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THE EFFECT OF VITAMIN B 12 AND BIOTIN ON THE METABOLISM OF VITAMIN B 12 IN BIOTIN-DEFICIENT RATS.

ABSTRACT: 1. The effect of the administration of vitamin B(12) and biotin on the metabolic pattern of vitamin B(12) in biotin-deficient rats was studied. 2. No significant changes in the absorption and excretion of orally administered [(58)Co]vitamin B(12) were noted either in vitamin B(12)-treated and or in biotin-fed rats. A significant decrease of the uptake of orally given [(58)Co]vitamin B(12) was observed in the liver and kidneys of biotin-treated rats, whereas an increase of uptake in the kidneys of vitamin B(12)-treated rats was noted as compared with biotin-deficient animals. 3. No significant difference in the excretion of radioactivity was noted between biotin deficient and biotin-fed rats when [(58)Co]vitamin B(12) was administered by injection. A small decrease was observed in vitamin B(12)-treated rats. The retention of injected [(58)Co]vitamin B(12) by major organs of biotin-treated rats was lower than that of biotin-deficient rats. A lower content of [(58)Co]vitamin B(12) was also detected in the organs, with the exception of the kidneys, of vitamin B(12)-treated rats. 4. These results are discussed in terms of an interrelationship between biotin and vitamin B(12).

SUBMITTER: PUDDU P

PROVIDER: S-EPMC1206903 | biostudies-other | 1965 Jul

REPOSITORIES: biostudies-other

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Project description:The effect of 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] on 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] metabolism was examined in rats fed on a low-calcium diet. These rats exhibit hypocalcaemia, high urinary cyclic AMP excretion, a markedly elevated serum 1,25(OH)2D concentration and low serum concentrations of both 24,25(OH)2D and 25(OH)D. When the rats are treated orally with 1, 5 or 10 micrograms of 24,25(OH)2D3/100 g every day, there is a dramatic decrease in serum 1,25(OH)2D concentration in a dose-dependent manner concomitant with an increase in serum 24,25(OH)2D concentration. Serum calcium concentration and urinary cyclic AMP excretion are not significantly affected by the 24,25(OH)2D3 treatment, which suggests that parathyroid function is not affected by the 24,25(OH)2D3 treatment. The 25(OH)D3 1 alpha-hydroxylase activity measured in kidney homogenates is markedly elevated in rats on a low-calcium diet but is not affected by any doses of 24,25(OH)2D3. In contrast, recovery of intravenously injected [3H]1,25(OH)2D3 in the serum is decreased in 24,25(OH)2D3-treated rats. Furthermore, when [3H]1,25(OH)2D3 is incubated in vitro with kidney or intestinal homogenates of 24,25(OH)2D3-treated rats there is a decrease in the recovery of radioactivity in the total lipid extract as well as in the 1,25(OH)2D3 fraction along with an increase in the recovery of radioactivity in the water-soluble phase. These results are consistent with the possibility that 24,25(OH)2D3 has an effect on 1,25(OH)2D3 metabolism, namely that of enhancing the degradation of 1,25(OH)2D3. However, because a considerable proportion of the injected 24,25(OH)2D3 is expected to be converted into 1,24,25(OH)3D3 by renal 1 alpha-hydroxylase in 24,25(OH)2D3-treated rats, at least a part of the decrease in serum 1,25(OH)2D concentration may be due to a competitive inhibition by 24,25(OH)2D3 of the synthesis of 1,25(OH)2D3 from 25(OH)D3. Thus the physiological importance of the role of 24,25(OH)2D3 in regulating the serum 1,25(OH)2D concentration as well as the mechanism and metabolic pathway of degradation of 1,25(OH)2D3 remain to be clarified.

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THE EFFECT OF VITAMIN B 12 AND BIOTIN ON THE METABOLISM OF VITAMIN B 12 IN BIOTIN-DEFICIENT RATS.

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