Neuraminidase in pig gastric mucus

This paper demostrates the presence of neuraminidase (EC 3.2.1.18) in the isolated gastic mucoproteins, and indicates its probable origin from bacteria in the mucous secretion. The sialic acid content of gastric mucoproteins is discussed in terms of these findings.     

Functional interactions of gastric mucus glycoprotein

The concentration-dependence of viscosity in solutions of purified glycoprotein from pig gastric mucus is of the form expected for simple polymer entanglement. At higher concentrations, however, a weak viscoelastic gel is formed, whose mechanical spectrum (over the frequency range 10⁻²---10² rad s⁻¹) indicates a more stable mechanism of interchain association, and is closely similar to that of native mucus. On prolonged exposure to solvent, reconstituted gels redissolve, while native mucus retains its structural integrity (as characterized by the storage modulus, G′) but releases a significant, variable amount of glycoprotein. On proteolytic digestion or disulphide reduction of the glycoprotein to its component subunits, network structure is lost, but the mechanical spectra of the resulting solutions show interactions beyond simple entanglement. From this evidence we suggest that in the sub-micrometre-sized ‘domains’ in which native mucus is secreted, the carbohydrate side chains of component glycoprotein molecules are interdigitated in a comparatively stable arrangement, with the polymeric subunit structure of the glycoprotein conferring the branching required for development of a three-dimensional network, and with a substantial, variable sol-fraction of free glycoprotein within the interstices of the gel. On solubilization of native mucus, the ‘domain’ structure is destroyed irreversibly. Interaction between domains, and between individual molecules in gels reconstituted from the component glycoprotein after extraction and purification, is by more transient, non-specific interdigitation and entanglement, to confer the overall flow and spreading characteristics of the gel.     

Proteolysis of insoluble porcine gastric mucus

Gastric mucus of the pig (Sus scrofa L.) has been separated into two distinct components in guanidine:urea:phosphate. The insoluble gelatinous phase has been solubilized by reduction in bicarbonate buffer. Gel filtration chromatography suggests the presence of a high molecular weight (1.92 X 10(6] and a low molecular weight (6.25 X 10(5] mucoprotein. Proteolytic digestion with trypsin, papain and pronase yielded glycopeptides whose molecular weights ranged from 2.6 X 10(5) to 6.25 X 10(5). Amino acid analysis of each mucoprotein fragment was determined. Notable differences when compared to soluble mucus glycoproteins lie in the conservation of those amino acids likely to be involved in the O-glycosyl linkage.     

The gastric mucus layers: constituents and regulation of accumulation

The mucus layer continuously covering the gastric mucosa consists of a loosely adherent layer that can be easily removed by suction, leaving a firmly adherent mucus layer attached to the epithelium. These two layers exhibit different gastroprotective roles; therefore, individual regulation of thickness and mucin composition were studied. Mucus thickness was measured in vivo with micropipettes in anesthetized mice [isoflurane; C57BL/6, Muc1-/-, inducible nitric oxide synthase (iNOS)-/-, and neuronal NOS (nNOS)-/-] and rats (inactin) after surgical exposure of the gastric mucosa. The two mucus layers covering the gastric mucosa were differently regulated. Luminal administration of PGE(2) increased the thickness of both layers, whereas luminal NO stimulated only firmly adherent mucus accumulation. A new gastroprotective role for iNOS was indicated since iNOS-deficient mice had thinner firmly adherent mucus layers and a lower mucus accumulation rate, whereas nNOS did not appear to be involved in mucus secretion. Downregulation of gastric mucus accumulation was observed in Muc1-/- mice. Both the firmly and loosely adherent mucus layers consisted of Muc5ac mucins. In conclusion, this study showed that, even though both the two mucus layers covering the gastric mucosa consist of Muc5ac, they are differently regulated by luminal PGE(2) and NO. A new gastroprotective role for iNOS was indicated since iNOS-/- mice had a thinner firmly adherent mucus layer. In addition, a regulatory role of Muc1 was demonstrated since downregulation of gastric mucus accumulation was observed in Muc1-/- mice.     

The presence of polysaccharide in normal human gastric mucus.

Polysaccharide material was found in the proteolysis glycopolypeptide fraction from normal human gastric mucus. The polysaccharide was identified by carbohydrate and amino acid analyses, by elemental analysis and from its behaviour on density-gradient ultracentrifugation. The polysaccharide is polydisperse with a weight-average molecular mass of 300 000 Da. Over 85% of the polysaccharide consists of galactose, and this represents 26% of all the galactose present in the fractions after beta-elimination with reduction of the glycopolypeptide material.     

