Histochemical study on riboflavin.

Abstract

The authors improved the histochemical method for riboflavin, devised a phosphatase method, and established the principle of separate observation of the three forms of riboflavin. Using this method, histological distribution of riboflavin in normal and CCl4-poisoned rats was observed. Furthermore, the fate of the three forms of riboflavin after loading with riboflavin (FR), flavin mononucleotide (FMN) and flavin-adenine dinucleotide (FAD) was studied with the following results.1. To extract riboflavin histochemically, benzyl alcohol treatment is the most suitable.2. For converting the esterified riboflavin into the free form, the enzymatic method using phosphatase is the most adequate.3. Riboflavin occurs widely in the animal body, mostly in the esterified form, especially FAD. However, the distribution varies according to the organs.4. Riboflavin is absorbed largely from the small intestine, whereby it is phosphorylated into FMN in the mucous epithelia, and is transferred to the liver to be converted into FAD.5. After oral administration of free vitamin, the rise of the levels of each component of the vitamin is observed in the body. After loading with FMN, the levels of both FMN and FAD is increased, whereas after loading with FAD, only a slight amount of FAD was observed.6. After injection of FR, increase of FR is observed without any change of FMN and FAD. After injection of FMN, both FMN and FAD were increased in the body but after injection of FAD, a slight amount of FR was increased in the mucous layer of intestinal mucosa, and in other tissues FAD was increased.7. In the CCl4-poisoned rats, decrease of the esterified form of the vitamin was generally seen. After loading with the vitamin, depression of absorption and phosphorylation of the vitamin was noted.