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Oxidized Pyridine Nucleotides in Various Fractions of the Blood and Niacin and Tryptophan Metabolites in the Urine of Women on a Controlled Adequate Dietary¹

Nutrition Research Laboratory, School of Home Economics, and the Experiment Station, Department of Home Economics, Oregon State College, Corvallis

Daily fasting levels of oxidized pyridine nucleotides (expressed as DPN) in whole blood and blood cells and of N¹-methylnicotinamide (N¹MN) in serum were determined fluorometrically for 4 women receiving for 30 days a controlled dietary containing 8.7 mg of niacin and 770 mg of tryptophan. Concomitant 24-hour urinary excretions were analysed for N¹MN, 6-pyridone, niacin, tryptophan and quinolinic acid. Determinations of hematocrit value and urinary nitrogen and creatinine provided additional information.

The group means and ranges for the DPN content of whole blood and red blood cells for the whole period were 34.0 (30.0 to 37.1) and 75.3 (63.4 to 86.8) ug/ml respectively. For the last 23 days of the study, the corresponding values for DPN in white blood cells were 87.9 (82.5 to 94.4) µg/gm and for N¹MN in serum, 0.017 (0.003 to 0.023) ug/ml.

There was little variation in the day to day content of DPN in the red blood cells or whole blood for any of the subjects as evidenced by a mean of 7% for the coefficients of variation for the 30 days. Coefficients of variation of 3 and 4% respectively for the results of the analyses of the control filtrates of these two blood fractions indicated that these were the most reliable fractions to measure. The white blood cell and serum levels showed a greater variation but maintained the trend of individual patterns of concentration found in all fractions.

The means and ranges of the urinary niacin, N¹MN and 6-pyridone were 0.44 (0.36 to 0.54), 5.8 (4.5 to 7.3) and 7.3 (4.9 to 12.0) mg/day respectively. Corresponding values for free and total tryptophan and for quinolinic acid were 12.9] (10.9 to 15.1), 25.4 (21.3 to 32.0) and 4.9 (3.7 to 6.4) mg/day.

For all subjects a period of adjustment of up to 16 days was indicated by the change in levels of serum N¹MN, and urinary N¹MN and 6-pyridone.

Two subjects were alike in a tendency to negative nitrogen balance, negative niacin balance and a ratio of 6-pyridone to N¹MN exceeding one.

² In this paper, the data on blood are taken from the thesis presented by Nina H. Morley to the Graduate School of Oregon State College in partial fulfillment of the requirements for the Ph.D. degree, June 1957; Present address: Dept. of Opthalmology, Banting Institute, Toronto, Canada.

Manuscript received 5 July 1957.