Search PubMed⌕ Search

Biomedical subjects

M J Whiting

Publications and source records attributed to M J Whiting.

At least 37 records · Page 2Linked to original sources
PubMed1985

Cholesterol gallstone pathogenesis: a study of potential nucleating agents for cholesterol crystal formation in bile.

Cholesterol monohydrate crystal formation was measured quantitatively in model bile solutions, which were supersaturated with cholesterol, by a radiochemical method and qualitatively in human gallbladder bile by polarizing microscopy. Various agents, which have been postulated to act as nucleating factors for cholesterol crystal and gallstone formation, were added to bile and their effect on the appearance of cholesterol crystals was determined. These agents included calcium salts found in gallstones (calcite, aragonite, apatite, bilirubinate), Escherichia coli bacteria, pigment residues from cholesterol gallstones, bilirubin and several mucin preparations. Human gallbladder bile, which was collected from patients with and without cholesterol gallstones, was also mixed with model bile to examine whether nucleating or anti-nucleating factors were present. None of the agents tested markedly and consistently promoted cholesterol monohydrate crystal formation in model or human bile, except seed crystals of cholesterol monohydrate which were used as a control. Human gallbladder bile from obese patients without gallstones delayed the appearance of cholesterol crystals in model bile solutions, whereas gallbladder bile from gallstone patients did not. These results do not provide experimental support for the hypothesis that calcium salts and pigment material found in gallstones, or gallbladder mucin at concentrations less than 10 mg/ml, act as nucleating agents for cholesterol crystal and stone formation. The difference between gallbladder biles from patients with and without gallstones in their propensity to form cholesterol crystals may be due to the presence of an anti-nucleating factor in normal bile.

Animals↗
PubMed1984

Comparison of a monitored dose with a standard dose of chenodeoxycholic acid for gallstone dissolution.

The ability of chenodeoxycholic acid to dissolve gallstones was compared using different dosage regimens in two groups of 21 patients. The groups were closely matched for patient factors and stone characteristics known to influence the outcome of dissolution treatment. The patients in one group received a standard dose of chenodeoxycholic acid (15 mg/kg/day) taken at mealtimes. The patients in the second group received a bedtime dose of chenodeoxycholic acid which was sufficient to result in a proportion of this bile acid of 70% in the bile acid pool. This dose was monitored using serum bile acid profiles and varied within this test group (range 5.1-13.9 mg/kg/day). The number of patients whose stones completely dissolved in 12 months was similar in the standard-dose (7 of 21) and monitored-dose (8 of 21) groups. These results suggest that a bedtime dose of chenodeoxycholic acid, which is monitored to produce a level of 70% chenodeoxycholic acid in the biliary bile acid pool, is lower than the standard dose taken after meals but is of comparable efficacy. Lower dosage has the advantage of reducing costs and side effects from the drug, although serum bile acid profiling increases the cost of treatment.

Adult↗
PubMed1984

The cholesterol saturation of bile and its reduction by chenodeoxycholic acid in massively obese patients.

Massively obese patients are at high risk for developing cholesterol gallstones. The objectives of this study were to determine the influence of massive obesity on the cholesterol saturation of bile, and to examine the effect of massive obesity on the ability of chenodeoxycholic acid to decrease biliary cholesterol saturation. Gallbladder bile collected at surgery from massively obese patients was significantly more saturated with cholesterol than bile from non-obese patients who were matched for age, sex and gallstone status (P less than 0.01). Median biliary cholesterol saturation index values for groups of subjects were: no gallstones-not obese (0.83); no gallstones-obese (1.14); gallstones-not obese (1.08); gallstones-obese (1.37). Furthermore, a 5-week course of chenodeoxycholic acid (6 mg/kg/day) was less effective in reducing biliary cholesterol saturation in massively obese patients. The bile of 4 of 10 obese patients remained supersaturated, compared to only one of 10 non-obese patients. These results indicate that biliary cholesterol saturation is raised in massive obesity and that in this condition, the biliary lipid response to chenodeoxycholic acid is diminished. This may explain why obese patients have a relatively poor response to gallstone dissolution therapy with this bile acid.

