Murray Heimberg

Increased arachidonate in lipids after administration to man: Effects on prostaglandin biosynthesis

Ethyl arachidonate was administered orally to 4 healthy male volunteers in a dose of 6 gm daily for a 2 to 3 wk period after a 1O‐day control period. The increased intake of this precursor of the dienoic prostaglandins resulted in significant increases in the relative and absolute amount of arachidonate in plasma triglycerides, phospholipids, and cholesteryl esters. Similar changes in lipid composition were noted in platelets. The excretion of 7 α‐hydroxy‐5, 11‐diketotetranorprostane‐1 ,16‐dioic acid, the major urinary metabolite of E prostaglandins in man, was increased by an average of 47% in 3 of the 4 volunteers. Platelet reactivity was assessed by determining the threshold concentration of adenosine diphosphate (ADP) necessary to induce secondary, irreversible aggregation of platelet‐rich plasma. This threshold concentration dropped significantly in all volunteers (10% to 60% of control values). It is concluded that the biosynthesis and function of prostaglandins can be augmented in man by oral administration of an esterified precursor fatty acid.

Hepatic lipid metabolism in experimental diabetes: I. release and uptake of triglycerides by perfused livers from normal and alloxan-diabetic rats

Abstract The uptake of nonesterified fatty acids was accelerated and the net release of triglyceride by the isolated perfused rat liver was depressed in alloxan diabetes. Triglyceride release by livers from either normal or diabetic rats was proportional to the palmitate presented to the liver; triglyceride release, however, was depressed in livers from diabetic rats at all concentrations of perfusate fatty acid. Uptake of triglyceride from chylomicra was more rapid by livers from diabetic animals than by livers from normal fed rats. Ketone-body formation and urea production were both accelerated by diabetes and restored to normal levels by treatment with insulin of the animal from which the liver was obtained. Ketone-body output remained constant regardless of the quantity of palmitate added to the perfusion medium. Since the uptake by liver of triglycerides from chylomicra, or from a neutral fat emulsion as reported previously, was accelerated in alloxan diabetes, it was of interest to compare the rates of disappearance of a neutral fat emulsion from the blood stream of normal or diabetic rats. It was observed that the disappearance of neutral fat from the plasma of diabetic rats was delayed considerably in comparison to the normal. Insulin therapy of the animals, moreover, increased the rate of disappearance of esterified fatty acid from the blood. The uptake and release of triglyceride by the isolated perfused rat liver were discussed with reference to a mechanism for the occurrence of fatty liver and hyperlipemia in experimental diabetes.

Effects of several common long chain fatty acids on the properties and lipid composition of the very low density lipoprotein secreted by the perfused rat liver

1. Livers from normal fed male rats were perfused in vitro with a bloodless medium which contained intially 3% bovine serum albumin and 100 mg% glucose. Albumin alone, or myristate (14 : 0), palmitate (16 : 0), palmitoleate (16 : 1), stearate (18 : 0), oleate (18 : 1), or linoleate (18:2) was infused at a constant rate (496 mumol/4 h), as a complex with albumin, during the experiment. 2. The very low density lipoprotein secreted by the liver after infusion of unsaturated fatty acids (16 : 1, 18 :1, 18 : 2) has a faster rate-zonal mobility in the ultracentrifuge and is, therefore, probably a larger particle with fewer moles of phospholipid and cholesterol relative to triacyglycerol (triacyglycerol/phospholipids/cholesterol = 100/25.1/16.4) than the very low density lipoproteins produced after infusion of saturated (14 : 0, 16 : 0, 18 : 0) fatty acids (triacyglycerol/phospholipids/cholesterol = 100/30.1/19.1). The molar ratio of phosphoipids/cholesterol of the very low density lipoprotein was similar regardless of which fatty acid was infused. The predominant fatty acid of the very low density lipoprotein or hepatic triacyglycerol, in all cases, was the infused acid. 3. We conclude that free fatty acid regulates the quantity and proportions of triacyglycerol, phospholipids, and cholesterol secreted by the liver in the very low density lipoprotein, and therefore, may secondarily influence concentrations of lipids in the very low density lipoprotein and other plasma lipoproteins circulating in vivo.

