The metabolism of niacytin in the rat. Studies of the excretion of nicotinic acid metabolites

The metabolism of niacytin in the rat. Trigonelline as a major metabolite of niacytin in the urine

“…Animal8 and diet. The animals and diet were similar to those described in the preceding paper (Mason & Kodicek, 1970). The groups of four rats were dosed as follows, each dose containing lmg of free or bound nicotinic acid: group 1, undosed control; group 2, free nicotinic acid; group 3, niacytin; groups 4a and 4b, hydrolysed niacytin.…”

“…The groups of four rats were dosed as follows, each dose containing lmg of free or bound nicotinic acid: group 1, undosed control; group 2, free nicotinic acid; group 3, niacytin; groups 4a and 4b, hydrolysed niacytin. The preliminary experiments described below (see the Results section) refer to urine and faeces samples obtained from rats (undosed and dosed with niacytin) in the experiments described by Mason & Kodicek (1970).…”

“…Animals in group 3 each received 0.5 ml of a solution containing 74.0mg of niacytin/ml, equivalent to 2.0mg of bound nicotinic acid/ml. Niacytin was prepared as described by Mason & Kodicek (1970). Animals in groups 4a and 4b each received 0.5ml of a hydrolysed niacytin solution in which the nicotinic acid present was entirely as the free acid; niacytin (185mg/ml) was hydrolysed in 5M-NaOH at 100°C for 15min, neutralized and made up to final concentration of 74.Omg/ml.…”

“…This hypothesis explains the absence ofbiological activity of niacytin. An endogenous source of urinary trigonelline was also demonstrated.Niacytin, the unavailable form of nicotinic acid in cereals, was shown not to be metabolized via a direct turnover of nicotinic acid in the rat (Mason & Kodicek, 1970). Further, after administration of niacytin little or none of the dose was detected in faeces or urine as tertiary nicotinoyl derivatives, indicating that the substance was not simply excreted unchanged.…”

Nutritional Adequacy, Nutrient Availability and Needs

“…One possibil ity is that some other characteristic of the test foods is stimulating growth s)ightly in the young rats. Mason & Kodicek (1970), working with a concentrate of soluble "bound niacin" from wheat bran, with the free niacin removed by dialysis, found that it too gave a growth response with rats. We made a s imil ar preparat ion and a rat assay gave a value equivalent to an estimated 17% availabil ity of the niacin (Carter & Carpenter, 1982a).…”