Combined effects of chlorpromazine and high fat diet on lipid levels and enzyme activities in bile, liver and plasma of Wistar rats

The effects of high fat diet and injection of chlorpromazine on bile lipid secretion were studied in the rats fed a control diet (C), a saturated fat, high cholesterol diet (S) and a polyunsaturated fat, high cholesterol diet (PU). As compared to controls, injection of chlorpromazine in the S and PU diet groups caused no appreciable change in the level of bile salts and bile phospholipids. Chlorpromazine did however enhance bile cholesterol, especially in the PU group, and lower secretion of lysosomal enzyme (beta-glucuronidase) into bile. Impairment of lysosomal enzyme secretion but not of bile lipid secretion suggests that the lysosomal activity is not directly involved in the bile secretion mechanism. These data point up the risks of using chlorpromazine therapy in association with a diet high in fat and cholesterol.     

Phenotypic characterization of lith genes that determine susceptibility to cholesterol cholelithiasis in inbred mice. Pathophysiology Of biliary lipid secretion.

The inbred C57L strain but not the AKR strain of mice carry Lith genes that determine cholesterol gallstone susceptibility. When C57L mice are fed a lithogenic diet containing 15% fat, 1% cholesterol, and 0.5% cholic acid, gallbladder bile displays rapid cholesterol supersaturation, mucin gel accumulation, increases in hydrophobic bile salts, and rapid phase separation of solid and liquid crystals, all of which contribute to the high cholesterol gallstone prevalence rates (D. Q-H. Wang, B. Paigen, and M. C. Carey. J. Lipid Res. 1997. 38: 1395;-1411). We have now determined the hepatic secretion rates of biliary lipids in fasting male and female C57L and AKR mice and the intercross (C57L x AKR)F(1) before and at frequent intervals during feeding the lithogenic diet for 56 days. Bile flow and biliary lipid secretion rates were measured in the first hour of an acute bile fistula and circulating bile salt pool sizes were determined by the "washout" technique after cholecystectomy. Compared with AKR mice, we found that i) C57L and F(1) mice on chow displayed significantly higher secretion rates of all biliary lipids, and larger bile salt pool sizes, as well as higher bile salt-dependent and bile salt-independent flow rates; ii) the lithogenic diet further increased biliary cholesterol and lecithin outputs, but bile salt outputs remained constant. Biliary coupling of cholesterol to lecithin increased approximately 30%, setting the biophysical conditions necessary for cholesterol phase separation in the gallbladder; and iii) no gender differences in lipid secretion rates were noted but male mice exhibited significantly more hydrophobic bile salt pools than females.We conclude that in gallstone-susceptible mice, Lith genes determine increased outputs of all biliary lipids but promote cholesterol hypersecretion disproportionately to lecithin and bile salt outputs thereby inducing lithogenic bile formation.     

Effects of dietary soybean lecithin on plasma lipid transport and hepatic cholesterol metabolism in rats

Dietary lecithin can stimulate bile formation and biliary lipid secretion, particularly cholesterol output in bile. Studies also suggested that the lecithin-rich diet might modify hepatic cholesterol homeostasis and lipoprotein metabolism. Therefore, we examined hepatic activities of 3-hydroxy-3 methylglutaryl coenzyme A reductase "HMG -CoA reductase", cholesterol 7 alpha-hydroxylase and acyl-CoA: cholesterol acyltransferase "ACAT" as well as plasma lipids and lipoprotein composition in rats fed diets enriched with 20% of soybean lecithin during 14 days. We also evaluated the content of hepatic canalicular membrane proteins involved in lipid transport to the bile (all P-glycoproteins as detected by the C 219 antibody and the sister of P-glycoprotein "spgp" or bile acid export pump) by Western blotting. As predicted, lecithin diet modified hepatic cholesterol homeostasis. The activity of hepatic HMG-CoA reductase and cholesterol 7 alpha-hydroxylase was enhanced by 30 and 12% respectively, while microsomal ACAT activity showed a dramatic decrease of 75%. As previously reported from ACAT inhibition, the plasma level and size of very low-density lipoprotein (VLDL) were significantly decreased and bile acid pool size and biliary lipid output were significantly increased. The canalicular membrane content of lipid transporters was not significantly affected by dietary lecithin. The current data on inhibition of ACAT activity and related metabolic effects by lecithin mimic the previously reported effects following drug-induced inhibition of ACAT activity, suggesting potential beneficial effects of dietary lecithin supplementation in vascular disease.     