Adult↗
PubMed1984

Supersaturated bile from obese patients without gallstones supports cholesterol crystal growth but not nucleation.

Cholesterol crystal formation was studied in gallbladder bile samples collected from 18 patients with cholesterol gallstones, 6 patients with black pigment stones, and 14 obese patients without gallstones. In the absence of seed crystals, bile from patients with cholesterol stones showed a much greater tendency to form cholesterol crystals in vitro than bile of similar cholesterol saturation from patients without cholesterol stones. The ability to form crystals was not related to the biliary hexosamine concentration, an indicator of mucin content. When small seed crystals of cholesterol monohydrate were added to each bile, the seed crystals dissolved in all biles (n = 8) with a cholesterol saturation index less than 0.76. In contrast, 29 of 30 biles with a cholesterol saturation index greater than 0.76 supported crystal growth, even when collected from patients without gallstones. These results indicate that the difference between supersaturated biles in the ability to form cholesterol crystals resides at the nucleation, rather than the growth, stage of crystal formation.

Adult↗
PubMed1983

Chemical and physical properties of gall stones in South Australia: implications for dissolution treatment.

Of 406 consecutive patients with gall-bladder stones, 387 were treated by cholecystectomy and 19 were treated with chenodeoxycholic acid. The gall stones found in 356 of the 387 patients at operation were analysed chemically for cholesterol and calcium, physically for number, size, and mass, and radiologically before cholecystectomy for stone lucency. Gall stones rich in cholesterol (greater than 80% by weight) were present in 75% of patients, while pigment stones (less than 25% cholesterol) were found in 12% of patients. Out of the 406 gall-stone patients, 77 (19%) had functioning gall bladders which contained radiolucent stones 1.5 cm or less in diameter, thereby fulfilling the criteria which are used by most clinicians in selecting patients for dissolution therapy of cholesterol gall stones. The stones of 61 of these patients were available for chemical analysis and 52 (85%) were rich in cholesterol. Using the more stringent criterion for stone size of 1 cm or less in diameter, only 11% of patients had stones suitable for dissolution treatment. Taking into account other factors such as lack of compliance with treatment, obesity, and calcium salts in gall stones, it appears that no more than 10% of gall-stone patients presenting to a general hospital could be successfully treated with chenodeoxycholic acid.

Adult↗
PubMed1983

Effect of synthetic oestrogens and progestagens in oral contraceptives on bile lipid composition.

The prevalence of cholesterol gall stones in young women has increased since the introduction of oral contraceptives. The synthetic female sex hormones used in these preparations, increase the degree of cholesterol saturation in bile. To determine whether oestrogens, progestagens, or both, are responsible for the change in biliary cholesterol saturation index, a prospective randomised, controlled study was performed. A significant increase in the cholesterol saturation index of bile was observed when either 30 micrograms ethinyloestradiol plus 150 micrograms norgestrel (p = 0.01) or 50 micrograms ethinyloestradiol plus 250 micrograms norgestrel (p less than 0.01) were ingested daily for two months. No change in the cholesterol saturation index was observed when 30 micrograms ethinyloestradiol alone, or 30 micrograms ethinyloestradiol plus 2.5 mg norethisterone were used. The mechanism for the increase in cholesterol saturation index did not appear to involve bile acid metabolism. These results indicate that the progestagen, norgestrel, and not as previously thought the oestrogen, ethinyloestradiol, is responsible for the increase in cholesterol saturation of bile which accompanies the use of oral contraceptives.

Adult↗
PubMed1983

Chenodeoxycholic acid administration monitored by serum bile acid profiles: a dose-response study.

