Uptake and metabolism of high-density lipoproteins by cultured rabbit hepatocytes.

The selective uptake and internalization of core components of high-density lipoproteins (HDL) were examined in primary monolayer cultures of rabbit hepatocytes. Using [14C]sucrose as a surface marker covalently attached to apolipoprotein and [3H]cholesteryl linoleyl ether as a core marker, there was a 5-6-fold greater internalization of cholesteryl ether than sucrose-labeled apolipoprotein during 48 h of culture. The rate of uptake of [3H]cholesteryl linoleyl ether was 263 +/- 29 ng apo HDL/mg cell protein per h during the initial 8 h of culture, but averaged 101 +/- 32 ng apo HDL/mg cell protein per h over the 48 h culture period. Concomitant with this apparent selective uptake of cholesteryl ester core, there was a change in the HDL size distribution, with the appearance of a distinct population of smaller 4.3 nm radius particles in addition to the originally predominant particles of 4.9 nm radius. This was associated with a significant reduction of cholesteryl ester as a percentage of lipoprotein mass from 15.5 +/- 1.2 to 11.0 +/- 1.2 (P less than 0.001) and a reduction in cholesteryl ester:protein mass ratio from 0.30 +/- 0.01 to 0.19 +/- 0.01 (P less than 0.001). There was no change in the mass ratio of HDL triacylglycerol to protein. Thus rabbit hepatocytes in culture exhibit the capacity to selectively extract cholesteryl ester from HDL and produce smaller HDL particles.

Increase in selective hepatic uptake of high-density lipoprotein cholesteryl esters in the fasted rabbit.

The selective hepatic uptake of high-density lipoprotein cholesteryl esters was determined in primary hepatocyte cultures of cells from normal, cholestyramine-fed and 48-h-fasted rabbits. The HDL was labeled in the apoprotein moiety with [14C]sucrose and in the core component with [3H]cholesteryl linoleyl ether. The uptake of the apoprotein label did not differ between groups (indicating no change in holoparticle HDL uptake), but in contrast, the uptake of the cholesteryl ether label was significantly increased in hepatocytes from cholestyramine-fed and fasted animals. After 40 h of culture, the ratio of 3H to 14C uptake was 4.96 in controls cells, 7.15 in cholestyramine-treated cells and 10.24 in fasted hepatocytes from short-term fasted animals. Thus short-term fasting was associated with a 2-fold increase in the selective hepatic uptake of HDL core components, indicating that selective hepatic uptake of HDL cholesteryl esters is a physiologically responsive process.

Bile acid synthesis by cultured rabbit hepatocytes: stimulation by three lipoprotein fractions.

Bile acid and cholesterol synthesis were measured in monolayer cultures of rabbit hepatocytes maintained in a defined culture medium. In the absence of lipoproteins, bile acid synthesis and secretion were correlated with cholesterol synthesis and were increased 245% by mevalonolactone (10 mM) and inhibited 45% by lovastatin (50 micrograms/ml) over 24 h. When included in the culture medium, normal rabbit plasma low-density and high-density lipoproteins increased bile acid synthesis and secretion by up to 140% of values obtained without lipoproteins in hepatocytes from normal or cholestyramine-fed rabbits. Three cholesterol-rich lipoprotein fractions (beta-very low density, low density and high density) also were isolated from rabbits fed 1% cholesterol for 14 days. When added to rabbit hepatocyte cultures, each fraction markedly increased hepatocellular cholesterol content, stimulated bile acid synthesis and secretion in a dose-dependent manner, and inhibited cholesterol synthesis from radioactive acetate. These data indicate that three different lipoprotein fractions can provide cholesterol for uptake and subsequent breakdown to bile acids by cultured rabbit hepatocytes.

Bile acid synthesis and secretion by rabbit hepatocytes in primary monolayer culture: comparison with rat hepatocytes.

