LACK OF HORMONAL-STIMULATION OF PYRIDOXINE METABOLISM IN ISOLATED RAT HEPATOCYTES

Isolated hepatocytes obtained from Sprague-Dawley rats (145-175 g) were incubated for 15 min at 30°C in Krebs-Henseleit bicarbonate buffer, pH 7.4, containing 0.5 mm concentration of each of the 20 natural amino acids and either 4.5 or 23 μm [U-14C]pyridoxine. Pyridoxine, pyridoxal, pyridoxal phosphate, and pyridoxic acid separated by an anion-exchange chromatographic technique were quantified using a phosphate analyzer and a liquid scintillation counter. The conversion of [U-14C]pyridoxine to its metabolites was more than doubled by increasing the amount of pyridoxine (4.5 to 23 μm) in the incubation medium. Insulin (10 mU/ml), glucagon (1 nm), or epinephrine (10 μm) did not have any significant effect on the conversion of [14C]-pyridoxine to pyridoxal, pyridoxal phosphate, or pyridoxic acid. Our earlier observations of a large decrease in serum pyridoxal phosphate in the diabetic rat cannot be explained by any direct hormonal effects on pyridoxine metabolism. © 1992.