The effect of chronic diabetes, induced by streptozotocin, on the activities of some enzymes of glycerolipid synthesis in rat liver

Abstract

1. Rats were injected with a single dose of 35mg of streptozotocin/kg body wt. They exhibited a diabetes that was characterized by glycosuria, polyuria, polydipsia, hyperphagia, hyperglycaemia, increased concentrations of unesterified fatty acids, glycerol and triacylglycerols in the serum and an increased activity of glucose 6-phosphatase in the liver. 2. After 10 weeks the hepatic activities of the microsomal glycerol phosphate acyltransferase, phosphatidate phosphohydrolase, phosphatidate cytidylyltransferase, diacylglycerol acyltransferase, choline phosphotransferase, CDP-diacylglycerol-inositol phosphatidyltransferase and the soluble phosphatidate phosphohydrolase were measured. 3. The only significant changes were an increase in the activity of the soluble phosphatidate phosphohydrolase and a decrease in that of the CDP-diacylglycerolinositol phosphatidyltransferase in the diabetic rats. 4. These results are discussed in relation to the control of glycerolipid synthesis.Diabetes mellitus is characterized by hyperglycaemia, which is often accompanied by glycosuria, and by an increase in the consumption of food and water and in urine output. In severe cases there is ketonaemia, ketonuria and hypertriglyceridaemia. The last is usually caused by an accelerated secretion of very-low-density lipoprotein, and the severity of the hypertriglyceridaemia can be taken as an indication of the adequacy of the control of the diabetes (Nikkila & Kekki, 1973;Nikkila, 1974).In the present study rats were made chronically diabetic by a single injection of streptozotocin. These animals were then used to investigate whether the diabetic state is accompanied by changes in the relative activities of the enzymes responsible for the synthesis ofglycerolipids in the liver. It is hoped that these results will add to our understanding of how glycerolipid synthesis is controlled.