Dietary soybean phosphatidylcholines lower lipidemia: mechanisms at the levels of intestine, endothelial cell, and hepato-biliary axis

The beneficial metabolic effects of dietary soybean lecithin on lipid metabolism are now more clearly established. The intestinal absorption of cholesterol is decreased by soybean phosphatidylcholine-enriched diet and results in a cholesterol-lowering effect. There is an enhancement of the cholesterol efflux by endothelial cells incubated with soybean phosphatidylcholines, and a stimulation of the reverse cholesterol transport by high density lipoprotein-phosphatidylcholines. As a result of all these processes, phosphatidylcholines provided by the soybean lecithin metabolism appear to be key molecules controlling the biodynamic exchanges of lipids. They regulate homeostasis of cholesterol and fatty acids by decreasing their synthesis and promoting cholesterol oxidation into bile salts. Finally, the outcome is the increase in bile secretion of these lipids and/or their metabolite forms. Such findings constitute promising goals in the field of nutritional effects of soybean lecithin in the treatment or prevention of hyperlipidemia and related atherosclerosis.     

Effect of fat pre-feeding on bile flow and composition in the rat

Studies were conducted in rats to determine if the increase in lymph triacylglycerol output on pre-feeding a 20% glyceryltrioleate diet (Mansbach, C.M., II and Arnold, A. (1986) Am. J. Physiol. 251, G263-269) was due to an increase in phosphatidylcholine output into bile. Rats who were fed chow or pre-fed the 20% fat diet were equipped with biliary and duodenal cannulas and infused with glucose-saline while bile was collected hourly. The next day a taurocholate-glyceryltrioleate infusion was given and bile collected for 5 h. Bile flow, bile acid, phosphatidylcholine and cholesterol output were greater in the chow fed group than controls during the 6 h of the glucose saline period. Outputs were low overnight. During the taurocholate-glyceryltrioleate infusion, bile flow, bile acid, phosphatidylcholine and cholesterol output were all greater in the fat pre-fed group than the chow fed controls. We conclude that fat pre-feeding profoundly influences biliary composition and flow. The 2-fold increase in biliary phosphatidylcholine output during duodenal lipid infusion offers a potential explanation for the increased delivery of triacylglycerol into the lymph in rats on a similar fat pre-feeding program.     

Mathematical model of biliary lipid secretion: a quantitative analysis of physiological and biochemical data from man and other species

We propose a simple mathematical model to account for the coupling of secretion rates of bile salts, lecithin, and cholesterol into bile. The model assumes that: 1) molecules of "biliary" lecithin and cholesterol enter a functional compartment located in the endoplasmic reticulum of the hepatocyte from which they are secreted into bile, and in the case of cholesterol, also catabolized to bile salts; 2) the rates at which lecithin and cholesterol enter the "secretory" compartment are regulated independently by feedback loops that control their synthesis and/or uptake; 3) lecithin secretion is coupled by an unknown transport mechanism, possibly micellar or vesicular, to the flux of bile salts passing through the compartment; 4) cholesterol secretion is coupled by a similar mechanism to lecithin secretion and not to bile salt secretion directly; and 5) bile salt synthesis is proportional to the cholesterol content of the compartment. The model predicts that in the steady state the dependences, lecithin secretion vs bile salt secretion; cholesterol secretion vs lecithin secretion; and cholesterol secretion vs bile salt secretion, will all have the form of rectangular hyperbolae. Four independent parameters related to the postulated mechanisms of biliary lipid synthesis, uptake, and transport determine the quantitative features of these hyperbolae. These four "secretion parameters" also determine how the biliary lipid composition of hepatic and "fasting" gallbladder bile varies with bile salt secretion rate. A quantitative analysis of biochemical and physiological data on biliary lipid secretion in rat, dog, and man confirms the general predictions of the model. Deductions of the secretion parameters are made for each species and are compared with other relevant data on biliary lipid metabolism. From this analysis, we offer new insights into: i) the species differences in biliary lipid secretion and bile composition; ii) the influence of obesity on biliary lipid secretion in man; and iii) the causes of cholesterol super-saturation in fasting gallbladder bile.     

