Role of endogenous and exogenous cholesterol in liver as the precursor for bile acids in rats

There is considerable evidence suggesting that compartmentalized functional pools of cholesterol in the liver contribute differently to the formation of bile acids as the precursor. The present paper deals with the incorporation of [1-¹⁴C]acetate and of [1,2-³H]cholesterol carried on lipoproteins (LDL and HDL) into biliary bile acids in perfused rat livers and bile-fistula rats. The results showed that endogenous cholesterol synthesized newly from [1-¹⁴C]acetate in the liver was incorporated into both cholic acid and chenodeoxycholic acid in a similar way, while exogenous lipoprotein-[1,2-³H]cholesterol delivered to hepatocytes from hepatic circulation was incorporated into chenodeoxycholic acid at a higher rate.     

Biosynthesis of fatty acids and sterols in relation to the antibiotic formation inOudemansiella mucida

The production of mucidin by the basidiomyceteOudemansiella mucida was negatively influenced by the application of D-glucitol as the main carbon source, the effect being independent of the growth rate of the mycelium. The rate of fatty acid synthesis was measured by incorporation of 1-¹⁴C-acetate. After 8 days of cultivation, the amount of fatty acids was approximately half that synthetized during cultivation on glucose. The specific rate of incorporation reached its maximum after seven days of cultivation. Incorporation of 2-¹⁴C-mevalonate into sterols was the same under the two sets of cultivation conditions. Acetate units from the degraded fatty acids are probably also utilized for antibiotic synthesis.     

BIOCHEMTCAL CHANGES IN THE BRAIN OF EXPERIMENTAL ANIMALS IN RESPONSE TO ELEVATED PLASMA HOMOCYSTINE AND METHIONINE

The effects of high plasma concentrations of homocystine and methionine on the free amino acids of brain have been examined. Incorporation of the label from [³⁵S]methionine into the free amino acid pools of rabbit brain was enhanced in response to high plasma homocystine or high plasma homocystine and mcthionine. Under comparable conditions a marked decrease in the incorporation of the label from [¹⁴C]glycine into the free pool was observed. The corresponding incorporation of ³⁵S and ¹⁴C into brain proteins parallelled the results obtained with incorporation into the free pools of amino acids. Amino acid analyses of the free amino acid pools of rabbit brain revealed a general decrease in the concentration of amino acids in response to high plasma homocystine or high plasma homocystine and methionine. Inhibition of protein synthesis which occurs under the above experimental conditions is a general phenomenon. myelin and other brain fractions being equally affected. The decrease in concentration of brain amino acids also results in a diminution in concentration of the neurotransmitters GABA, dopamine and noradrenaline. The possible relationship of the observed changes to homocystinuria is discussed.     

Similar effects ofβ-alanine and taurine in cholesterol metabolism

β-Alanine, though producing a deficiency of taurine in the tissues, had a similar effect on cholesterol metabolism as taurine. Both caused increased activity of hepatic hydroxymethylglutaryl coenzyme A reductase and increased incorporation of 1, 2 of [¹⁴C]-acetate into liver cholesterol. Both caused increased concentration of biliary cholesterol and bile acids. There was increased activity of lipoprotein lipase in heart, but decreased activity in the adipose tissue in both cases. Release of lipoproteins into circulation was decreased in both cases.     

Incorporation of carbon from glucose into cerebral amino acids, proteins and lipids, and alterations during recovery from hypoglycaemia

