Effect of inhibition of fatty acid oxidation on neonatal liver carnitine content

Liver carnitine metabolism after partial hepatectomy in the rat. Effects of nutritional status and inhibition of carnitine palmitoyltransferase

This study examined the effects of partial hepatectomy on hepatic carnitine and acylcarnitine concentrations in fed or 24 h-starved partially hepatectomized (PH) or sham-operated (SO) rats at 1 or 4 days after surgery. The ratio of free to esterified carnitine was low in fed PH rats at day 1: the low ratio was increased to the SO value when mitochondrial fat oxidation was inhibited by 2-tetradecylglycidate. Starvation (24 h) increased plasma [non-esterified fatty acid] in PH or SO rats, the increases being greater at day 1 than at day 4. Hepatic [long-chain acylcarnitine] were also increased. These latter increases were a consequence of increased mitochondrial fat oxidation since they were not observed in PH or SO rats treated with 2-tetradecylglycidate. Whereas the starvation-induced increase in long-chain acylcarnitine was associated with increased [ketone body] in livers of SO rats at both day 1 and day 4 after surgery, [ketone body] was inappropriately low for the steady-state long-chain [acylcarnitine] in livers of PH rats at the first post-operative day. This was not a consequence of a decrease in [total carnitine] in the liver. The results are discussed with reference to the role of the liver in determining the relative proportions of the fat fuels available for extrahepatic tissues and the effects of liver cell proliferation on hepatic triacylglycerol metabolism.

Metabolic changes in fed rats caused by chronic administration of ethyl 2[5(4-chlorophenyl)pentyl]oxirane-2-carboxylate, a new hypoglycaemic compound

Ethyl 2[5(4-chlorophenyl)pentyl]oxirane-2-carboxylate (POCA) is strongly hypoglycaemic in fasted normal and diabetic rats [H. P. O. Wolf, K. Eistetter and G. Ludwig, Diabetologia 22, 456 (1982)]. POCA was fed for 12 weeks to rats on a standard low-fat (3%) diet at levels of 0.05% and 0.2% to give daily intakes of about 50 and 200 mg/per kg body-wt respectively. This is much more than effective hypoglycaemic doses in fasted rats (5-10 mg/kg body-wt). The animals appeared healthy but they had slightly decreased rates of weight gain compared with the controls. POCA caused a 15% increase in the weight of the myocardium and accumulation of lipid in the liver. Chronic administration of POCA did not cause any large changes in water-soluble blood metabolite concentrations, although VLDL-triacylglycerol and both VLDL and HDL cholesterol concentrations were lowered. There were only small changes in some metabolites of the glycolytic and gluconeogenic pathways and the citrate cycle in liver and skeletal muscle. ATP concentrations were maintained in all groups. There were 2- to 3-fold increases in the total content of CoA and of carnitine and their acylated forms. POCA-feeding caused small decreases in LPL activities in heart and had variable effects in adipose tissue. POCA was also fed to a few rats on a high fat (30%) diet for 4 weeks. Only small changes in blood, liver and muscle metabolite concentrations were found, except for large increases in the liver CoA and carnitine contents. It was concluded that POCA does not cause large perturbations of glucose homeostasis, or acute toxic effects, during 12 weeks administration to normal animals at high dose levels. The very-long term importance of accumulation of lipid in liver; increase in myocardial weight; and also of hepatic peroxisomal proliferation [A. J. Bone, H. S. A. Sherratt, D. M. Turnbull and H. Osmundsen, Biochem. biophys. Res. Commun. 104, 708 (1982)] cannot yet be determined. The possible use of POCA and related compounds in the chemotherapy of diabetes merits further investigation.

Metabolism of branched-chain keto acids in neonatal rat liver perfusions

The ability of the neonatal rat to oxidize the branched-chain amino acids leucine and valine and their corresponding keto acids was evaluated. In vivo, about 20% of orally administered labeled amino or keto acids were oxidized in 6 h, after which time little further oxidation occurred. In perfused neonatal liver the amino acids were oxidized at only 5-10% the rate of the keto acids. The oxidation of the keto acids showed a saturable dependence on concentration. The decarboxylation of ketoisocaproate (KIC) had a maximal rate of 40.1 +/- 1.6 mumol/h/g liver with an apparent Km of 0.27 +/- 0.03 mM, and decarboxylation of ketoisovalerate (KIV) had a maximal rate of 37.9 +/- 1.9 mumol/h/g liver and an apparent Km of 0.28 +/- 0.04 mM. KIC was ketogenic, producing mainly acetoacetate at a maximal rate of 44.5 +/- 1.6 mumol/h/g liver with an apparent Km of 0.27 +/- 0.03 mM. On the other hand, KIV was not gluconeogenic, although the perfused neonatal liver was able to produce glucose from lactate. During liver perfusion, KIV did not produce measurable quantities of either propionic or beta-aminoisobutyric acids, which are possible end products of KIV metabolism. Decanoic acid inhibited the decarboxylation of both keto acids to the same extent with a maximal effect at 0.4 mM fatty acid. At saturating levels, KIC was less ketogenic than decanoate. Inhibition of endogenous fatty acid oxidation by 2-tetradecylglycidic acid had no effect on keto acid oxidation. These data suggest that branched-chain amino acids derived from milk proteins are probably not quantitatively significant sources of either ketone bodies or glucose in the neonatal rat.