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S Barnes

Publications and source records attributed to S Barnes.

At least 199 records · Page 11Linked to original sources
PubMed1986

Evidence for reflex adrenergic inhibition of acid secretion in the conscious rat.

In conscious gastric fistula rats, gastric distension with saline to a pressure of 7 cm caused a threefold reduction of basal gastric acid secretion. Distension with 6.25% peptone solution to the same pressure doubled basal acid secretion. The saline distension-induced inhibition was abolished by guanethidine and markedly reduced by propranolol; phentolamine was ineffective. The response to peptone was unaffected by guanethidine. The results suggest that in the rat, gastric distension at physiological pressures inhibits acid secretion by a beta-adrenergic reflex. The inhibition can be masked by concurrent chemical stimulation of the gastric mucosa by the digestion products of food.

Animals↗
PubMed1986

Comparative antiandrogenic potency of spironolactone and cimetidine: assessment by the chicken cockscomb topical bioassay.

Spironolactone and cimetidine are effective antiandrogens in vivo, although they differ by five orders of magnitude in affinity for androgen receptors in vitro. To explore this discrepancy, we directly compared the antiandrogenic potency of these two compounds in vivo using the chicken cockscomb topical bioassay. In this assay, the growth of the androgen sensitive cockscomb of immature chicks after stimulation by various doses of androgen (dihydrotestosterone 5, 20, or 100 micrograms/day sc) is inhibited by antiandrogens in cream vehicle applied topically to the cockscomb itself. At low levels of androgen stimulation (5 micrograms/day), 0.5% topical cimetidine produced maximal suppression of cockscomb growth, while at high levels of androgen stimulation 100 micrograms/day), topical cimetidine in concentrations as high as 4% did not suppress cockscomb growth. In contrast, topical spironolactone in concentrations as low as 0.06% produced maximal inhibition of cockscomb growth at all androgen doses. Using an intermediate androgen dose (20 micrograms/day), the minimally effective antiandrogenic concentration of topical cimetidine was between 0.5 and 1.0%, while that for topical spironolactone was less than 0.001%. We conclude that the chicken cockscomb topical bioassay is a useful method for assessing relative potency of antiandrogens. With this method, spironolactone appears to be at least 500 times as strong an antiandrogen in vivo as cimetidine.

Administration, Topical↗
PubMed1986

Evidence for an ordered reaction mechanism for bile salt: 3'phosphoadenosine-5'-phosphosulfate: sulfotransferase from rhesus monkey liver that catalyzes the sulfation of the hepatotoxin glycolithocholate.

The in vivo formation of the sulfate ester of glycolithocholate is a critical step in the elimination of this hepatotoxic bile salt. Rhesus monkeys fed chenodeoxycholate or ursodeoxycholate, the precursors of lithocholate, develop frank cirrhosis in association with accumulation of nonsulfated glycolithocholate in bile. An enzyme catalyzing the formation of glycolithocholate-3-sulfate has been isolated from hepatic cytosol of adult female rhesus monkeys and has been purified 146-fold. When reduced it appears as a 30 kD band on an SDS-polyacrylamide gradient gel. It has a pH optimum of 7.0 and is stimulated by low concentrations of Mg2+ (up to 2 mM), but does not have an absolute requirement for this metal ion. The kinetics of this enzyme have been investigated to ascertain whether its reaction mechanism can account for the poor in vivo rate of glycolithocholate sulfation. Inhibitor studies with an oxidized metabolite of lithocholate, 3-keto-5 beta-cholanoate, showed that the latter is a competitive inhibitor of glycolithocholate and is noncompetitive with the active form of sulfate, 3'phosphoadenosine-5'-phosphosulfate. The monophosphonucleotide 3'-AMP is a competitive inhibitor of 3'phosphoadenosine-5'-phosphosulfate, and is noncompetitive with glycolithocholate. These observations are consistent with a sequentially ordered Bi Bi reaction mechanism in which the bile salt is the first substrate to bind to the enzyme. Such a reaction mechanism for bile salt:3'phosphoadenosine-5'-phosphosulfate:sulfotransferase would be, therefore, the first time in which the sulfate acceptor (the bile salt) is the initial substrate to bind to a sulfotransferase. These studies have shown that although rhesus monkeys have a liver enzyme capable of forming the sulfate ester of glycolithocholate, its reaction mechanism and the potent inhibition caused by simple metabolites, such as 3-keto-5 beta-cholanoate, may serve to under-express the activity of the enzyme in vivo.