Enrichment of rat tissue lipids with fatty acids that are prostaglandin precursors

The effects of supplementation of a complete diet with ethyl arachidonate and with ethyl dihomo-gamma-linolenate (20 : 3Omega6) on the fatty acid composition of plasma and tissue lipid classes were studied in normal rats. 2. These prostaglandin precursors were incorporated in varying degrees into all lipid classes of the tissues that were investigated. The largest elevations were seen in plasma and tissue triacylglycerols. Significant increases were also observed in phospholipids, cholesteryl esters and the free fatty acid fraction. 3. Following the feeding of the ester of 20 : 3Omega6, arachiodonate levels also rose in the lipids of some tissues. In others, such as the renal medulla and platelets, and increase in 20 : 3Omega6 content occurred without a rise in 20 : 4. 4. Platelet aggregation is known to be stimulated by 20 : 4 (via active metabolites), but not by 20 : 3Omega6. The ability to modify 20 : 3Omega6 levels selectively in certain tissues is of interest in light of such pharmacologic differences from 20 : 4.

Cholesterol is required for the secretion of the very-low-density lipoprotein: in vivo studies.

Rats were fed for 1 week with a standard chow diet, a diet supplemented with lovastatin (0.1%), or a diet supplemented with both lovastatin and cholesterol (0.1/0.1%), to study effects of depletion of a putative hepatic metabolic pool of cholesterol on secretion of the very-low-density lipoprotein (VLDL) in the intact animal. Triton WR-1339 (50 mg/100 g body wt.) or the 0.9% NaCl vehicle alone was given intravenously via a sacral vein. Treatment with lovastatin decreased the secretion of all plasma VLDL lipids, the average decrease after 2 h for VLDL triacylglycerol, phospholipid, cholesterol and cholesteryl ester being 45%. When both lovastatin and cholesterol were included in the diet, the secretion of VLDL triacylglycerol and phospholipid was similar to that of control animals, while secretion of VLDL cholesterol and cholesteryl ester was increased. Treatment with lovastatin reduced the hepatic concentration of cholesteryl esters 42% without affecting free cholesterol. In separate experiments, in vivo synthesis of cholesterol was determined 1 h after intraperitoneal administration of 3H2O. Incorporation into hepatic and plasma free cholesterol and cholesteryl esters was greater in the rats fed lovastatin than in control animals, concurrent with decreased VLDL secretion. The metabolism of VLDL was determined in vivo by intravenous administration of 125I-VLDL. The fractional clearance rates of 125I-VLDL from the plasma were similar among the three experimental groups. Synthesis of hepatic triacylglycerol from [1-14C]oleate in vivo was similar in all treatment groups; incorporation into plasma triacylglycerol was reduced with lovastatin treatment and reversed partially by inclusion of 0.1% cholesterol in the lovastatin diet. Plasma concentrations of triacylglycerol followed patterns of incorporation of [1-14C]oleate. Triacylglycerol concentration in the liver increased when cholesterol was included in the diet. In companion experiments, incorporation of [1-14C]oleate into perfusate triacylglycerol in vitro was reduced with perfused livers from lovastatin-treated animals. In these experiments, oxidation of fatty acid into CO2 and perchloric acid-soluble counts was not affected by lovastatin, added either to the diet or to the perfusate in vitro. It appears, therefore, that lovastatin does not affect triacylglycerol synthesis or fatty acid oxidation, which per se might reduce formation and secretion of VLDL. These data, therefore, strengthen the hypothesis that reduced availability of cholesterol in a putative hepatic metabolic pool, required for secretion and transport of triacylglycerol in the VLDL, is a factor contributing to decreased secretion of the VLDL.

The effects of aliphatic halogenated hydrocarbons on hepatic drug metabolism

Abstract Pretreatment of rats with CCl 4 prolonged the sleeping times evoked by hexobarbital. The metabolism of hexobarbital by the isolated perfused rat liver was reduced after intoxication with CCl 4 and may have been responsible, in part, for the enhanced action of the barbiturate. Poisoning with CCl 4 impaired the oxidation of hexobarbital and aminopyrine as well as the reduction of p -nitrobenzoic acid by liver microsomes. The activity of the drug-metabolizing enzymes declined to about 10 per cent of normal within 8 hr and remained at low levels 24 hr after the administration of CCl 4 . The return of enzyme activity to normal levels started coincident with the disappearance of CCl 4 from the liver and required about 8 days for completion. In contrast to the striking toxicity of carbon tetrachloride, drug metabolism was not reduced after the administration of methylene chloride, and chloroform evoked only a moderate impairment of aminopyrine demethylation.