A histochemical study about changes in rat liver plasma membrane enzyme activities after galactosamine administration.

In rats changes in plasma membrane enzyme activities due to Gal-N intoxication were studied by enzymehistochemical methods. The bile canalicular 5'-nucleotidase and nucleoside polyphosphatase activities decreased; the sinusoidal 5'-nucleotidase remained unchanged. The bile canalicular leucyl-beta-naphthyl-amidase showed an increase in activity; the alkaline phosphatase activity remained unchanged. In contrast to the spotty necrosis, changes in plasma membrane enzyme activities were seen in all liver cells, suggesting that changes of these activities, occurring after Gal-N treatment, do not correlate with cell death. The conclusion was drawn that the deviations of the enzyme activities might be due to changes in the lipid environment of the enzyme proteins in the membrane. With the exception of alkaline phosphatase, partial hepatectomy caused the same changes in enzyme activities as did Gal-N intoxication. Nevertheless Gal-N administration to partial hepatectomized rats did not lead to hepatic necrosis. Galactose given simultaneously or within two hours after Gal-N prevented both changes in plasma membrane enzyme activities and hepatocellular damage. This suggests an important role of galactolipids and galactoproteins in the plasma membrane alterations.     

Solubilization of multilamellar liposomes of egg yolk lecithin by the bile salt sodiumtaurodeoxycholate and the effect of cholesterol--a rapid-ultrafiltration study

The solubilization of multilamellar egg yolk lecithin liposomes by sodiumtaurodeoxycholate in aqueous phase was studied by ultrafiltration as a function of time, bile salt and cholesterol concentration. The corresponding equilibrium states were analysed. Complete solubilization was achieved at total bile salt/lecithin molar mixing ratios of approximately 5. The minimum ratio to start solubilization was 0.1, corresponding to a free bile salt concentration of only 5% of the critical micelle concentration (CMC). Mean equilibrium constants for the partition of bile salts between non-filterable aggregates and filterable mixed micelles and also the free bile salt concentration were determined. Sodiumtaurodeoxycholate had a higher affinity for small mixed micelles than for lamellar mixed aggregates especially in the presence of cholesterol, which reduces the degree and rate of the solubilization process. A non-homogeneous distribution of bile salts in the lipid phase was detected at low bile salt concentrations.     

Dietary polyenylphosphatidylcholine decreases cholesterolemia in hypercholesterolemic rabbits: role of the hepato-biliary axis

The aim of this work was to study the cholesterol-lowering mechanisms induced by dietary soybean lecithin in hypercholesterolemic rabbits. Male New Zealand white rabbits (n = 6 in each group) were fed for 10 weeks either a low-fat control C diet, containing 27 g fat/kg, or high-fat diets enriched with 2 g cholesterol/kg and 77 g fat/kg. The high-fat diets contained 50 g lard (L), 50 g soybean triacylglycerol (SO), or 50 g pure soybean phosphatidylcholine (PLE). PLE diet decreased by 30% beta-VLDL-cholesterol, compared with SO diet. HDL2-, HDL3- and LDL-lipid contents were unchanged in the L, SO and PLE groups. In gallbladder bile, amounts of phospholipids, bile salts and cholesterol were significantly increased in PLE group by respectively 45%, 11% and 44%, in comparison with SO group. Intestinal and hepatic Hydroxy Methyl Glutaryl Coenzyme A reductase activities were not increased by PLE diet. Triacylglycerol hepatic content was lower in PLE group than in L or SO groups. Compared with triacylglycerol enriched diet, phosphatidylcholine enriched diet developed significant higher cholesterol- and triacylglycerol-lowering effects by a two-step mechanism: i) by reducing the beta-VLDLs, ii) by enhancing the secretion of bile cholesterol. Such results constitute promising effects of soybean phosphatidylcholine at the hepato-biliary level, in the treatment or prevention of hyperlipidemia and related atherosclerosis.     