Animals↗
PubMed1985

Mechanisms of T-cell functional deficiency in the acquired immunodeficiency syndrome.

Cell-mediated immune responses to cytomegalovirus infections were studied to define mechanisms for deficient effector T-cell responses in patients with the acquired immunodeficiency syndrome (AIDS). Progressive cytomegalovirus infection is common in such patients and is accompanied by a failure to develop HLA-restricted cytotoxic T-cell responses. The mechanism for the cytotoxic T-cell deficiency is presumably the basis for susceptibility to opportunistic infections. Precursors to these effector cells circulate in the peripheral blood of patients, but maturation of these cells into cytotoxic T cells is arrested during an interleukin-2-dependent phase. Production of interleukin-2 by lymphocytes from patients with AIDS is deficient because sera from these patients contain an inhibitor of interleukin-2 production. Excess suppressor cell activity does not appear to account for this deficient production. Studies of the source of the serum inhibitor should provide insights into the pathogenesis of AIDS and possible leads for effective treatment.

Acquired Immunodeficiency Syndrome↗
PubMed1985

Nuclear magnetic resonance spectroscopy of bile acids. Development of two-dimensional NMR methods for the elucidation of proton resonance assignments for five common hydroxylated bile acids, and their parent bile acid, 5 beta-cholanoic acid.

The complete 1H nuclear magnetic resonance assignments have been made for the common mono-, di-, and trihydroxy 5 beta-cholanoic acids; lithocholic acid, chenodeoxycholic acid, ursodeoxycholic acid, deoxycholic acid, cholic acid, and the unsubstituted parent compound, 5 beta-cholanoic acid, by heteronuclear-correlated two-dimensional NMR. The known 13C chemical shifts of these compounds were used to make the proton resonance assignments, and consistency of the carbon and proton assignments was verified by expected changes due to substituent effects. This has led to clarification of previously published 13C NMR resonance assignments. Addition of the 3 alpha, 7 alpha, and 12 alpha hydroxyl substituent effects derived from the mono- and dihydroxycholanoic acids yielded predicted values for proton chemical shifts of the trihydroxy-substituted 5 beta-cholanoic acid, cholic acid, that agreed well with experimental values. It is suggested that the individual substituent effects can be used to predict proton chemical shifts for hydroxycholanic acids containing other combinations of 3 alpha, 7 alpha, 7 beta, and 12 alpha hydroxyl groups.

Bile Acids and Salts↗
PubMed1984

Autonomous cholesterol biosynthesis in murine hepatoma. A receptor defect with normal coated pits.

These studies indicate that autonomous cholesterol biosynthesis by hepatocellular carcinoma may result from absent or defective receptors for chylomicron remnants on the surface of the malignant hepatocytes. In vivo, DAB2 hepatoma or liver were perfused with chylomicron remnants labeled with tritiated palmitic acid. Normal liver had chylomicron remnant uptake/gm tissue that was ten times that of hepatoma. In vitro studies using isolated hepatocytes and cultured DAB2 hepatoma cells showed similar results. Uptake of chylomicron remnants labeled with 3H-palmitic acid by normal hepatocytes during a 4-hour period was ten times that of hepatoma cells. Both in vivo and in vitro differences were statistically highly significant (P less than 0.005). Since many surface receptors are related to the coated pits, the cellular membranes of both neoplastic and normal liver cells were examined by electron microscopy. Coated pits were present in both the hepatoma and normal liver cells and occupied 2.61% and 2.65% of the cell surface, respectively. The defective uptake of chylomicron remnants by DAB2 hepatoma appears to be related to the chylomicron remnant receptor and not to the coated pit-internalization mechanism.

Animals↗
PubMed1984

Aggregation patterns of bile salts: crystal structure of calcium cholate chloride heptahydrate.