Serum bile acid analysis was used to monitor the bile acid composition of bile in 16 healthy male volunteers before and during the oral administration of different doses of the gallstone-dissolving bile acid, chenodeoxycholic acid. Daily chenodeoxycholic acid ingestion increased the percentage of this bile acid in bile to a new steady-state level after two to three weeks. Doses of 125, 250, 500, and 750 mg/day significantly increased the proportion of chenodeoxycholic acid in bile from 41% to 55, 61, 78, and 79%, respectively, during the fourth week of ingestion. The results indicate that useful information concerning chenodeoxycholic acid-induced changes in the bile acid composition of bile can be obtained solely by serum bile acid analysis, and bile collection by duodenal intubation can be avoided.

Adult↗
PubMed1983

Cholesterol crystal formation and growth in model bile solutions.

Cholesterol monohydrate crystal formation was studied in supersaturated model bile solutions, containing unlabeled cholesterol, sodium cholate and soybean phosphatidylcholine, and tracer amounts of [3H]cholesterol. Solutions were either seeded with cholesterol crystals to initiate growth, or not seeded to allow self-nucleation and subsequent crystal growth to occur. Crystal growth at 37 degrees C was measured by two methods. First, radioactive cholesterol crystals were isolated by filtration, and the mass of cholesterol that had precipitated was calculated. In unseeded solutions, there was a long lag period before crystal growth was detected. This lag time was decreased by increases in the cholesterol concentration, temperature, and lipid concentration. In seeded solutions, crystal growth also was dependent on the cholesterol concentration, temperature, and lipid concentration. The second method used to measure crystal growth involved the Coulter Counter. At 37 degrees C, reproducible results were not obtained using unseeded solutions due to blocking of the counter aperture with large crystals. In seeded solutions, crystal growth could be measured as an increase in total particle volume. However, comparison of growth rate estimates from the Coulter Counter with those obtained radiochemically revealed poor agreement between the two methods. It is probable that the Coulter Counter is inaccurate in measuring the volume of cholesterol monohydrate crystals due to their anisometric shape.

Bile↗
PubMed1981

Precision and accuracy in the measurement of the cholesterol saturation index of duodenal bile. Lack of variation due to the menstrual cycle.

The reproducibility of measurement of the cholesterol saturation index of duodenal bile has been investigated in 5 healthy male and 10 healthy female volunteers. Two possible causes for variation in the saturation index were examined. First, the precision of the assays for cholesterol, bile acids, and phospholipids was such that after replicate analysis of eight individual bile samples, analytic variation produced cholesterol saturation index values which covered a mean range of 0.09 +/- 0.01 (SEM). Secondly, biologic variation was observed in all volunteers when eight duodenal bile samples were collected on different days over a 1-month period. Biologic plus analytic variation accounted for large fluctuations in the biliary cholesterol saturation index, covering a mean range of 0.32 +/- 0.05 (SEM). The magnitude of both types of variation was the same for men and women and was not related to physiologic changes in sex hormone levels during the menstrual cycle. After allowing for analytic variation, the cholesterol saturation index of duodenal bile accurately reflected that of gallbladder bile when collected at the same time from gallstone patients at operation.

Adult↗
PubMed1980

Chemical composition of gallstones resistant to dissolution therapy with chenodeoxycholic acid.

The gallstones of 14 patients, who had been treated unsuccessfully with chenodeoxycholic acid (15 mg/kg/day) for at lest six months, were obtained at cholecystectomy. The stones were then analysed for their cholesterol and calcium content. Two patients' stones were black in colour and low in cholesterol content, and were classified as pigment stones. Of the remaining 12 patients' stones, which all contained more than 70% cholesterol, 10 contained at lest 1% calcium on the stone surface. In two patients, the surface contained sufficient calcium to form a radio-opaque layer, although the stones had been radiolucent at the start of dissolution therapy. Overall, the results suggest that deposition of calcium salts inhibits the dissolution treatment of gallstones with chenodeoxycholic acid, irrespective of the radiolucency of the stones.

Adult↗
PubMed1979

Measurement of cholic acid synthesis and secretion by isolated rat hepatocytes.

