Regulation of gallbladder cholesterol concentration in the hamster. Role of hepatic cholesterol level

The goal of this investigation was to determine how alterations in hepatic cholesterol metabolism influence the cholesterol content of gallbladder bile in hamsters. Although the rate of hepatic cholesterol synthesis was varied over 600-fold, there was no direct relationship between the rate of cholesterol synthesis and the cholesterol content of gallbladder bile. However, expansion of the hepatic cholesterol pool by 42-fold resulted in an 11-fold increase in gallbladder bile cholesterol. Examination of four subfractions of the hepatic cholesterol pool revealed that the cholesterol content of gallbladder bile was most consistently correlated with the free cholesterol level in both hepatic tissue and hepatic microsomes from all experimental groups. In most groups of animals in which gallbladder bile cholesterol was increased, plasma lipoprotein cholesterol levels were also increased. It was concluded that in hamsters, under these experimental conditions, changes in the cholesterol content of gallbladder bile were directly related to alterations in cholesterol content of the liver and most closely related to alterations in the free cholesterol content of that tissue.     

Comparative rates of transfer of N-acetylneuraminic acid to acceptors bearing one or more Gal(beta 1-4)GlcNAc terminus by the Gal(beta 1-4)GlcNAc(NeuAc-Gal) (alpha 2-6)-sialyltransferase from embryonic chicken liver. Utilization of oligosaccharides as acceptors in sialyltransferase assays.

Using a number of branched and unbranched oligosaccharides, glycoproteins and artificial glycoproteins bearing Gal(beta 1-4)GlcNAc-R termini as acceptors (where R represents H, oligosaccharide, oligosaccharide-protein or fatty acid-protein), the comparative rates of transfer of NeuAc by the Gal(beta 1-4)GlcNAc(NeuAc-Gal) (alpha 2-6)-sialyltransferase of embryonic chicken liver were determined. Acceptor substrates were utilized at levels approximating physiological, near the Km value of the best acceptor, desialylated alpha 1 acid glycoprotein. The sialyltransferase has a marked preference for multi-branched acceptors. From the specificity data, it is concluded that the enzyme binds at least two Gal(beta 1-4)GlcNAc termini of an acceptor molecule, and that the relative orientation of the branches is an important factor determining the rate of catalysis by the enzyme. The use of oligosaccharides as acceptors to study sialyltransferase catalyses is emphasized. Results are discussed in the context of the mode of assembly of sialoside termini of known glycoprotein structures in vivo.     

Tryptophan and glucose metabolism in rat liver cells. The effects of DL-6-chlorotryptophan, 4-chloro-3-hydroxyanthranilate and pyrazinamide.

Liver cells pre-incubated with 1 mM-DL-6-chlorotryptophan are less sensitive to tryptophan-mediated inhibition of gluconeogenesis; this effect is apparent both at physiological (0.1 mM) and higher (0.5 mM) concentrations of tryptophan. 4-Chloro-3-hydroxyanthranilate (1-100 microM) has effects similar to those of DL-6-chlorotryptophan. The effects of both compounds are consistent with a decrease in quinolinate formation, a consequence of inhibition of 3-hydroxyanthranilate oxidase. Pyrazinamide (0.25-5.0 mM) significantly decreased flux through the glutarate pathway and potentiated tryptophan-mediated inhibition of gluconeogenesis; these changes were apparent at physiological concentrations of tryptophan. The effects of pyrazinamide are consistent with an increase in quinolinate formation resulting from inhibition of picolinate carboxylase.     

Effect of host density on searching behaviour of Nemeritis canescens (Hymenoptera: Ichneumonidae)

Observations were made over one hour of individual parasites, N. canescens, searching for their hosts, larvae of the moth Plodia interpunctella, at five different host densities. Records were made of the total number of hosts encountered at each density, the total number of eggs laid and the handling time per host.Holling's disc equation was found to fit the data well and gave estimates for rate of parasite search (a) and handling time (b) close to values actually observed. Despite the good fit, rate of search and handling time both declined as host density increased. The time spent handling already parasitised hosts, avoidance time was found to be about half the value of handling time.

---

Resume Les observations ont été faites durant une heure sur des parasites isolés, N. canescens, prospectant des lots de chenilles de Plodia interpunctella — leurs hôtes — à cinq densités différentes. Pour chaque densité, ont été notés: le nombre total d'hôtes rencontrés, le nombre total d'ufs pondus et le temps d'examen par hôte.L'équation de Holling s'est bien adaptée aux données et a fourni des estimations pour le taux de prospection des parasites (a) et le temps d'examen (b) proches des valuers réellement observées. Malgré une bonne adaptation, le taux de prospection et le temps d'examen diminuent tous deux quand la densité de l'hôte augmente. Le temps dépensé à l'examen des hôtes déjà parasités, temps de rejet correspond à environ la moitié du temps d'examen.