Alterations in biliary lipids of mice during dehydrocholic acid feeding

Mice were fed a lithogenic diet consisting of Purina chow and 0.5% dehydrocholic acid (DHA group). Controls received Purina chow. Every 2 wk for 20 wk animals were killed, and biliary phospholipid, cholesterol, and bile salt concentrations were determined, as well as the extent of gallstone formation. With time there was a gradual, significant decline in the concentration and the relative composition of phospholipid in both groups compared with initial values. There was a significant increase in biliary cholesterol concentration and relative amount in the DHA group compared with the control. No significant differences were found in the relative amounts of bile salt or phospholipid between the two groups. Feeding DHA resulted in an increased concentration of bile salts and the sum of measured lipid compared with controls. After 8 wk, gallstones were found in approximately 60% of autopsied animals and correlated with increased cholesterol concentration. Our data support the hypothesis that there is a component of cholesterol secretion that may not be bile salt- or phospholipid-dependent. Our data also suggest that biliary phospholipid secretion decreases with age.     

Bile salts and calcium absorption

1. The study of the effect of bile salts on enhancing calcium absorption in the rachitic chick has been extended to bile salts not present in chick bile, e.g. glycine conjugates and bile alcohol sulphates. 2. Bile and bile salts cause an increase in calcium absorption from sparingly soluble calcium hydrogen phosphate when compared with a suspension of calcium hydrogen phosphate in saline. 3. If the bile ducts of normal rats are tied the absorption of calcium from calcium hydrogen phosphate decreases but can be restored by giving bile salts with the calcium salt. 4. Bile salts increase solubility in water of the sparingly soluble calcium salts, phytate and phosphate at pH values between 6 and 8. 5. Bile salts increase the solubility in lipid solvents of calcium in approximately the same proportion as they increase the absorption of calcium from the gut. 6. The physiological role of bile in calcium absorption and its mode of action are discussed.     

Influence of total lipid concentration, bile salt:lecithin ratio, and cholesterol content on inter-mixed micellar/vesicular (non-lecithin-associated) bile salt concentrations in model bile.

We modified classic equilibrium dialysis methodology to correct for dialysant dilution and Donnan effects, and have systematically studied how variations in total lipid concentration, bile salt (taurocholate):lecithin (egg yolk) ratio, and cholesterol content influence inter-mixed micellar/vesicular (non-lecithin-associated) concentrations (IMC) of bile salts (BS) in model bile. To simulate large volumes of dialysant, the total volume (1 ml) of model bile was exchanged nine times during dialysis. When equilibrium was reached, dialysate BS concentrations plateaued, and initial and final BS concentrations in the dialysant were identical. After corrections for Donnan effects, IMC values were appreciably lower than final dialysate BS concentrations. Quasielastic light scattering was used to validate these IMC values by demonstrating that lipid particle sizes and mean scattered light intensities did not vary when model biles were diluted with aqueous BS solutions of the appropriate IMC. Micelles and vesicles were separated from cholesterol-supersaturated model bile, utilizing high performance gel chromatography with an eluant containing the IMC. Upon rechromatography of micelles and vesicles using an identical IMC, there was no net transfer of lipid between micelles and vesicles. To simulate dilution during gel filtration, model biles were diluted with 10 mM Na cholate, the prevailing literature eluant, resulting in net transfer of lipid between micelles and vesicles, the direction of which depended upon total lipid concentration and BS/lecithin ratio. Using the present methodology, we demonstrated that inter-mixed micellar/vesicular concentrations (IMC) values increased strongly (5 to 40 mM) with increases in both bile salt (BS):lecithin ratio and total lipid concentration, whereas variations in cholesterol content had no appreciable effects. For model biles with typical physiological biliary lipid compositions, IMC values exceeded the critical micellar concentration of the pure BS, implying that in cholesterol-supersaturated biles, simple BS micelles coexist with mixed BS/lecithin/cholesterol micelles and cholesterol/lecithin vesicles. We believe that this methodology allows the systematic evaluation of IMC values, with the ultimate aim of accurately separating micellar, vesicular, and potential other cholesterol-carrying particles from native bile.     

