The effect of dietary carbohydrate and fat on the activities of some enzymes responsible for glycerolipid synthesis in rat liver

Abstract

1. Male rats were fed for 14 days on diets containing (by wt.) 53% of starch, or on diets in which 20% of the starch was replaced by sucrose, corn oil or lard. 2. The hepatic activities of the microsomal glycerol phosphate acyltransferase, dihydroxyacetone phosphate acyltransferase, phosphatidate cytidylyltransferase, diacylglycerol acyltransferase and choline phosphotransferase, and of the soluble phosphatidate phosphohydrolase, were measured. 3. The soluble phosphatidate phosphohydrolase activity was higher in those rats fed on lard than in those fed on the starch diet. Choline phosphotransferase activity was higher in the rats fed on corn oil than in those fed on the starch diet. 4. The rate of hepatic glycerolipid synthesis was measured in vivo 1 min after injection of [1,3-3H]glycerol and [1-14C]palmitate into the portal veins. 5. The relative rate of phosphatidylcholine synthesis in vivo was increased after feeding with corn oil and the higher specific activity of choline phosphotransferase may contribute to this result. The equivalent rate of triacylglycerol synthesis was increased by feeding with lard rather than corn oil, and the increased activity of phosphatidate phosphohydrolase may partly explain this. The latter changes probably contribute to the increased concentration of triacylglycerol which other authors have observed in the livers and sera of animals fed on saturated and monounsaturated fats.

The effects of cortisol, corticotropin and thyroxine on the synthesis of glycerolipids and on the phosphatidate phosphohydrolase activity in rat liver

“…radioactivity 58piCi/,umol) and 188 uM-[1,3-3H]glycerol (sp. radioactivity 1638,pCi/pmol) (Brindley et al, 1976;Glenny et al, 1978).…”

“…The experiments were carried out to provide evidence that injecting the hormones caused changes in the hepatic glycerolipid metabolism of the rats described in Table 1. This approach has already been used to study the effects of dietary modification and the effects of drugs (Brindley et al, 1976;Savolainen, 1977;Glenny et al, 1978).…”

Lipid deprivation increases surfactant phosphatidylcholine synthesis via a sterol-sensitive regulatory element within the CTP:phosphocholine cytidylyltransferase promoter

“…To investigate these mechanisms, we focused on the PtdCho biosynthetic pathway, because two enzymes in this pathway, cholinephosphotransferase and CCT, are lipid regulated. Interestingly, both enzymes are post-translationally activated by fatty acids, and thus lipid-deprivation would be expected to lead to enzyme inhibition with an overall decrease in surfactant PtdCho content explaining prior data [6][7][8]43]. Indeed, this was observed with cholinephosphotransferase ; however, CCT activity was unexpectedly stimulated after lipid deprivation as a consequence of increased mRNA synthesis [21].…”