Abstract— [U-¹⁴C]Glucose was given to dogs by intravenous infusion to maintain a fixed level of specific radioactivity of the plasma glucose. The time course of incorporation of ¹⁴C into free amino acids, proteins and lipids of the cerebrum was observed for periods up to 2 h. Labelling of amino acids closely related to the tricarboxylic acid cycle increased progressively throughout the infusion, approaching specific radioactivities per μg-atom of carbon equal to that of the plasma glucose. No significant dilution by unlabelled carbon entering the metabolic pathways was apparent. In dogs subjected to profound insulin hypoglycaemia, [U-¹⁴C]glucose mixed with unlabelled glucose was given to bring about recovery. The incorporation of ¹⁴C into glutamate, glutamine and aspartate during a 40-min period was greater than during a comparable period in control animals, whereas the incorporation into serine was reduced. When considered in relation to alterations in amino acid levels, the data suggest that during recovery from hypoglycaemia the rates of synthesis of amino acids related to the tricarboxylic acid cycle are increased. During the period of recovery the rates of incorporation of ¹⁴C from glucose into proteins exceeded the pre-insulin rates to a degree surpassing the increased incorporation into free amino acids. The labelling of the ganglioside, cerebroside-sulphatide and cephalin fractions was also increased, The rates of incorporation into the lecithin-sphin-gomyelin and cholesterol fractions during recovery were the same as in the pre-insulin period. Hypoglycaemia decreased the cerebral content of the phospholipid fractions; the lecithin-sphingomyelin fraction returned toward normal during recovery, whereas the cephalins did not increase significantly. The electrographic patterns and the occurrence of convulsive activity are discussed, both in insulin hypoglycaemia and during recovery.     

The effects of electrical stimulation and ionic alterations on the metabolism of amino acids and proteins in excised superior cervical ganglia of the rat

Abstract— The effects of supramaximal electrical stimulation on the metabolism of amino acids and proteins in incubated superior cervical ganglia of the rat were studied by the use of a gas-liquid chromatographic (GLC) assay procedure. Stimulation at 5 Hz for 2 h caused an apparent increase in tissue levels of free amino acids, with alanine, serine, glycine, valine, threonine, isoleucine and aspartate (+ asparagine) most noticeably affected. The amino acid composition (partial) of the TCA-insoluble proteins of resting and stimulated ganglia was approximately the same after 60 min of incubation, but there was less TCA-insoluble protein in the stimulated ganglia. The addition of amino acids (at plasma concentrations) to the standard media had no apparent affect on the amino acid composition of this protein fraction. Stimulation for 0 , 5 h initially increased the efflux of alanine, valine, proline and ornithine into the incubation media but prolonged stimulation (for 4–0 h) decreased the efflux of alanine, serine, glycine and isoleucine and increased the efflux of lysine into the incubation media. The leakage of amino acids from the ganglia appeared to be a sodium-dependent process. The incorporation of ¹⁴C from [U-¹⁴C]glucose into glutamate (+ glutamine) and aspartate (+ asparagine) was greater in stimulated than in resting ganglia. However, the conversion of glutamate carbons from [U-¹⁴C]l -glutamate into aspartate was not affected by stimulation. Incorporation of ¹⁴C from [U-¹⁴C]glucose into glycine and serine was apparently not affected by stimulation during the 60 min of incubation. However, serine was the only amino acid which exhibited a higher specific radioactivity in stimulated ganglia than in resting ganglia incubated for 4 h in standard media. Lithium ions had the apparent specific effect of increasing the labelling with ¹⁴C from [U-¹⁴C]glucose into ornithine, and increasing the efflux and overall metabolism of serine in the ganglia. Incorporation of ¹⁴C from [U-¹⁴C]glucose into proteins was lower in the stimulated than in the resting ganglia if compensation was made for the higher radioactivity available in the total free amino acid pool of the stimulated ganglia. The rate of ¹⁴C incorporation from [U-¹⁴C]glutamate into the TCA-insoluble proteins of resting ganglia was greater when no other amino acids at concentrations approximating plasma levels were added to the bathing media; this rate was lower in stimulated than in resting ganglia.     

The synthesis of bile acids in perfused rat liver subjected to chronic biliary drainage

1. Isolated rat liver was perfused with heparinized whole blood under physiological pressure resulting in the secretion of bile at about the rate observed in vivo. 2. The preparation remained metabolically active for 4h and was apparently normal in function and microscopic appearance. 3. When the perfusate plasma and liver cholesterol pool was labelled by the introduction of [2-(14)C]mevalonic acid the specific radioactivity of the perfusate cholesterol increased. The biliary acids (cholic acid and chenodeoxycholic acid) were labelled and had the same specific radioactivity. 4. Livers removed from rats immediately after, and 40h after, the start of total biliary drainage, were perfused; increased excretion rates of both cholic acid and chenodeoxycholic acid were found when the liver donors had been subjected to biliary drainage. 5. The incorporation of [2-(14)C]mevalonic acid or rat lipoprotein labelled with [(14)C]cholesterol into bile acids was studied. 6. A dissociation between the mass of bile acid excreted and the rate of incorporation of (14)C was found. This was attributed to the changing specific radioactivity of the cholesterol pool acting as the immediate bile acid precursor.     

