The effect of fasting and refeeding on the composition and synthesis of triacylglycerols, phosphatidylcholines, and phosphatidylethanolamines in rat liver

Abstract

Refeeding a high-sucrose, fat-free diet to fasted rats caused drastic alterations in the fatty acid composition of hepatic diacylglycerols, triacylglycerols, and phosphatidylcholines. However, the fatty acid profile of phosphatidylethanolamines did not change significantly. These results suggest that the fatty acid composition of diacylglycerols may influence the distribution of diacylglycerols among triacy@ycerols, phosphatidylcholines, and phosphatidylethanolamines. Fasting and refeeding also affected the activities in vitro of a number of enzymes responsible for the formation of triacylglycerols, phosphatidylcholines, and phosphatidylethanolamines.The activity of hepatic phosphatidate phosphatase increased fourfold upon refeeding. However, fasting the rats did not affect the activity of this enzyme despite the reduced triacylglycerol synthesis in the fasted liver in wivo. Fasting and refeeding induced alterations in the activities of diacylglycerol acyltransferase, cholinephosphotransferase, and ethanolaminephosphotransferase which correlated reasonably well with the changes observed in the synthesis of triacylglycerols, phosphatidylcholines, and phosphatidylethanolamines in vivo, although the changes in diacylglycerol acyltransferase were too moderate. The changes in the activity of cholinephosphate cytidylyltransferase, which is suggested to catalyze the rate-limiting step in the formation of CDP-choline, ran parallel with the alterations in the synthesis of phosphatidylcholines in vivo. No such correlation was found between the activity of ethanolaminephosphate cytidylyltransferase and the rate of phosphatidylethanolamine synthesis. The present results indicate that the synthesis of triacylglycerols, phosphatidylcholines, and phosphatidylethanolamines is controlled by the availability of the various substrates as well as by the activities of several enzymes involved in these processes.

Effects of vasopressin on the synthesis of phosphatidylethanolamines and phosphatidylcholines by isolated rat hepatocytes

“…Table I shows that the activity of ethanolaminephosphate cytidylyltransferase was high compared to the activity of ethanolamine kinase. This was also reported by Groener et al [22] and by Schneider and Vance [23]. On the other hand, it was shown that the activity of cholinephosphate cytidylyltransferase in rat liver is much lower than the activity of choline kinase W&'l.…”

Abnormal phosphomonoester signals in 31P MR spectra from patients with hepatic lymphoma. A possible marker of liver infiltration and response to chemotherapy

“…207-253). In particular, CDP-choline synthesis appears to be the rate limiting step in the synthesis of phosphatidylcholine, whereas the incorporation of '4C-ethanolamine into phospholipids is not directly related to the specific activities of the enzymes involved (Groener et al, 1979). The ethanolamine pathway (Figure 7) may therefore also be regulated by the supply of substrates such as CTP or suitable diacyl glycerols (Sundler & Akesson, 1975a).…”

Control of the CDPethanolamine pathway in mammalian cells: effect of CTP:phosphoethanolamine cytidylyltransferase overexpression and the amount of intracellular diacylglycerol

“…Samples were collected, 48 h after transfection, to confirm expression of hCEPT1 using the cholinephosphotransferase activity assay. The activity was determined in the presence of exogenous DAG, as described by Groener et al [27]. At the same time point, the rate of PtdEtn synthesis was determined as described in the Incorporation of radioactive precursors into PtdEtn and PtdCho subsection.…”