Studies of rat liver microsomal diglyceride acyltransferase and cholinephosphotransferase using microsomal-bound substrate: effects of high fructose intake

Abstract

Radiolabeled phosphatidate and diglyceride were prepared bound to rat liver microsomes. These compounds were used as substrates in studies of diglyceride acyltransferase, cholinephosphotransferase, and CTP:phosphatidic acid cytidylyltransferase. Optimum incubation conditions for these reactions in microsomes from normal male rats are described. High fructose diets were fed to rats for 11 days; this resulted in an increased rate of neutral lipid formation from sn-glycerol-3-phosphate by liver microsomal preparations. This was attributed, in part, to a previously reported increase in liver phosphatidate phosphatase activity. The significance of this increase is supported by the finding of a fall in microsomal phosphatidate content and a doubling in microsomal diglyceride. In addition, diglyceride acyltransferase measured with microsomal-bound diglyceride was increased twofold with no equivalent change in cholinephosphotransferase activity. Such a change should result in preferential triglyceride formation from the increased microsomal diglyceride pool. CTP:phosphatidic acid cytidylytransferase activity was depressed by the high fructose diet. These combined alterations would lead to an accelerated hepatic triglyceride formation, a result found in vivo during high fructose feeding. The high fructose diet decreased slightly the total microsomal phospholipid content and markedly depressed phosphatidylethanolamine levels.