Cholesterol gallstones in alloxan-diabetic mice

Normal and alloxan-diabetic male mice (Crj-ICR) were fed a diet containing 0.5% cholesterol for 5 and 10 weeks, and gallbladder bile was analyzed for cholesterol, phospholipids and bile acids, feces for sterols and bile acids, and plasma and liver for cholesterol, phospholipids, and triglycerides. Normal mice developed no gallstones but the diabetic mice developed cholesterol gallstones with an incidence of 70% by 5 weeks and 80% by 10 weeks after feeding of the cholesterol diet. Diabetic mice fed the ordinary diet also developed stones (23%) by 10 weeks. In the diabetic mice, the gallbladder was enlarged about threefold, and biliary lipid concentration, diet intake, and fecal excretion of sterols and bile acids increased but body weight decreased. Cholic acid and beta-muricholic acid comprised over 40% each of the total biliary bile acids in normal mice, but cholic acid increased to about 80% and beta-muricholic acid decreased to a few percent in the diabetic mice. Fecal excretion of bile acids increased after cholesterol feeding in both normal and diabetic mice, but the increased bile acid in the normal animals was beta-muricholic acid and that in the diabetic mice was deoxycholic acid. The mice that developed gallstones showed a marked increase in biliary cholesterol value and decreases in gallbladder bile and bile acid concentration, but no difference in biliary and fecal bile acid composition, bile acid synthesis, fecal sterols, or plasma and liver lipid levels. Cholesterol absorption was increased in the diabetic mice when examined by plasma 14C/3H ratio and fecal 14C-labeled sterol excretion after a single oral administration of [14C]cholesterol and a simultaneous intravenous injection of [3H]cholesterol. These data led to the conclusion that cholesterol gallstones developed in alloxan-diabetic mice fed excess cholesterol, due to the hyperphagia and the enhancement of cholesterol absorption caused by increases in the synthesis and secretion of cholic acid.     

Hepatic SR-BI, not endothelial lipase, expression determines biliary cholesterol secretion in mice

High density lipoprotein cholesterol is thought to represent a preferred source of sterols secreted into bile following hepatic uptake by scavenger receptor class B type I (SR-BI). The present study aimed to determine the metabolic effects of an endothelial lipase (EL)–mediated stimulation of HDL cholesterol uptake on liver lipid metabolism and biliary cholesterol secretion in wild-type, SR-BI knockout, and SR-BI overexpressing mice. In each model, injection of an EL expressing adenovirus decreased plasma HDL cholesterol (P < 0.001) whereas hepatic cholesterol content increased (P < 0.05), translating into decreased expression of sterol-regulatory element binding protein 2 (SREBP2) and its target genes HMG-CoA reductase and LDL receptor (each P < 0.01). Biliary cholesterol secretion was dependent on hepatic SR-BI expression, being decreased in SR-BI knockouts (P < 0.001) and increased following hepatic SR-BI overexpression (P < 0.001). However, in each model, biliary secretion of cholesterol, bile acids, and phospholipids as well as fecal bile acid and neutral sterol content, remained unchanged in response to EL overexpression. Importantly, hepatic ABCG5/G8 expression did not correlate with biliary cholesterol secretion rates under these conditions. These results demonstrate that an acute decrease of plasma HDL cholesterol levels by overexpressing EL increases hepatic cholesterol content but leaves biliary sterol secretion unaltered. Instead, biliary cholesterol secretion rates are related to the hepatic expression level of SR-BI. These data stress the importance of SR-BI for biliary cholesterol secretion and might have relevance for concepts of reverse cholesterol transport.     