Liver cells isolated from normal and cholestyramine-treated rats were incubated as cell suspensions for up to 4 hr in a simple, defined medium. The bile acid concentration in cells plus cell medium was determined by gas-liquid chromatography. Normal hepatocytes synthesized cholic acid at an initial rate of 0.25 nmol/mg cell protein per hr, which is comparable to rates reported from in vivo methods. This rate was increased more than 4-fold when rats were fed a cholestyramine-containing diet for 7 days prior to liver cell isolation. Although cholic acid was secreted into the cell medium during the incubation, it could not be assayed reliably by the hydroxysteroid dehydrogenase assay method, contrary to the reports of Anwer et al. 1975. Biochem. Biophys. Res. Commun. 64: 603 and Gardner and Chenouda 1978. J. Lipid Res. 19: 985.

Animals↗
PubMed1976

Synthesis of delta-aminolaevulinate synthase by isolated liver polyribosomes.

1. Postmitochondrial supernatants were prepared from the livers of chick embryos and were incubated under conditions that supported protein synthesis. delta-Aminolaevulinate synthase (EC 2.3.1.37) was synthesized by supernatants from livers treated with the porphyrinogenic drugs 2-allyl-2-isopropylacetamide and/or 3,5-diethoxycarbonyl-1,4-dihydrocollidine, but synthesis by supernatants from normal livers could not be detected. Synthesis of enzyme released from polyribosomes was measured by immunoprecipitation with specific antibody to the mitochondrial enzyme, and the specificity of the reaction was established by electrophoresis of dissociated immunoprecipitates on sodium dodecyl sulphate/polyacrylamide gels. 2. The relative synthesis of delta-aminolaevulinate synthase in vitro was comparable with that previously measured in vivo, and was correlated with the enzyme activity of the liver. 3. Enzyme synthesis in vitro occurred predominantly on free rather than membrane-bound polyribosomes. 4. The mol.wt. of the product synthesized in vitro was 7000 +/- 7000 by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. However, pulse-labelling of the enzyme in vivo confirmed its mol.wt. to be 49000 +/- 5000 when isolated from the mitochondrion. A small amount of immunoprecipitable enzyme of mol.wt. 70000 was detected in the cytosol in vivo. In chick embryo liver, delta-aminolaevulinate synthase therefore appears to be synthesized on cytoplasmic polyribosomes as a polypeptide of mol.wt. 70000, which in vivo is rapidly incorporated into the mitochondrion, and is then extracted as a lower-molecular-weight form. 5. Haemin added to the postmitochondrial supernatant-containing incubation mixture at concentrations up to 10 muM had no effect on general protein synthesis or the synthesis of delta-aminolaevulinate synthase. On the other hand, haemin treatment of induced chick embryo livers in vivo for 3h markedly decreased the relative synthesis of delta-aminolaevulinate synthase in vitro. These results suggest that haemin represses the synthesis of delta-aminolaevulinate synthase by decreasing the amount of mRNA for the enzyme available for translation.

5-Aminolevulinate Synthetase↗
PubMed1976

Delta-Aminolevulinic acid synthase from chick embryo liver mitochondria. I. Purification and some properties.

The purification of hepatic delta-aminolevulinic acid synthase (EC 2.3.1.37) was accomplished from chick embryo liver mitochondria, which had been treated with the combination of drugs, 2-allylisopropylacetamide and 1,4-dihydro-3,5-dicarbethoxycollidine to produce a high starting level of enzyme activity. After extraction from the mitochondria by sonication, the enzyme was purified to a final specific activity of over 10,000 nmol of aminolevulinate formed/30 min/mg of protein/37 degrees, using the techniques of Sephadex chromatography, ammonium sulfate fractionation, affinity chromatography for pyridoxal phosphate, and preparative isoelectric focusing. An isoelectric point of 7.0 and a molecular weight of 87,000 were obtained for the native enzyme. The subunit molecular weight of 49,000, obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggested it was a dimer. The enzyme was inhibited by p-chloromercuribenzoate and N-ethylmaleimide, stimulated by cations and exhibited an ultraviolet absorption spectrum characteristic of pyridoxal 5'-phosphate enzymes with absorption maxima at 325 and 420 nm.

5-Aminolevulinate Synthetase↗