Abstract

Male and female Sprague-Dawley rats were maintained on synthetic diets for three weeks. One diet was deficient in thiamine and the other was a high thiamine (HT) diet that supplied an average daily intake of 2.0 mg of thiamine to each animal. Rats receiving the HT diet showed significant reductions in aniline, zoxazolamine and aminopyrine metabolic rates in vitro, whereas hexobarbital metabolic rate was not significantly altered. A reduction in hepatic microsomal cytochrome b₅ and cytochrome P-450 contents without a reduction in microsomal protein content was evident in rats fed the HT diet. As further evidence for this effect being in the microsomal fraction, increasing reduced nicotinamide adenine dinucleotide phosphate levels in the incubation mixtures failed to increase metabolic rates; furthermore, the 105,000 x g liver supernatant from rats fed the thiamine-deficient diet did not enhance the metabolic rate of microsomes from rats fed the HT diet; nor did the supernatant from animals fed the HT diet depress the metabolic rate of microsomes from the deficient group. Reduced nicotinamide adenine dinucleotide phosphate-cytochrome c reductase activity of microsomes from rats fed the HT diet was depressed.