Liver-specific transgenic expression of cholesteryl ester hydrolase reduces atherosclerosis in Ldlr−/− mice

The liver plays a central role in the final elimination of cholesterol from the body either as bile acids or as free cholesterol (FC), and lipoprotein-derived cholesterol is the major source of total biliary cholesterol. HDL is the major lipoprotein responsible for removal and transport of cholesterol, mainly as cholesteryl esters (CEs), from the peripheral tissues to the liver. While HDL-FC is rapidly secreted into bile, the fate of HDL-CE remains unclear. We have earlier demonstrated the role of human CE hydrolase (CEH, CES1) in hepatic hydrolysis of HDL-CE and increasing bile acid synthesis, a process dependent on scavenger receptor BI expression. In the present study, we examined the hypothesis that by enhancing the elimination of HDL-CE into bile/feces, liver-specific transgenic expression of CEH will be anti-atherogenic. Increased CEH expression in the liver significantly increased the flux of HDL-CE to bile acids. In the LDLR^−/− background, this enhanced elimination of cholesterol led to attenuation of diet-induced atherosclerosis with a consistent increase in fecal sterol secretion primarily as bile acids. Taken together with the observed reduction in atherosclerosis by increasing macrophage CEH-mediated cholesterol efflux, these studies establish CEH as an important regulator in enhancing cholesterol elimination and also as an anti-atherogenic target.     

Control of fatty acid incorporation in membrane phospholipids. X-ray-induced changes in fatty acid uptake by tumor cells

Lymphosarcoma cells isolated from the spleens of tumor-bearing mice were used to study the effect of a low dose of X-rays (5 Gy) on the incorporation of [³H]palmitate and [¹⁴C]arachidonate into the lipids of the tumor cells. Palmitate and arachidonate were rapidly incorporated especially into the phospholipids of the cells. Between one and three hours after the start of the incubation with radiactive palmitate 80–90% of the label of the total lipids was found in the phospholipid fraction. Already after a few minutes of incubation with radioactive arachidonate, about 95% of the label was incorporated in the phospholipids. Irradiation caused a small but significant increase in the rate of fatty acid incorporation for both fatty acids. Concomitantly, a significantly increased amount of fatty acid was removed from the medium by the cells as a result of the irradiation, and the specific radioactivity of the free fatty acids in the cells was found to be enhanced. The radiation effect on the tumor cells could be mimicked by a hypotonic treatment. The magnitude of the radiation-induced stimulation of the fatty acid incorporation was similar to that of the hypotonically induced effect. Cells which had received a hypotonic treatment before the irradiation, did not show an additional radiation-induced enhancement of fatty acid incorporation into the cellular lipids. When the cells were incubated with serum albumin loaded with a relatively large (non-physiological) amount of complexed fatty acids (fatty acid: albumin molar ratio, $\text{ν}\text{= 3.7}$), no radiation effect on the fatty acid incorporation could be detected. It is concluded that hypotonic treatment, irradiation, and increased supply of exogenous fatty acids all lead to an enhanced flux of fatty acids into the cells. These results confirm our previous suggestion that the uptake of fatty acids through the plasma membrane is the rate-limiting step in the fatty acid incorporation into the phospholipids and that ionizing radiation is one of the means to enhance fatty acid uptake through the plasma membrane leading to an increased incorporation into the phospholipids.     

Hypolipidemic principle of the inflorescence stalk of plantain (Musa sapientum)

A pectin present in the juice of the inflorescence stalk of plantain(Musa sapientum) has been isolated. The material contained 32.4% hexoses and 52.5% uronic acid. On administration to rats fed both cholesterol free and cholesterol diet, this material showed significant lowering of cholesterol and triglycerides in the serum, liver and aorta. There was decreased cholesterogenesis in the liver as was evident from decreased activity of hydroxymethylglutaryl coenzyme A reductase and decreased incorporation of labelled acetate into hepatic cholesterol. Hepatic bile acids showed significant increase and there was increased fecal excretion of neutral sterols and bile acids. Release of lipoproteins into the circulation was lower. The material also caused increase in the activity of lipoprotein lipase in the heart and adipose tissue and also of plasma lecithin: cholesterol acyl transferase     