Acute effects of filipin on the plasmic, hepatic, and biliary cholesterol of the rat

Twenty-one male Wistar rats, 13 weeks old, were fed ad libitum hyperlipidic diets (28% fats) loaded with cholesterol (1.2%) for 5 weeks. One group of 11 rats was fed saturated fats (diet group "S") and another group of 10 rats was fed polyunsaturated fats (diet group "PU"). On the day they were sacrificed 10 of the rats were injected intravenously with 1 mg of filipin. Contrary to the rats in diet group "PU," the rats in diet group "S" treated with filipin presented certain characteristics that were not found in the nontreated group: They provided evidence of biliary cholestasis accompanied by a decline in the level of secretion of bile salts and phospholipids into bile. The concentrations of both free and esterified cholesterol in plasma fell and the amount of (esterified) hepatic cholesterol rose, although there was no change due to the filipin in the amounts of hepatic phospholipids. Explanatory hypotheses for these phenomena were considered, first, at the site of plasma membranes where filipin binds selectively to the cholesterol in the membrane, causing a disruption which probably disturbs the absorbance of circulating lipoproteins, especially that of hepatocyte cells, particularly in diet group "PU." Second, the effects of filipin on subcellular membranes seem to disturb the secretion of lipids and lipoproteins into bile and plasma, especially in diet group "S." Last, at the intracellular level, filipin appears to have a blocking effect on the organelles involved in biliary lipid secretion. The activity of certain enzymes such as cholesterol esterase may also be blocked, particularly in diet group "S," which would explain the accumulation of esterified cholesterol in liver.     

Role of glutathione, lipid peroxidation and antioxidants on acute bile-duct obstruction in the rat

The aim of this work was to evaluate the role of lipid peroxidation and glutathione on liver damage induced by 7-day biliary obstruction in the rat. Male Wistar rats were bile-duct-ligated and divided in groups of 10 animals. Groups received vitamin E (400 IU/rat, p.o., daily) or trolox (50 mg/kg, p.o., daily) or both. Lipid peroxidation increased significantly in the livers of bile-duct-ligated rats. Vitamin E and trolox prevented lipid peroxidation. GSH was oxidized in the BDL group and the GSH/GSSG ratio decreased as a consequence. However, total glutathione content increased in liver and blood indicating a possible induction in de novo synthesis of GSH. Antioxidants preserved the normal GSH/GSSG ratio. Despite the observation that antioxidants verted lipid peroxidation and oxidation of GSH, liver injury (as assessed by serum enzyme activities, bilirubin concentration, liver glycogen content and histology) was not affected by the treatments. These results suggest that drugs that inhibit lipid peroxidation and oxidation of glutathione have no effect on conventional biochemical markers of liver injury and on liver histology of bile-duct-ligated rats for 7 days. It seems more likely that the detergent action of bile salts is responsible for solubilization of plasma membranes and cell death, which in turn may lead to oxidative stress, GSH oxidation and lipid peroxidation.     

