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Studies in Nicotinic Acid Metabolism

II. The Fate of Nicotinic Acid in Normal and Black Tongue Dogs¹

Department of Biochemistry, Duke University School of Medicine, Durham, North Carolina

A study of the excretion of acid hydrolyzable nicotinic acid derivatives (NA) and trigonelline in dogs, at different levels of nicotinic acid intake, is presented. Trigonelline and nicotinuric acid are the main end products of nicotinic acid metabolism found in dog urine.

The urinary excretion of trigonelline falls to 1.1 to 2.7 mg. per day on a low nicotinic acid diet, and to 0.1 mg. in the black tongue dog.

On the low nicotinic acid diet or in black tongue several 25 mg. doses of nicotinic acid are required before the dog will excrete part of the dose.

On a high nicotinic acid diet (1.1 mg. per kilogram) dogs excrete a total of about 7 mg. of the 12 to 15 mg. they ingest daily. Over 90% of this is in the form of trigonelline.

After saturation with nicotinic acid, doses of 100 mg. of this compound or nicotinamide are completely excreted in the form of trigonelline (75 to 94%) and nicotinuric acid (6 to 25%). The addition of glycine and choline does not influence the proportions excreted as nicotinuric acid or as trigonelline.

Neither trigonelline nor nicotinuric acid can be utilized by the dog.

² Upjohn Fellow in Biochemistry.

Manuscript received 18 August 1941.