Manipulation of fertility in domestic animals

For many years artificial insemination has been widely used for the manipulation of fertility in farm animals and more recently methods for the synchronization of oestrous cycles, superovulation and embryo transplantation have been increasingly applied. These techniques now provide new opportunities for the manipulation of gametes and embryos which might further enhance reproductive potential through the production of embryos in vitro, their preservation by deep freezing, cloning from embryonic cells or genetic manipulation to increase fecundity.     

The pulmonary circulation of some domestic animals at high altitude

Pulmonary haemodynamics and the histology of the pulmonary vasculature have been studied at high altitude in the yak, in interbreeds between yaks and cattle, and in domestic goats and sheep indigenous to high altitudes together with crosses between them and low-altitude strains. Cattle at high altitude had a higher pulmonary arterial pressure than cattle at low altitude. The yak and two interbreeds with cattle (dzos and stols) had a low pulmonary arterial pressure compared with cattle, while the medial thickness of the small pulmonary arteries was less than would be expected in cattle, suggesting that the yak has a low capacity for hypoxic pulmonary vasoconstriction and that this characteristic is transmitted genetically. Goats and sheep showed haemodynamic evidence of a limited response of the pulmonary circulation to high altitude, but no evidence that the high altitude breeds had lost this response. There were no measurable differences in the thickness of the media of the small pulmonary arteries between high- and low-altitude breeds of goats and sheep. All these species showed prominent intimal protrusions of muscle into the pulmonary veins but no specific effect of high altitude in this respect.     

Climatic stress indices for domestic animals

Past attempts to devise an index of climatic stress are briefly reviewed, and a new Relative Strain Index (RSI) is proposed. RSI is the ratio between the evaporative cooling required to compensate for the heat stress, and the maximum evaporative cooling that the animal can provide by physiological means. RSI takes into account the air temperature, vapor pressure, air movement,and radiant heat exchange,as well as the metabolic rate and insulation provided by the animal's coat. Thè index can be used to predict the probable tolerance of animals of types that have been sufficiently well studied. It can also be used to estimate the relative tolerances of animals having different physiological capacities or metabolic rates, but otherwise comparable; and it can be used to predict the relative effectiveness of proposed environmental controls.

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Zusammenfassung Die früheren Versuche, einen Index für den Klima-Sbress auszuarbeiten,werden kurz beschrieben und ein neuer Relativer Belastungsindex (relative strain index — RSI) wird vorgeschlagen. RSI ist das Verhältnis zwischen der Verdunstungskälte, die zur Kompensation der Hitzebelastung benötigt wird, und der maximalen Verdunstungskälte des Tieres, die physiologisch möglich ist. RSI berücksichtigt die Lufttemperatur, den Dampfdruck, die Luftbewegung und den Strahlungswärmeaustausch, fernèr die Höhe des Stoffwechsels und die Wärmeisolation durch das Fell. Der Index kann benutzt werden, um die wahrscheinliche Toleranz der Typen von Tieren vorherzusagen, die in ausreichender Weise erforscht worden sind. Er kann ebenfalls dazu verwendet werden, die relativen Toleranzen von Tieren abzuschätzen,die verschiedene physiologische Fähigkeiten oder Stoffwechselraten haben,aber im übrigen vergleichbar sind. Schliesslich kann er bei der Vorhersage der relativen Wirksamkeit der beabsichtigten Kontrollen des Umweltmilieus benutzt werden.

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Resume Les essais antérieurs d'élaboration d'un Indice de Contrainte Thermique sont brièvement décrits et un indice nouveau, appelé Indice de Charge Relative (relative strain index = RSI) est proposé. Cet indice est le quotient de la déperdition calorique par évaporation nécessaire en vue de compenser la charge thermique,sur la déperdition calorique maxima par évaporation physiologiquement réalisable par un animal. Cet indice tient compte de la température de l'air,de la pression partielle de vapeur d'eau, de la vitesse de l'air et des échanges par rayonnement thermique,ainsi que de la production de chaleur métabolique et de l'isolement calorique par le pelage. L'index peut être utilisé pour prédire la tolérance probable à la chaleur, d'espèces animales dont les modalités de thermorégulation sont déjà suffisamment bien connues. Il peut être utilisé en outre pour évaluer la tolérance relative d'animaux différant par leurs niveaux métaboliques ou par leurs capacités physiologiques; il peut enfin être utilisé pour prédire l'efficacité relative de divers moyens d'agir sur les conditions thermiques ambiantes.

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Parts of this paper were presented during the Third International Biometeorological Congress,Pau,France, 1–7 September 1963.