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M J Armstrong

Publications and source records attributed to M J Armstrong.

52 records · Page 3Linked to original sources
PubMed1982

Biliary lipids in New World monkeys: dietary cholesterol, fat, and species interactions.

The separate effects contributed by dietary cholesterol and dietary fat on several parameters of biliary lipid metabolism thought to be important in the genesis of cholesterol gallstones were examined in squirrel and cebus monkeys fed diets containing either corn or coconut oil from birth. Half the monkeys were also fed cholesterol. In gallstone-susceptible squirrel monkeys, corn oil tended to decrease the bile acid pool size and decrease the percentage of taurochenodeoxycholic acid. Dietary cholesterol effected major changes in gallbladder bile molar percent lipid composition with significantly increased cholesterol saturation indices that exceeded the metastable-labile limits. The supersaturated biles notwithstanding, none of the monkeys developed gallstones and only one had cholesterol crystals in its bile. By contrast, the gallstone-resistant cebus monkeys experienced less remarkable shifts in biliary lipid composition during dietary challenges of cholesterol and fat. The data are consistent with the hypothesis that neither a diminished bile acid pool size nor bile supersaturated with cholesterol are sufficient in themselves to result in gallstone formation in immature monkeys.

Animals↗
PubMed1982

The hydrophobic-hydrophilic balance of bile salts. Inverse correlation between reverse-phase high performance liquid chromatographic mobilities and micellar cholesterol-solubilizing capacities.

To examine quantitatively the hydrophobic-hydrophilic properties of bile salts, we determined the reverse-phase high performance liquid chromatographic (HPLC) mobilities of monomeric bile salt solutions and the equilibrium cholesterol-solubilizing capacities of 100 mM micellar solutions. Studies with the common bile salts (ursodeoxycholate, UDC, cholate, C, chenodeoxycholate, CDC, and deoxycholate, DC) demonstrated that HPLC mobility, which correlates with hydrophilicity, was markedly influenced by both position and orientation, in addition to number, of hydroxyl functions, in that mobility decreased in the order UDC > C > CDC > DC. Conjugation of the bile salt was also important, in that the HPLC mobility of the taurine (T)-conjugates was greater than the glycine (G)-conjugates which in turn was greater than that of the free bile salts. Equilibrium micellar cholesterol solubilities were also influenced by bile salt structure and correlated inversely with hydrophilicity, in that solubility decreased in the order DC > CDC > C > UDC with free bile salts > G-conjugates > T conjugates. For each bile salt series, double logarithmic plots of the cholesterol-solubilizing capacities expressed in mole fraction units versus the HPLC retention factors (k') gave linear relationships. Linear regression equations were employed to predict the equilibrium cholesterol-solubilizing capacities of a number of less common bile salts from their HPLC retention factors. Each theoretical value agreed closely with that derived entirely by experiment. A comparison of the HPLC mobilities of the less common bile salts with the more common species revealed that not only were sulfate and oxo substituents more hydrophilic than alpha-oriented hydroxyl functions, but, in the dihydroxy species, a single equatorial hydroxyl function such as in UDC (3alpha,7beta) and in hyodeoxycholate (3alpha,6alpha) was more hydrophilic than two or three hydroxyl functions at 3, 7, and/or 12alpha (axial) positions. These studies taken together suggest that reverse-phase HPLC mobility and equilibrium cholesterol-solubilizing capacities are inverse functions of each other and correlate closely with the hydrophilicity of bile salt molecules. In addition, the evidence here deduced further strengthens our recent deductions based on an evaluation of a number of other physical-chemical properties (Carey, M. C., J-C. Montet, M. C. Phillips, M. J. Armstrong, and N. A. Mazer, 1981. Biochemistry. 20: 3637-3648.) that cholesterol may be solubilized in micellar bile salt solutions by both hydrophobic and hydrophilic association with the external ("hydrophilic") surface of bile salt micelles rather than with the hydrophobic surface of the micelle's interior.-Armstrong, M. J., and M. C. Carey. The hydrophobic-hydrophilic balance of bile salts. Inverse correlation between reverse-phase high performance liquid chromatographic mobilities and micellar cholesterol-solubilizing capacities.

Bile Acids and Salts↗
PubMed1981

Thermodynamic and molecular basis for dissimilar cholesterol-solubilizing capacities by micellar solutions of bile salts: cases of sodium chenodeoxycholate and sodium ursodeoxycholate and their glycine and taurine conjugates.

