by vomiting or purging. This perhaps explains the temporary benefit derived from the use of calomel which so long main­tained the popularity of this harmful drug. The calomel by increasing the action of the bowels carries off a considerable quantity of bile, thus getting rid of the accumulated urobilin and other poisons which the bile contains and so relieves the patient of the unpleasant effects produced by this powerful toxic substance. Bouchard showed, many years ago, that the bile pigment is one of the most poisonous substances produced in the body. Macfadyn and others have ,shown that urobilin is rarely found in the small intestine, be­ing absorbed very quickly and completely after entering the intestine from the liver. Its pro­duction is confined to the large intestine by the putrefactive processes taking place there. It can readily be seen that in cases of incompetency of the ileocolic valve permitting the entrance of putrifying materials into the small intestine, the poisonous effects resulting from theabsorption of urobilin must be greatly increased.

In the new born there is no putrefaction in the intestines and hence there is no urobilin found in the urine.