Biochemical site of regulation of bile acid biosynthesis in the rat

The production of bile salts by rat liver is regulated by a feedback mechanism, but it is not known which enzyme controls endogenous bile acid synthesis. In order to demonstrate the biochemical site of this control mechanism, bile fistula rats were infused intravenously with (14)C-labeled bile acid precursors, and bile acid biosynthesis was inhibited as required by intraduodenal infusion of sodium taurocholate. The infusion of taurocholate (11-14 mg/100 g of rat per hr) inhibited the incorporation of acetate-1-(14)C, mevalonolactone-2-(14)C, and cholesterol-4-(14)C into bile acids by approximately 90%. In contrast, the incorporation of 7alpha-hydroxycholesterol-4-(14)C into bile acids was reduced by less than 10% during taurocholate infusion. These results indicate that the regulation of bile acid biosynthesis is exerted via cholesterol 7alpha-hydroxylase provided that hepatic cholesterol synthesis is adequate.     

Hypolipidemic effect of diet supplementation with bacterial levan in cholesterol-fed rats

Levan polysaccharide, a type of fructan, has been shown to have industrial applications as a new industrial gum in the fields of cosmetics, foods like dietary fiber and pharmaceutical goods. The objective of this current study was to investigate the possible hypolipidemic and antioxidative effects of levan in rats fed with a high-cholesterol diet. Animals were allocated into four groups of six rats each: a normal diet group (Control), normal rats received levan (L), a high-cholesterol diet group (Chol) and a high-cholesterol diet with a daily dose of levan equivalent to 5%. Treated hypercholesterolemic rats were administrated with levan in drinking water through oral gavage for 60 days. After the treatment period, the plasma antioxidant enzymes and lipid profiles were determined. Our results show that treatment with levan polysaccharide positively changed plasma antioxidant enzyme activities and lipid profiles (total cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides) in cholesterol-rats, and thus may have potential hypolipidemic and antioxidant effects. Levan could protect against oxidative stress linked atherosclerosis and decrease the atherogenic index.     

Prevention by dietary (n-6) polyunsaturated phosphatidylcholines of intrahepatic cholestasis induced by cyclosporine A in animals

Previous findings showed that dietary (n-6) polyunsaturated phosphatidylcholines (vegetable lecithin) could efficiently prevent intrahepatic cholestasis induced by cyclosporine A in rats. Mechanistic studies showed that expressions in rat liver of Na(+), K(+)-ATPase, Ca(2+), Mg(2+)-ATPase and F-actin were both decreased by drug administration and both enhanced by (n-6) lecithin enriched diet. There is a possible direct effect of phosphatidylcholines, vectors of polyunsaturated fatty acids provided by the metabolism of the dietary lecithin, on the aforesaid hepatic parameters. Such modulations by drug and diet result in reversed modifications of membrane composition and fluidity. Final outcome is decreased and enhanced bile lipid secretion by cyclosporine and vegetable lecithin enriched diet respectively. Moreover, we advance the hypothesis of a bypass process including a separate and functional actin-independent way for the non micellar and phospholipid-dependent secretion of bile lipids. The relationships between the ATPases, the microfilament components such as F-actin and the different transporters still remain to be clarified. Furthermore, one can speculate on beneficial effects in humans of diets enriched in vegetable lecithins that might prevent cholestasis induced by cyclosporine A.     

Effect of dietary inclusion of Lactobacillus acidophilus ATCC 43121 on cholesterol metabolism in rats