The bile salts chenodeoxycholate (CDC) and its 7 beta-hydroxy epimer ursodeoxycholate (UDC) are administered therapeutically (as acids) to dissolve cholesterol gallstones in man. Since their micellarr solutions and those of their physiological conjugates differ strikingly in their capacities to solubilize cholesterol, we studied the interfacial and micellar properties of the epimers by a number of complimentary physical--chemical methods and correlated these with their solubilizing capacities. The critical micella concentrations (cmc) estimated by surface tension, dye titration, and turbidimetry were similar (1-5 mM), varying slightly with the bile salt species, the method employed, NaCl concentration (0-1 M), and temperature (10-50 degrees C). The weight-average aggregation number (number of monomers per micelle, nw) at the cmc, derived from Debye plots of conventional light-scattering data and from the mean hydrodynamic radii of the micelles obtained by quasi-elastic light-scattering spectroscopy, revealed no appreciable differences between the UDC-CDC epimers or between their conjugates. From the mean hydrodynamic radii, the taurine conjugates were found to form larger micelles (nw = 15-17) than the glycine conjugates (nw = 13) which in turn were larger than the free species (n w = 5), respectively. Consistent with previous experimental deductions, free and conjugated CDC micelles grew slightly in size with increases in total lipid concentration, but UDC micelles did not. With solubilization of cholesterol monohydrate, the mean sizes of UDC (13.4 A) and of CDC (13 A) micelles in 10 g/dL solutions did not change appreciably, even as the cholesterol saturation limit was reached. At the air-5 M NaCl (pH 2) interface, the glycine conjugates formed more expanded monomolecular films than the free acid, and both UDC and its glycine conjugate collapsed at surface pressures that were 10-20 mN m-1 lower than the collapse pressures of monolayers of CDC and its glycine conjugate. Similarly, adsorbed monolayers of ionized UDC and its taurine conjugate lowered the surface tension of water approximately 5 mN m-1 less than equimolar concentrations of CDC and its taurine conjugate. By employing high-performance reversed-phase liquid chromatography (HPLC), we measured the relative hydrophilic--hydrophobic properties of the bile salts and found a close correlation between HPLC mobility and cholesterol-solubilizing cpacity. Assuming a single cholesterol binding site per micelle, we estimated from the nw values and bile salt/cholesterol saturation ratios that the magnitude of the cholesterol binding constant (K) was 5.7 X 10(6) L/mol for unconjugated CDC and 2.5 X 10(5) L/mol for unconjugated UDC at 30 degrees C. These results suggest that the differences in cholesterol-solubilizing capacities of CDC and UDC and their conjugates are due to subtle differences in micellar structure, resulting from the axial or equatorial orientation of the 7-hydroxyl function and the various conjugating groups...

Chenodeoxycholic Acid↗
PubMed1981

Bile lipid alterations in taurine-depleted monkeys.

Newborn cebus and cynomolgus monkeys, differing in their inherent taurine-glycine conjugation of bile acids, were fed taurine-free soy protein infant formula (Isomil) with or without added taurine (500 mg/kg dry diet). After 5 months, monkeys were anesthetized, their enterohepatic circulation interrupted, and their bile pool drained for 4.5 h. Bile acid conjugation, total bile acid pool size, biliary lipid composition, and theoretical maximal cholesterol solubility in bile were determined. Taurine depletion in cebus monkey, an obligate taurine conjugator (97%), did not reduce bile acid conjugation with taurine, or did it alter bile acid pool size, biliary lipid composition, or theoretical maximal cholesterol solubility in bile. Conversely, taurine depletion in cynomolgus, a species normally conjugating with some glycine (15 to 20%), significantly reduced conjugation of taurine with bile acids from 84 to 64%, essentially doubling that of glycine from 16 to 36%. Furthermore, theoretical maximal cholesterol solubility in cynomolgus bile improved significantly as a result of taurine depletion. This improvement was associated with increased percentage distribution of biliary phospholipid from 17 to 33%, in turn reflecting an increase in the taurochenodeoxycholate to taurocholate ratio from 0.7 to 2.9. Concomitant increase in biliary cholesterol concentration associated with increased glycine conjugation precluded any changes in the percent saturation of bile which remained constant at 130% for both dietary groups of cynomolgus. Taurochenodeoxycholate uniquely conserved taurine in the face of body taurine depletion. Taurine availability thus potentially has a substantial influence on bile acid characteristics and cholesterol solubility in a glycine conjugating primate.

Animals↗
PubMed1980

Nitrate uptake by roots as regulated by nitrate assimilation in the shoot of castor oil plants.

Ricinus communis was used to test the Ben Zioni-Dijkshoorn hypothesis that NO(3) uptake by roots can be regulated by NO(3) assimilation in the shoot. The rate of the anion charge from assimilated NO(3) (-) (and SO(4) (2-)) was followed in its distribution between organic acid anion accumulation and HCO(3) (-) efflux into the nutrient solution. In plants adequately supplied with NO(3) (-), HCO(3) (-) efflux accounted for between 56 and 63% of the anion charge. When the plants were subjected to a low NO(3) regime HCO(3) (-) excretion accounted for only 23% of the charge. A comparison of mature plants growing for a 10-day period at the two levels of NO(3) nutrition revealed that the uptake of NO(3) (-) at the higher level was increased 3-fold, whereas K uptake was unaltered. To trace ion movement within the plant, the ionic constituents of xylem and phloem sap were determined. In xylem sap these constituents were found to be predominantly K(+), Ca(2+), and NO(3) (-), whereas in the phloem sap they were mainly K(+) and organic acid anions. Results have been obtained which may be interpreted as providing direct evidence of NO(3) uptake by roots regulated by NO(3) reduction in the tops, the process being facilitated by the recirculation of K(+) in the plant.