Cholecystokinin Elevates Mouse Plasma Lipids

Cholecystokinin (CCK) is a peptide hormone that induces bile release into the intestinal lumen which in turn aids in fat digestion and absorption in the intestine. While excretion of bile acids and cholesterol into the feces eliminates cholesterol from the body, this report examined the effect of CCK on increasing plasma cholesterol and triglycerides in mice. Our data demonstrated that intravenous injection of [Thr28, Nle31]-CCK at a dose of 50 ng/kg significantly increased plasma triglyceride and cholesterol levels by 22 and 31%, respectively, in fasting low-density lipoprotein receptor knockout (LDLR^−/−) mice. The same dose of [Thr28, Nle31]-CCK induced 6 and 13% increases in plasma triglyceride and cholesterol, respectively, in wild-type mice. However, these particular before and after CCK treatment values did not achieve statistical significance. Oral feeding of olive oil further elevated plasma triglycerides, but did not alter plasma cholesterol levels in CCK-treated mice. The increased plasma cholesterol in CCK-treated mice was distributed in very-low, low and high density lipoproteins (VLDL, LDL and HDL) with less of an increase in HDL. Correspondingly, the plasma apolipoprotein (apo) B48, B100, apoE and apoAI levels were significantly higher in the CCK-treated mice than in untreated control mice. Ligation of the bile duct, blocking CCK receptors with proglumide or inhibition of Niemann-Pick C1 Like 1 transporter with ezetimibe reduced the hypercholesterolemic effect of [Thr28, Nle31]-CCK in LDLR^−/− mice. These findings suggest that CCK-increased plasma cholesterol and triglycerides as a result of the reabsorption of biliary lipids from the intestine.     

Dynamics of amino acids in pea stem sections during root formation and its inhibition by kinetin and ethionine

An investigation was conducted to study the interrelation of free amino acid metabolism and root formation in etiolated pea stem sections as dependent on time and on inhibition of root formation by kinetin and ethionine. The rise in the level of aspartic acid and increase in the rate of conversion of¹⁴C-labeled glucose to free amino acids were found to be characteristic features of the formation of foci of meristematic cells in pericyclo region. The formation of roots was reflected, in general, much more in the rate of conversion of labeled glucose to free amino acids than in the levels of corresponding amino acids. The total amount of free amino acids was not significantly changed during incubation of stem sections in a solution of kinetin (5×10^?5 m). A rapid fall in their level was recorded in the next 24 hours. The incorporation of¹⁴C from glucose into a precursor of lignin, phenylalanine, was completely inhibited by kinetin which stimulated simultanously the growth of adjacent buds. Stimulation of secondary xylem formation, which appeared later, was accompanied by the resumption of¹⁴C-incorporation into phenylalanine. Inhibition of root formation by ethionine resulted in the rapid fall of the level of most amino acids and in a significant decrease in the rate of incorporation of¹⁴C from glucose into amino acids. A decreasing level of ethionine in tissues during cultivation of ethionine-treated stem sections was accompanied by a gradual rise in the individual amino acids and in the rate of conversion of glucose into free amino acids.     

Acylation of lysine residues in human plasma high density lipoprotein increases stability and plasma clearance in vivo