This study examined the effects of Lactobacillus acidophilus ATCC 43121 (LAB) on cholesterol metabolism in hypercholesterolemia-induced rats. Four treatment groups of rats (n = 9) were fed experimental diets: normal diet, normal diet+LAB (2 x 10(6) CFU/day), hypercholesterol diet (0.5% cholesterol, w/w), and hypercholesterol diet + LAB. Body weight, feed intake, and feed efficiency did not differ among the four groups. Supplementation with LAB reduced total serum cholesterol (25%) and VLDL + IDL + LDL cholesterol (42%) in hypercholesterol diet groups, although hepatic tissue cholesterol and lipid contents were not changed. In the normal diet group, cholesterol synthesis (HMG-CoA reductase expression), absorption (LDL receptor expression), and excretion via bile acids (cholesterol 7 alpha-hydroxylase expression) were increased by supplementation with LAB, and increased cholesterol absorption and decreased excretion were found in the hypercholesterol diet group. Total fecal acid sterols excretion was increased by supplementation with LAB. With proportional changes in both normal and hypercholesterol diet groups, primary bile acids (cholic and chenodeoxycholic acids) were reduced, and secondary bile acids (deoxycholic and lithocholic acids) were increased. Fecal neutral sterol excretion was not changed by LAB. In this experiment, the increase in insoluble bile acid (lithocholic acid) reduced blood cholesterol level in rats fed hypercholesterol diets supplemented with LAB. Thus, in the rat, L. acidophilus ATCC 43121 is more likely to affect deconjugation and dehydroxylation during cholesterol metabolism than the assimilation of cholesterol into cell membranes.     

Thyroid hormone differentially augments biliary sterol secretion in the rat. II. The chronic bile fistula model.

To further define thyroid hormone effects on bile acid synthesis and biliary lipid secretion, studies were done in chronic bile fistula rats. Euthyroid and methimazole-hypothyroid rats, with and without triiodothyronine (T3) injection, had total bile diversion for timed bile collections. With interrupted enterohepatic circulation, cholesterol absorption is negligible and bile acid secretion equals bile acid synthesis rate. Hypothyroid rats had diminished levels of bile acid synthesis and biliary secretion of cholesterol and phospholipid. Single dose T3 injection produced a 13-fold increase in bile cholesterol secretion and a 3-fold increase in phospholipid secretion, both initiated 12 h after T3. Bile acid synthesis increased by 50%, but the increase did not begin until 24 h after T3. Neither hypothyroidism nor T3 treatment abolished diurnal rhythms of bile acid synthesis and biliary lipid secretion. Inhibition of cholesterol synthesis with lovastatin resulted in a persistent 33% decrease in bile acid synthesis in euthyroid and hypothyroid rats, while bile cholesterol secretion only transiently decreased. Inhibition of cholesterol synthesis did not alter T3-induced bile cholesterol secretion, with a 10-fold increase seen. However, bile acid synthesis was not stimulated by T3 in the presence of lovastatin. We conclude that facilitated bile acid synthesis and biliary cholesterol secretion are early effects of T3 and may account for the hypocholesterolemia of T3. Cholesterol synthesis does not appear to be required for the T3-induced bile cholesterol secretion.     

A possible correlation between lipid hydration and lipid activation of the C55-isoprenoid alcohol phosphokinase apoprotein.

1. A direct method for determining the binding of triated water to lipids is described. The experimental conditions were practically identical to those previously employed (1974) in the determination of the cofactor activities of a series of oleyl-lipids in reactivation of the C55-isoprenoid alcohol phosphokinase apoprotein. 2. Active cofactor lipids (dioleyl lecithin, sodium oleate, 1-monoolein, 1-monomyristin)bound between 2.3 and 5.3 nmol 3H2O per nmol lipid, whereas less than 0.14 nmol 3H2O were bound per nmol of the inactive lipids (1,2- and 1,3-diolein, triolein, oleyl alcohol, methyl oleate, cholesteryl oleate). 3. When exposed to 3H2O vapour, the active lipids adsorbed between 1 and 2 nmol 3H2O per nmol lipid, whereas the inactive lipids adsorbed less than 0.1 nmol 3H2O per nmol lipid. 4. The active lipid cofactor, egg lecithin, bound more than twice as much 3H2O as egg phosphatidylethanolamine which was devoid of cofactor activity in the absence of detergent. 5. Appropriately hydrated lipid polar groups are concluded to be required for an alignment with polar amino acid side chains of the enzyme apoprotein in the formation of a mixed micellar lipoprotein complex. The enzyme reaction might occur at the resulting lipoprotein/water interface.