Production of a factor which inhibits the mitochondrial enzyme pyruvate dehydrogenase : by exposing H-35 hepatoma cells to dexamethasone prior to treatment with insulin

Treatment of cells with insulin modulates the activity of many cell enzymes. In many cases steroid hormones have the opposite effects on these enzymes. The mechanism for this is unknown. The following thesis details the isolation of a low molecular weight compound which is released after insulin binding to Reuber H-35 cells which increases the activity of the mitochondrial enzyme pyruvate dehydrogenase. Another low molecular weight compound was isolated if these same cells were pretreated with the synthetic steroid dexamethasone prior to treatment with insulin. This compound had the opposite effect on pyruvate dehydrogenase: it decreased the activity. The concentration of insulin and dexamethasone were varied as was the time of treatment. At the conclusion of treatment the compounds were isolated. The effect of these isolates on the activity of pyruvate dehydrogenase was used to quantitate the amount of these compounds produced. It was found that the stimulating compound was produced maximally after ten minutes of treatment with 100 nM insulin. The inhibiting compound was maximal after a ten hour treatment with 1μM dexamethasone. It is concluded that the production of this inhibitor by dexamethasone indicates how steroids might reverse some of the effects of insulin.