Although human plasma high density lipoproteins (HDL) concentrations negatively correlate with atherosclerotic cardiovascular disease, underlying mechanisms are unknown. Thus, there is continued interest in HDL structure and functionality. Numerous plasma factors disrupt HDL structure while inducing the release of lipid free apolipoprotein (apo) AI. Given that HDL is an unstable particle residing in a kinetic trap, we tested whether HDL could be stabilized by acylation with acetyl and hexanoyl anhydrides, giving AcHDL and HexHDL respectively. Lysine analysis with fluorescamine showed that AcHDL and HexHDL respectively contained 11 acetyl and 19 hexanoyl groups. Tests with biological and physicochemical perturbants showed that HexHDL was more stable than HDL to perturbant-induced lipid free apo AI formation. Like the reaction of streptococcal serum opacity factor against HDL, the interaction of HDL with its receptor, scavenger receptor class B member 1 (SR-B1), removes CE from HDL. Thus, we tested and validated the hypothesis that selective uptake of HexHDL-[³H]CE by Chinese Hamster Ovary cells expressing SR-B1 is less than that of HDL-[³H]CE; thus, selective SR-B1 uptake of HDL-CE depends on HDL instability. However, in mice, plasma clearance, hepatic uptake and sterol secretion into bile were faster from HexHDL-[³H]CE than from HDL-[³H]CE. Collectively, our data show that acylation increases HDL stability and that the reaction of plasma factors with HDL and SR-B1-mediated uptake are reduced by increased HDL stability. In vivo data suggest that HexHDL promotes charge-dependent reverse cholesterol transport, by a mechanism that increases hepatic sterol uptake via non SR-B1 receptors, thereby increasing bile acid output.     

Biochemical and Molecular Responses to Loss of Renal Mass: Membranes and Protein Synthesis: Metabolic Response to Renal Compensatory Growth

Forty-eight hours after unilateral nephrectomy in young male Sprague-Dawley rats the concentrations of free methionine, alanine and tyrosine in renal cortical tissue were increased by 15-65 percent while the corresponding plasma concentrations decreased by 23-35 percent. The renal cortical concentrations of valine and leucine increased by 41 percent and 26 percent while plasma concentrations remained unchanged. The cortical concentrations of ornithine, serine and threonine remained unchanged while the plasma concentration decreased by approximately one-third. The total free amino acid contained in the cortex was not changed, while total free amino acids in plasma decreased by 7 percent. These data are thought to reflect an increased uptake of methionine and tyrosine into renal cells during compensatory hypertrophy, and an increased incorporation into renal protein of serine, threonine and ornithine. All these changes as well as all other biochemical changes accompanying compensatory hypertrophy with the exception of an increase of the RNA/DNA ratio were prevented by starvation for 48 hours after unilateral nephrectomy.In young male Sprague-Dawley rats and adult male Charles River mice, the incorporation of ¹⁴C-choline into acid-insoluble phospholipids (phosphatidylcholine, lysophosphatidylcholine and sphingomyelin) was already accelerated 5 minutes after contralateral nephrectomy and further rose to +68 ± 7 percent within 20 minutes to 3 hours. Incorporation of ¹⁴C-choline into phospholipids remained accelerated for two to three days and reflected increased rates of phospholipid synthesis rather than increased choline uptake. Three hours after unilateral nephrectomy in mice, incorporation of i.p. injected ¹⁴C-choline into phospholipids was accelerated 25 percent. The rate of turnover of free labelled renal phospholipids was not accelerated during compensatory renal growth. The very early increase of choline incorporation into phospholipids after contralateral nephrectomy, therefore, appears to reflect an increased rate of synthesis of membrane material.     

Uric acid in nucleic and amino acid synthesis in the boll weevil, Anthonomus grandis

When uric acid-2-¹⁴C was injected into the boll weevil, Anthonomus grandis, it was metabolized to RNA, DNA, amino acid, and ¹⁴CO₂ at the end of 2 hr. The free amino acids, lipoamino acids, and protein amino acids were all labelled with the free amino acids showing the highest specific activity. Incorporation in DNA was slight, but it was extensive in RNA; cytidylic acid showed the greatest amount of incorporation.     