Journal Article↗
PubMed1979

Estimation of potassium recirculation in tomato plants by comparison of the rates of potassium and calcium accumulation in the tops with their fluxes in the xylem stream.

A procedure to estimate the extent of K recirculation in plants is proposed. This is based on the ratio of the upward fluxes of K to Ca in the xylem sap from root to shoot with the ratio of K to Ca accumulation in plant tops.In a preliminary investigation the factors influencing the K to Ca ratio in the xylem sap were considered. Tomato plants were grown at three levels of K nutrition and harvested at different times during the 24-hour day period. It was shown that the K to Ca ratio in xylem sap changed dramatically depending on the time of sap collection after decapitation, the values falling from over 2 to less than unity over the 4-hour period of collection. Diurnal effects on exudation were less marked but also of significance. The level of K nutrition was of little importance. It is suggested that a representative xylem sap from tomato plants can best be obtained from samples taken between 15 and 60 minutes after decapitation.In a second experiment K recirculation was estimated. At nine harvesting stages over a 24-hour period the K to Ca ratio in the xylem sap was invariably higher than the K to Ca ratio of accumulation in the tops over the same period. From this information it was calculated that about 20% of the upward flux of K in the xylem stream resulted from recirculated K.

Journal Article↗
PubMed1976

Billiary lecithin secretion. II. Effects of dietary choline and biliary lecithin synthesis.

Choline which is absorbed from the intestine isne produced no change in bile salt pool size or secretion rate. However, with each increment in dietary choline, biliary lecithin as well as cholesterol secretion rates were significantly increased. The results demonstrate that although bile salt is required for biliary lecithin secretion, the magnitude of secretion is principally dependent upon the extent of biliary lecithin synthesis, which in turn may be regulated by the amount of dietary choline. Results further indicate that biliary cholesterol secretion is more closely linked to lecithin than to bile salt secretion. These findings would therefore suggest that lecithin secretion might be independently manipulated when bile salt is deficient to achieve enhanced biliary cholesterol transport.

Animal Nutritional Physiological Phenomena↗
PubMed1975

Raised alpha-fetoprotein levels in amniotic fluid and maternal serum in a triplet pregnancy in which one fetus had an omphalocoele.

During the second pregnancy of a 31-year-old patient, who already had a child with hydrocephalus, the ultrasonic scan at 16 weeks gestation demonstrated the possiblity of triplets. Raised amniotic fluid and maternal serum alpha-fetoprotein concentrations were observed at 16 and 17 weeks gestation. The pregnancy was terminated at 17 weeks gestation and one of the fetuses had an extensive omphalocoele, radial aplasia and digital abnormalities.

Abnormalities, Multiple↗
PubMedDate not supplied

Inhibition of neurotensin release by a cyclic hexapeptide analog of somatostatin.

Studies were performed to determine whether the cyclic hexapeptide analog of somatostatin, cyclo(N-Me-Ala-Tyr-D-Trp-Lys-Val-Phe) II, could alter circulating levels of neurotensin (NT) and inhibit the release of NT from small intestine following the intraluminal perfusion of lipid and ETOH. The small intestine of anesthetized rats was perfused with 0.9% NaCl, 1mM ETOH, 100 mM ETOH or 1 mM oleic acid with and without the intravenous infusion of the somatostatin analog. Plasma samples collected from the superior mesenteric vein were extracted, chromatographed on HPLC and assayed with both C-terminal and N-terminal antisera to NT. The basal circulating levels of chromatographically and immunochemically identified NT observed during the perfusion of the small intestine with 0.9% NaCl were significantly lower (p less than 0.01) during the IV infusion of the somatostatin analog as compared to animals infused IV with saline. The 2-3 fold increase in plasma levels of NT observed with the intestinal perfusion of oleic acid and ETOH did not occur in animals simultaneously infused IV with the somatostatin analog. The somatostatin analog was also effective in decreasing the basal levels of NT metabolite NT(1-8) as well as inhibiting the increase in this metabolite that accompanies the stimulated release of NT.

Animals↗
PubMedDate not supplied

Comparison of motility and membrane integrity to assess rat sperm viability.

Rat sperm motility and membrane integrity were compared as endpoints for viability. Sperm motility was measured by computer-assisted semen analysis (CASA), whereas membrane integrity was assessed by flow cytometric analysis of sperm stained with two nucleic acid stains, SYBR-14 and propidium iodide. The two techniques were compared in experiments that examined sperm viability over time and by analysis of known mixtures of control and freeze/thaw-killed sperm. Results from the two approaches were quantitatively very similar. Sperm from rats treated with dibromoacetic acid (600 or 1200 mg/kg) or alpha-chlorhyrin (100 mg/kg) were also analyzed. Neither technique detected a treatment-related effect with dibromoacetic acid. CASA identified a significant decrease in sperm motility in alpha-chlorhyrin-treated rats, whereas flow cytometric analysis did not find a measureable change in sperm membrane integrity. Because decreases in sperm motility would be expected to directly affect fertility, CASA may be a more robust endpoint for risk assessment in reproductive toxicology studies than flow cytometric analysis of membrane integrity.

Acetates↗