Gastric mucosubstances

Use of highly alkaline solution, such as bicarbonates, causes excessive liquefaction of mucus, due to depolymerization of mucosubstances and to potentiation of the activity of mucolysin at this pH. This would result, unavoidably, in changing the composition of gastric mucosubstances. 

Other workers determined the entire carbohydrate spectrum of human gastric juice in an attempt to evaluate the composition of gastric mucosubstances. Richmond et al. (R4) and Hoskins and Zamcheck (H50) studied a large number of individual gastric juices in our laboratory (G55) a large pool of normal gastric juices was studied for hexoses, hexosamine, fucose, sialic acid, uronic acid, and total carbohydrate content. Results obtained in normals and patients with various gastric diseases are summarized in Tables 8 and 9. 

Gastric mucosubstances belong to several classes, which are as follows. 

Proteins, Mucosubstances, and Biologically Active Components of Gastric Secretion... 

PROTEINS. MUCOSUBSTANCES. AND BIOLOGICALLY ACTIVE COMPONENTS OF GASTRIC SECRETION ... 

For many years, the facility of the hydrochloric acid assay in gastric juice and the unavailability of good quantitative techniques for fractionation of proteins and mucosubstances have directed the interest of researchers toward the study of hydrochloric acid in the stomach. The only other material in gastric juice, studied and quantitated for many years and representative of the nondialyzable gastric secretory products, was pepsin. Study of other large molecular components has been hampered by the complexity of gastric juice, technical diflSculties encountered in its fractionation, and lack of adequate quantitative methods for the assay of these materials. 

Gastric secretion represents a very complex naixture of electrolytes, water, carbohydrates, proteins, peptides, and amino acids, which are partly in solution and partly in more or less stable suspension. The large molecular materials of gastric secretion include enzymes, mucosubstances, serum proteins, peptides and products of proteolytic degradation of gastric proteins and mucoproteins, and blood group substances. 

Visible mucus forms the external layer of Hollander s so-called protective gastric mucous barrier (H28-H30). According to him, the internal layer of this barrier consists of the preformed mucosubstances contained within the juxtaluminal portion of the surface epithelial cells themselves. 

The existence of more than one mucoprotein in the dissolved mucin fraction of the gastric juice was further substantiated in our laboratory (G26, G27, G36). We found (G27) that the composition of dissolved mucin varied markedly, depending upon the stimulus applied to gastric secretion. These variations included degree of hydration, extractability with 60% alcohol, and content of tyrosine, nitrogen, and reducing substances. We therefore postulated that, in man, at least two but probably three different mucous substances were present within the mixture of mucosubstances called dissolved gastric mucin (Gll, G27) (Fig. 16). 

As we know at present, the mucoproteose fraction includes the following materials (1) most of the gastric fucomucins, as well as some of the blood group substances, i.e., most of the neutral polysaccharides of the dissolved mucin fraction linked to their peptide moiety, (2) y-globulin and probably also P-globulin, which pass into the gastric juice from the serum (G16, G42, Hll, H20, H55) and probably account for the presence of mannose in this fraction (Gll), (3) some of the pep-tidic degradation products of serum albumin and visible mucus, which are partly dialyzable (G16, K2), (4) native intrinsic factor, the related primary vitamin Bi2 binder, and tertiary vitamin Bia binder related to the neutral mucosubstances (G14, Ul, U2). 

The fact that dissolved mucin produces turbidity with acetic or trichloroacetic acid (G2, S40) has been the basis of other techniques. However, the opacity produced by various mucosubstances at the same concentration differs markedly under similar conditions, and may be caused not only by mucosubstances, but by proteins contained in gastric juice as well, lessening the value of these techniques. This applies to other methods (B35) which measure opacity development upon addition of alcohol to the total filtrate of gastric juice after sulfosalicylic acid precipitation. Here, the acid precipitation partly removes some of the products of mucus digestion, and the method is standardized on submaxillary mucin with physicochemical features different from those of gastric mucin. 

Determination of total nitrogen content of the gastric juice, introduced by Wolff and Junghans (W22) and used later by others (D4), is inadequate for quantitation of gastric juice mucosubstances because proteins, peptides, and amino acids contribute to this measurement. Other authors precipitated gastric juice with methyl alcohol or acetone and determined the amount of alkali bound by the precipitate (M4-M6). These methods determined only the buffer capacity of the precipitate,... 

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