Bile formation and hepatic plasma membrane composition in guinea-pigs and rats

We compared bile formation, and biliary and liver plasma membrane composition in guinea-pigs and rats in an attempt to explain the observation that the bile flow rate and the bile acid independent fraction of bile flow (BAIF) in guinea-pigs is about five to seven times higher than in rats. Analysis of electrolytes in bile showed that bicarbonate was significantly [acid] higher in guinea-pigs while Cl⁻, phosphate and Ca²⁺ were markedly lower than in rats. High bile independent secretion in guinea-pigs was associated with a significantly lower concentration of total bile acid, phospholipid and cholesterol than in rats. Bile acid distribution studies showed that glycine conjugated chenodeoxycholate and ketolithocholate were the main bile acids in guinea-pigs, while taurine conjugated cholate and muricholate were the predominant bile acids in rats. Total fatty acid analysis of bile indicated that in rats the major fatty acids were palmitic acid (C16:0) and linoleic acid (C18:2, n-6). In guinea-pigs, the contribution of these fatty acids was lower than in rats and compensated with a significantly higher percentage of oleic acid (C18:1, n-9). Concentrations of anionic polypeptide fraction (APF), an acidic calcium binding apoprotein closely associated with biliary phospholipid and cholesterol secretion was also significantly lower in guinea-pigs. Canalicular plasma membrane analysis showed that as compared with rats, specific activities of Na⁺,K⁺ ATPase, and cholesterol and phospholipid content were markedly lower in guinea-pigs. Total fatty acid analysis of the membrane revealed that palmitic acid (C16:0), stearic acid (C18:0) and linoleic acid (C18:2, n-6) were the predominant fatty acids in guinea-pigs, while palmitic acid (C16:0), stearic acid (C18:0) and arachidonic acid (C20:4, n-6) were the most important in rats. Thus, high bile flow rate and BAIF in the guinea-pig may be attributed to the low bile acid concentration (below the critical micellar concentration), secretion of hypercholeretic bile acids (e.g. ketolithocholate) and high bicarbonate output.     

Hepatic uptake and metabolism of free cholesterol from different lipoprotein classes. An in vivo study in the rat

Hepatic metabolism of [14C]cholesterol, vehiculated by LDL, HDL2 and HDL3 lipoprotein particles, has been studied in rats with a permanent biliary drainage. The lipoprotein fractions were infused individually by a jugular vein catheter and bile was collected for 180 min after the administration. At the end of this period, the animals were killed and the blood and livers were collected. The free cholesterol of the HDL2 fraction was secreted into bile, mainly as bile salt, preferentially to that associated with HDL3 and LDL fractions (11.7% vs. 2.3% and 0.3%, respectively). The free cholesterol of the HDL3 fraction, on the other hand, was taken up by liver more quickly and in a higher proportion than that associated with other lipoprotein fractions. The label incorporation in this lipoprotein fraction was secreted earlier and not transformed into bile. The contribution of LDL-vehiculated free cholesterol to bile secretion was small and the hepatic uptake amounted to no more than 12% of the injected label.     

The incorporation of glycerol and lysine into the lipid fraction of Staphylococcus aureus

1. Incubation of washed cells of Staphylococcus aureus with [1-¹⁴C]glycerol results in the incorporation of glycerol into the lipid fraction of the cells. The rate of incorporation is increased by the presence of glucose and amino acids. The presence of amino acids increases incorporation into the fraction containing O-amino acid esters of phosphatidylglycerol. 2. Glycerol, incorporated into washed cells by incubation with glycerol, glucose and amino acids, is rapidly released from the lipid fraction when cells are incubated at low suspension densities in buffer. 3. Of nine amino acids tested, only lysine is significantly incorporated into the lipid fraction. The incorporation is increased by the presence of glycerol, glucose and other amino acids, especially aspartate and glutamate. 4. The incorporation of lysine is increased by the addition of puromycin at concentrations that inhibit protein synthesis. Chloramphenicol does not increase the incorporation of lysine but abolishes the enhancing effect of puromycin. 5. The enhancing effect of puromycin is accompanied by a similar increase in the incorporation of lysine into the fraction soluble in hot trichloroacetic acid. 6. Lysine is incorporated into the lipid fraction that contains O-amino acid esters of phosphatidylglycerol and corresponds in properties to phosphatidylglyceryl-lysine. 7. Lysine is rapidly released from the lipid of cells incubated in buffer only at low suspension densities. 8. Incubation of cells with the phosphatidylglyceryl-lysine fraction does not lead to the appearance of free lysine or to incorporation into the fraction insoluble in hot trichloroacetic acid.