RESUMO
To further define the mechanism of interaction among phenytoin, folates and cobalamins in rats, we studied the effect of phenytoin (60 mg/(kg.day)) with or without folic acid supplementation and with or without cobalamin deficiency, as well as the effect of supplementing with folic acid (200 mg/kg diet) with or without a cobalamin deficiency, on the tissue concentrations of folates and phenytoin (determined respectively by HPLC and fluorescence polarization). The major tissues (liver, intestinal mucosae, blood and brain) were studied. A folic acid overload (estimated at about 2 mg/day) increased folate levels in the liver, the intestinal mucosae and blood, while there was no effect on cerebral levels. Phenytoin had no significant effect on folate tissue concentration. The major finding was that a folic acid overload caused a considerable decrease in the hepatic and cerebral concentrations of phenytoin. This decrease could be responsible for the increased frequency of epileptic fits in patients treated with this anticonvulsant drug when combined with a folic acid supplement. Concentration changes of the drug in cobalamin-replete or -deficient rats, with or without folic acid supplementation, suggest that the interaction between the anticonvulsant and the two vitamins (folates and cobalamins) occurs at the level of transmethylation reactions.
Assuntos
Ácido Fólico/metabolismo , Ácido Fólico/farmacologia , Fenitoína/farmacologia , Deficiência de Vitamina B 12/metabolismo , Animais , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Cromatografia Líquida de Alta Pressão , Polarização de Fluorescência , Ácido Fólico/sangue , Mucosa Intestinal/efeitos dos fármacos , Mucosa Intestinal/metabolismo , Fígado/efeitos dos fármacos , Fígado/metabolismo , Masculino , Ácido Metilmalônico/urina , Ratos , Ratos Sprague-DawleyRESUMO
A technique for the extraction, purification and concentration of folates, followed by high performance liquid chromatography assay with fluorometric detection of the three principal derivatives (tetrahydrofolic, 5-methyl-tetrahydrofolic and formyl-tetrahydrofolic acids) has been applied to the determination of tissue folates in rats. The levels found are compared to those of the microbiological assay using Lactobacillus casei. When rats were fed a diet containing 1 mg of folic acid per kg of food, levels in the intestinal mucosae, liver, whole blood and brain were 0.59, 14.87, 0.28 and 0.83 nmol/g of tissue. An exogenous supply of 200 mg of folic acid/kg of food significantly increased folate levels in all tissues studied, except for the brain: 1.51, 28.93, 0.52 and 0.99 nmol/g, respectively in the above four tissues. The separation of the various derivatives and a variable supply of folic acid have enabled the conversions of these metabolites to be studied.
Assuntos
Dieta , Ácido Fólico/farmacocinética , Animais , Encéfalo/metabolismo , Cromatografia Líquida de Alta Pressão , Fluorometria , Ácido Fólico/sangue , Mucosa Intestinal/metabolismo , Fígado/metabolismo , Masculino , Ratos , Distribuição Tecidual/fisiologiaRESUMO
The native fluorescence of the main biological derivatives of folic acid is maximal at acidic pH. The intensities obtained with 5-methyltetrahydrofolic acid, tetrahydrofolic acid, and formyltetrahydrofolic acid are in the ratio 10/5/1. After separating the metabolites by reversed phase high-performance liquid chromatography, the fluorometric detection limit varied between 0.4 and 20 pmol per injection. Rat liver extract (about 2 g/50 ml of 1% ascorbate solution) could be analyzed after incubation at 37 degrees C overnight, deproteinizing with acetone, and purification and concentration in an ion exchange column. The concentrations obtained varied from 1.27 to 7.96 nmol/g depending on the derivative. Recovery varied from 89 to 113%.