     

The expression in E. coli of synthetic repeating polymeric genes coding for poly(L-aspartyl-L-phenylalanine)

Two dodecadeoxynucleotides of defined sequence have been synthesised by phosphotriester methodology. They can be polymerised to give a double stranded DNA which codes, when read in the correct phase, for the repeating dipeptide poly(aspartyl-phenylalanine). This polymeric DNA has been cloned in E. coli K12 using as vector a plasmid having a controllable bacterial promoter upstream of the insertion site. Clones containing genes coding for up to 150 repeats of (aspartyl-phenylalanine) have been isolated and characterised. The polymeric inserts appear to be stable over many generations and are expressed in E. coli under the control of the bacterial promoter, to give a polymer of phenylalanine and aspartic acid which may be broken down enzymically to yield aspartyl-phenylalanine.     

Mycardial histone acetylation

Myocardial histone acetylation was investigated in an isolated perfused heart preparation. Radioactive acetate rapidly accumulated in the intracellular compartment which preceded the covalent modification of histones. The acetylation of nucleohistones was rapid and reached a maximum during the first 20 min of perfusion. After 60 min of continuous perfusion there was a three-fold decrease in the amount of acetate bound to histone proteins. Histone H3 appeared to be preferred substrate for acetylation and was most responsive to a change in the concentration of radioactive acetate as well as the perfusion time.     

Activity of homocarnosine and other compounds against staphylococcal infections in mice

Homocarnosine and carnosine have been identified in bovine brain extracts which are effective in protecting mice against infections by Staphylococcus aureus. These peptides, as well as l-1-methylhistidine, beta-alanine, gamma-aminobutyric acid, delta-aminovaleric acid, epsilon-aminocaproic acid, 1-aminomethylcyclohexane-4-carboxylic acid, and anserine, were tested as prophylactic agents against S. aureus infections in C3H and Swiss mice. Histidine and methylhistidine were ineffective in preventing mortality in both mouse strains. Carnosine, anserine, and epsilon-aminocaproic acid were effective in C3H but not in Swiss mice. beta-Alanine and gamma-aminobutyric acid were weakly effective (C3H) or ineffective (Swiss). delta-Aminovaleric and 1-aminomethylcyclohexane-4-carboxylic acid (tested only in Swiss) were somewhat effective in early stages of the infection. Homocarnosine was the best compound and was highly effective in protecting both mouse strains against S. aureus infections by the testing procedure employed.     

Microbial Contamination on Disposable Hypodermic Syringes Prior to Sterilization by Ionizing Radiation

A large number of syringes were taken from the production lines of three independent manufacturers; the numbers and types of microorganisms contaminating these randomly sampled syringes were assessed in the laboratories maintained by each of these manufacturers for routine sterility testing, according to a standard protocol devised by the Research Committee of the UK Panel on Gamma and Electron Irradiation, which coordinated the investigation and analyzed the results. Items produced by a manufacturer were assessed for microbiological contamination both in their own laboratories and in the laboratories of the other manufacturers. The level of “false-positive” results was determined independently for each laboratory by the testing of “known sterile” items which had been subjected to the radiation-sterilization process. Both the percentage of syringes initially sterile and the average number of organisms per contaminated syringe differed among the three manufacturers. When corrected for interlaboratory differences, the number of syringes initially sterile ranged from 16 to 48%, and the mean number of organisms per contaminated syringe was 20 to 70. Of 964 syringes tested by all three laboratories, only one contained over 1,000 aerobic organisms (1,133). The most common organisms found were coagulase-negative, gram-positive cocci. Two manufacturers assessed contamination by anaerobic organisms; of 610 syringes, 1 contained 4,275 organisms and 3 more had 100 to 1,000 organisms, but 488 (80%) were uncontaminated by anaerobes. The results are discussed in the context of the choice of radiation dose necessary for the sterilization of medical products manufactured under controlled hygienic conditions.     

The stereochemistry of hydrogen elimination from C-7 during biosynthesis of ecdysones in insects and plants

1. [7alpha-(3)H(1)]- and [7beta-(3)H(1)]-Cholesterol were synthesized by a modified method. 2. The stereochemistry of Delta(7)-bond formation during ecdysone and ecdysterone biosynthesis in the insect, Calliphora erythrocephala and the plants, Taxus baccata and Polypodium vulgare was investigated by using [4-(14)C,7alpha-(3)H(1)]cholesterol and [4-(14)C,7beta-(3)H(1)]cholesterol. 3. In each case, the 7beta hydrogen was stereospecifically eliminated. 4. The possible significance of the results is discussed in relation to double-bond formation in other systems and the stage at which the Delta(7) bond is introduced during ecdysone biosynthesis.