Abstract
The feeding on a diet containing thyroxine to rats significantly increased the conversion ratio of tryptophan to niacin, while, the feeding on a diet containing estrone decreased. The feeding on a diet containing progesterone or testosterone did not affect the conversion ratio. An intraperitoneal injection of adrenaline, alloxan, or streptozotocin caused the decreased conversion ratio. The intraperitoneal injection of prednisolone, a synthetic adrenal cortical hormone, increased the conversion ratio after 1 day ; however, the conversion ratio was lower in the prednisolone group than in control group after 3, 4, 5 and 6 days. On around 7th day, the conversion ratio was restored to the control values. The target of these hormones, by which the conversion ratio was affected, was the activity of liver aminocarboxymuconate-semialdehyde decarboxylase. Thus, the metabolism of tryptophan to niacin is found to be regulated and controlled by the activity of aminocarboxymuconate-semialdehyde decarboxylase via thyroid gland, adrenal, pancreas, and ovary hormones.