Sexual influences on hepatic secretion of triglyceride.

Abstract The output of triglyceride by isolated perfused livers from female rats exceeds that by livers removed from male animals. Ovariectomy reduced the secretion of triglyceride by livers from female rats; administration of estrogen to the ovariectomized animals tended to return output toward control levels. It may be suggested therefore, that hepatic output of triglyceride can be regulated by gonadal or gonadotrophic hormones.

Stimulation of hepatic cholesterol biosynthesis by oleic acid

Livers from normal fed male rats were perfused in vitro with an erythrocyte-free, bloodless medium containing serum albumin (3%), and glucose (100 mg %). Oleic acid (663 μmoles) bound to albumin, or albumin alone, was infused at a constant rate. Biosynthesis of cholesterol was evaluated by incorporation of radioactivity from 3H2O. Oleic acid stimulated output of cholesterol (1.60 ± 0.08 SEM vs 1.18 ± 0.04 μmoles/g) but did not change the concentration of cholesterol in the liver or hepatic microsomes. Incorporation of 3H into cholesterol was stimulated by oleate; dpm per μmole cholesterol/dpm per μg atom H was 3.94 ± 0.33, 3.46 ± 0.32, and 4.46 ± 0.37 in the total cholesterol of liver, perfusate, and microsomes, respectively, when oleate was infused. Corresponding values when oleate was not infused were 1.71 ± 0.23, 1.62 ± 0.20, and 2.09 ± 0.26, respectively (P<0.001 in all cases). It is suggested that the stimulation of biosynthesis of cholesterol by oleate results from the obligatory requirement of cholesterol, as a moiety of the very low density lipoprotein, for the secretion of triglyceride by the liver.

The effect of tetracycline on the hepatic secretion of triglyceride

Abstract The results of previous studies which employed indirect techniques suggested that tetracycline induced a fatty liver in rats by inhibition of the hepatic secretion of triglyceride. The present study examines this concept directly by observation of the effect of tetracycline hydrochloride (100 mg/kg) given in vivo on the subsequently isolated perfused rat liver. This dose of tetracycline produced a 67% increase in hepatic triglyceride content in 3 h in vivo. The secretion of triglyceride by livers removed at 3 h from such animals and perfused in vitro was diminished in comparison with livers from control rats (1.6 μmoles/g per 4 h vs 3.4 μmoles/g per 4 h, P

Hepatic lipid metabolism in experimental diabetes: II. Incorporation of [1-14C]palmitate into lipids of the liver and of the d < 1.020 perfusate lipoproteins

Abstract Livers from normal rats, from rats treated 48 h before use with alloxan, and from alloxan-diabetic animals treated with insulin, were perfused in vitro with a medium containing [1- 14 C]palmitic acid. 1. 1. It was observed under our experimental conditions that hepatic release of triglyceride, phospholipid, and cholesterol into the d 2. 2. During these perfusions of livers from diabetic animals with small loads of palmitic acid, hepatic triglyceride concentration was diminished, whereas it appeared to be unchanged in livers from normal rats. 3. 3. Incorporation of 14 C into triglycerides and phospholipids of the d 14 C and the specific activity of liver phospholipid was depressed. Although the incorporation of 14 C into hepatic triglyceride did not appear to be depressed in these experiments as a result of the alloxan diabetes, we can not say that rates of esterification of non-esterified fatty acid to triglyceride were normal; this reservation is necessary since these data were obtained at the termination of the perfusion experiment during which time the hepatic concentration of triglyceride was declining, fatty acid was being oxidized, and triglyceride was not being released at normal rates. 4. 4. These observations were discussed in an attempt to evaluate the mechanisms by which the fatty liver develops in the intact alloxan-diabetic animal at a time when hepatic triglyceride catabolism appears to be increased.