QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Patterson, J. I. Articles by Harper, A. E. Search for Related Content PubMed PubMed Citation Articles by Patterson, J. I. Articles by Harper, A. E.

Effect of Tryptophan Intake on Oxidation of [7a-¹⁴C]Tryptophan and Urinary Excretion of N¹-Methylnicotinamide in the Rat¹

Departments of Nutritional Sciences and Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53706

Oxidation of tryptophan and urinary excretion of niacin metabolites were studied in weanling rats fed ad libitum for 12 to 16 days niacin-free and nicotinamide-supplemented (20 mg/kg of diet) diets containing 15% of crystalline amino acids and from 0.04 to 1.0% of L-tryptophan. N¹-methylnicotinamide was measured in urine collected during the last 3 days of the feeding period. After the feeding period, rats were placed in metabolic cages, and each rat was given 4 g (dry weight) of diet containing a tracer dose of DL-[7a-¹⁴C]tryptophan. Expired CO₂ was collected hourly for 10 hours. In both the niacin-free and nicotinamide-supplemented groups, weight gains increased with increasing increments of tryptophan up to about 0.16% L-tryptophan. With more than 0.16% of L-tryptophan, the amount of N¹-methylnicotinamide excreted per day by both groups of rats increased linearly with increasing tryptophan intake, but proportionately less N¹-methylnicotinamide was excreted when the dietary tryptophan level was 1.0%. The amount of tryptophan oxidized per 10 hours increased linearly with increasing dietary tryptophan levels between 0.16 and 1.0%. Therefore, the decline in excretion of N¹-methylnicotinamide with the 1.0% tryptophan level could not be accounted for by increased oxidation. These results suggest that after the tryptophan requirement for growth is met, the amount of tryptophan oxidized and converted to nicotinamide is directly proportional to the level of tryptophan intake up to about 3 times the requirement for growth. The tryptophan requirement of the growing rat fed niacin-free and nitcotinamide-supplemented diets estimated from the inflection points of N¹-methylnicotinamide excretion curves was in good agreement with the requirement of about 100 µmoles/day determined from the growth curve.

KEY WORDS: • amino acid oxidation • tryptophan • niacin • niacin formation from tryptophan

¹ Supported in part by the College of Agricultural and Life Sciences of the University of Wisconsin-Madison, by grant number AM 10748 from the National Institutes of Health, Bethesda, Maryland, and from funds provided by the National Dairy Council, Chicago, Illinois.

² Present address: Department of Home Economics, Cook College, Rutgers University, New Brunswick, NJ 08903.

Manuscript received 24 September 1981.