Rabbit hepatocytes isolated after liver perfusion with collagenase were maintained in primary monolayer culture for periods up to 96 h. Bile acid synthesis and secretion was measured by capillary gas-liquid chromatography and by a rapid enzymatic-bioluminescence assay. As expected from the bile acid profile of rabbit gallbladder bile, cholic acid was the only bile acid synthesized in detectable amounts and was produced at a linear rate of 170 pmol/h per mg cell protein from 24 to 96 h in culture. Ketoconazole (20 microM) inhibited cholic acid synthesis and secretion by 78%, whereas the bile acids chenodeoxycholic acid (100 microM), deoxycholic acid (100 microM) or lithocholic acid (2 microM) had no effect. When rat hepatocytes were cultured under identical conditions, the rate of bile acid synthesis was found to be only 12 pmol/h per mg cell protein, a value in agreement with previous work. The large difference in rates of bile acid synthesis between rabbit and rat hepatocytes may be due to rapid loss of cytochrome P-450 from rat hepatocytes when placed in monolayer culture. Although reportedly active in cholesterol 7 alpha-hydroxylation, form 4 cytochrome P-450 levels in rabbit hepatocytes did not correlate with rates of bile acid synthesis.

Metabolism of high density lipoproteins by the perfused rabbit liver.

The role of the liver in the catabolism of high density lipoproteins (HDL) was examined in isolated perfused rabbit livers. Using 125I-labeled rabbit HDL the disappearance of labeled apolipoproteins from the perfusate was biphasic with 7% of the label removed after 20 min and a further 6% between 20 and 90 min. In contrast, with HDL labeled with [3H]cholesteryl esters 35% of label had been removed after 90 min. The effect of liver perfusion on HDL size and composition was further studied by recirculating rabbit HDL for 120 min. In control experiments HDL was incubated at 37 degrees C for 120 min with nonperfused media and with media that had been liver perfused. The added HDL was predominantly particles of 4.8-4.9-mm radius, and incubation with nonperfused and preperfused media produced no significant change in size. However, liver perfusion resulted in particles predominantly 4.2-4.3-mm radius. Hepatic perfusion also significantly reduced HDL cholesteryl ester composition as a percentage of lipoproteins mass from 13.3 +/- 2.2% in control incubations to 10.7 +/- 3.1% (p less than 0.001), and cholesteryl ester:protein mass ratio was reduced from 0.31 +/- 0.06 in control to 0.24 +/- 0.10 (p less than 0.001) after 120 min of liver perfusion. Thus interaction of rabbit HDL with rabbit liver results in smaller HDL particles significantly depleted of core cholesteryl esters.

Oesophageal stricture due to reflux oesophagitis in pregnancy. Case report.

A patient with persistent vomiting in pregnancy due to oesophageal stricture secondary to reflux oesophagitis is reported. Reflux oesophagitis is common during pregnancy but usually responds to small frequent meals, the avoidance of certain positions and simple antacid therapy. Where symptoms are persistent and become worse in late pregnancy we suggest that more energetic therapy in the form of cimetidine or alginate antacid mixture (Gaviscon) should be considered to prevent oesophageal stricture formation.

Industrial energy in transition: a petrochemical perspective.

The future growth of the petrochemical industry depends in part on the industry's ability to improve efficiency in the use of oil and gas feedstocks and to develop promising alternatives. Technological innovation is proving to be the key to the long-term viability of the industry. The next 6 to 7 years will be characterized by the commercialization of new technologies designed to improve the efficiency of petroleum as a feedstock. Union Carbide's advanced cracking reactor, now nearing the demonstration stage, exemplifies this type of effort. The increasing price of oil and gas will make coal-based synthesis gas more attractive as a feedstock, particularly for oxygenated petrochemical products. A further development involves the conversion of biomass, through fermentation, to useful chemical products and the gasification of municipal wastes to raise steam for electricity generation and as a possible, supplemental feedstock. By the year 2000, it is predicted that feedstocks from all sources other than oil and gas may constitute 10 to 14 percent of the total new material requirement for the petrochemical industry.