Crystals of calcium cholate chloride heptahydrate, CaC24H39O7Cl . 7H2O, are monoclinic, space group P2(1), with a = 11.918(2), b = 8.636(1), c = 15.302(3) A, beta = 97.93(3) degrees, V = 1559.9(8) A3, and Z = 2. A trial structure was obtained by Patterson and Fourier techniques and was refined by full-matrix least-squares calculations using absorption corrected CuK-alpha diffractometer data. The final R index is 0.047. The crystal structure contains bilayer-type arrangements, with hydrophobic portions of cholate rings sandwiched between layers of polar groups that are interacting with calcium ions and water molecules. The calcium ion is coordinated to five water molecules and to the two carboxylate oxygen atoms of the cholate residue. Two additional water molecules are involved only in crystal packing through the formation of hydrogen bonds. Cholate-cholate hydrophobic interactions involve contacts between the hydrocarbon portions of the carboxylate sidechains and the A and B rings. This results in a staggered packing pattern that is nearly identical to that found in crystals of sodium cholate and rubidium deoxycholate. Similar bilayer aggregation patterns may also be involved in the formation of bile salt micelles in aqueous media. The characteristic bilayer packing arrangement can accommodate a variety of cation-binding patterns, as evidenced by the finding that calcium, sodium, and rubidium ions interact with the polar faces of the bilayers in different ways. The carboxylate sidechain displays two different conformations in the crystal structure of calcium cholate chloride heptahydrate. Variation in sidechain conformation may be of importance in the adjustment required to accommodate different cation coordination schemes.

Bile Acids and Salts↗
PubMed1983

Alkaline butanol extraction of bile salt and steroid sulfate esters: application to the assay of sulfotransferases.

A butan-1-ol solvent-extraction procedure has been evaluated for the assay of 3'-phosphoadenosine-5'-phosphosulfate:sulfotransferase activity with various bile salt and steroid substrates. Although butanol extracted the sulfate esters of steroids and bile salts from aqueous solution at neutral pH, extraction at basic pH gave optimum recovery which was independent of protein in the sample. Greater than 99.9% of unreacted 3'-phosphoadenosine-5'-phospho[35S]sulfate remained in the aqueous phase. The data for sulfotransferase activities obtained with this solvent-extraction assay were not significantly different from those obtained with a standard thin-layer chromatography method. Solvent extraction has enabled multiple, rapid assays of several steroid and bile salt sulfotransferases during chromatographic purification of these enzymes from tissue fractions.

1-Butanol↗
PubMed1982

Evidence for heterogeneity of hepatic bile salt sulfotransferases in female hamsters and rats.

Gel filtration and anion-exchange chromatography have been used to investigate whether 3'-phosphoadenylylsulfate:bile salt sulfotransferase activity from female rat and hamster liver is heterogeneous. Using these techniques at least three different enzyme activities were demonstrated with two different bile salt substrates. In both animals, but particularly the rat, there was a marked difference in the substrate specificity between each of the peaks of enzyme activity. The reducing agent, 2-mercaptoethanol, enhanced the proportion of the highest molecular weight (130 000) form of the enzyme from rat liver detected with glycochenodeoxycholate as substrate. This effect was duplicated by alkylation of sulfhydryl groups with iodoacetamide and is interpreted as being due to intermolecular association caused by disruption of intramolecular disulfide bonds.

Alkylation↗
PubMed1982

High resolution nuclear magnetic resonance spectroscopy of bile salts: individual proton assignments for sodium cholate in aqueous solution at 400 MHz.

The 400 MHz 1H-nuclear magnetic resonance spectrum of sodium cholate in dilute aqueous solution has been successfully resolved using a combination of decoupling, partial relaxation, and decoupled partial relaxation techniques. The individual carbon resonances in the 13C-NMR spectrum of sodium cholate have also have assigned. Assignments of individual methylene protons were made by consideration of the molecular structure of sodium cholate and the expected couplings and 1H-nuclear Overhauser enhancement experiments. Verification of the assignments of the methine protons was made by application of single frequency 1H-decoupled 13C-NMR. Variation of pH* from 6.0 to 11.0 did not alter the individual chemical shifts except for those between 2.12 delta and 2.30 delta, originating from the protons on the C23 position adjacent to the ionizable carboxyl group. The chemical shifts of the proton resonances were independent of concentration below 5 mM. Above 10 mM (micellar region), the proton chemical shifts were altered slightly and some band broadening occurred. These data are consistent with the formation of small micellar aggregates (up to N = 4) of cholate molecules.

Bile Acids and Salts↗