EFFECT OF PREDNISOLONE ON THE URINARY-EXCRETION OF NICOTINAMIDE AND ITS METABOLITES IN RATS FED WITH A NIACIN-FREE DIET

Adrenal cortical hormone seems to play an important role in de novo NAD biosynthesis from tryptophan. Therefore, the effects of prednisolone, a synthetic adrenal cortical hormone, on the urinary excretion of nicotinamide and such catabolic metabolites as N1-methylnicotinamide (MNA), N1-methyl-2-pyridone-5-carboxamide (2-Py) and N1-methyl-4-pyridone-3-carboxamide (4-Py) were investigated. Rats fed with a niacin-free diet were intraperitoneally injected with prednisolone (3 mg/rat) three times at 09:00, 13:00 and 17:00 hr on day 0. As a result, the urinary excretion of nicotinamide, MNA, 2-Py and 4-Py was each higher in the prednisolone group than in the physiological saline group (for control) after 1 day; however, each excretion was lower in the prednisolone group than in control group after 3, 4, 5 and 6 days. On around the 7th day, the urinary excretion in the prednisolone group was restored to the control values. The initial rapid increase and subsequent decrease in the urinary excretion of nicotinamide and its metabolites by an injection of prednisolone is considered to be attributable to a respective elevation of the liver tryptophan oxygenase level and the liver aminocarboxymuconate-semialdehyde decarboxylase level. © 1990 by the Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.