Astringents

Astringents, Adstringentia. Astringent action is considered a physicochemical process that occurs when so-called astringent substances come into contact with tissue fluids, intercellular substance, and cells of the organism, whereby an insoluble protein compound is formed on their surface and this compound precipitates, thus forming a protective film. A more intense manifestation of the same action leads to destructive changes in the entire cell or even tissues, which can cause increased local blood circulation, accelerated cell division, and increased tissue fluid (irritant action), or finally, the death of superficial and sometimes deeper layers of cells and complete destruction of the latter (cauterizing action). All three types of action are not strictly demarcated processes, differing from each other only quantitatively. To a greater or lesser degree, astringent action is possessed by numerous medicinal substances, which can be arranged into two large groups: 1) organic astringent substances-tannins ('Tannica') and 2) metallic astringent substances-salts of aluminum and many heavy metals. 1. Organic astringents. The most important representative of substances in this group is tannic acid, or tannin, C₁₃H₁₀O₇COOH; from others, one can mention: oak-tannic acid, catechu-tannic acid, kino-tannic acid, coffee-tannic acid, and many others, which received their name from the plants in which they are contained. The chemical structure of most of them is unknown; common to all is the presence of gallic acid [C₇H₂(OH)₃COOH] among their breakdown products. All of them possess a characteristic astringent and puckery taste. When they come into contact with mucous membranes, coverings, or wound surfaces, the latter become wrinkled (due to protein coagulation the cells become more compact, of smaller size), become pale (decrease in the lumen of small vessels due to contraction of their musculature or compression by surrounding tissues), and become dry (cessation of secretion of glandular cells and exudation of fluid from vessels). This is particularly manifested on inflamed tissues, | whereby exudation is reduced, the exit of leukocytes is limited or even stopped, and suppuration is diminished. When astringent substances come into contact with blood, its proteins precipitate, and the blood coagulates. These properties form the basis for the local application of A. s. as anti-inflammatory and hemostatic agents. In addition, with local application, they also exhibit weak antiseptic action, the cause of which is seen in the fact that, due to physicochemical changes in the cell surface, unfavorable conditions are created for the life activity of bacteria. Astringents are also used as deodorizing substances, since, by preventing putrefaction and changing putrefied masses, they thus destroy the foul odor. When absorbed in the intestine, A. s. combine with alkalis or proteins and enter the blood already in an altered form; this explains the absence of their astringent action on internal organs, as well as their general action on the entire organism. Astringent substances are excreted only in small quantities in unchanged form by the intestine and in traces by urine; the fate of astringents in the organism is not fully elucidated.-They are used for local action in cases of excessive secretion (in ulcers, stomatitis, gingivitis, diarrhea, etc.), in poisoning by metals and alkaloids, and as hemostatic agents. 2. Metallic astringents. These include salts of aluminum and heavy metals (silver, zinc, copper, lead, iron, mercury, bismuth, etc.). When in contact with living tissue (e.g., with the gastric mucosa), they form physicochemical compounds with proteins, namely albuminates. The degree of action (astringent; irritant or caustic) depends on the nature of the albuminate and the properties of the acid liberated during its formation. From the properties of the albuminate, its density or looseness, whether it is soluble in tissue juices, in excess of protein or NaCl, etc., play a role, since the greater the solubility, the deeper the action spreads. According to increasing solubility, Schmiedeberg arranges albuminates as follows: lead, iron, aluminum, zinc, copper, silver, and mercury, with all of them being closer to the typical insoluble lead albuminate than to the soluble mercury albuminate. Another factor determining the strength of action of metallic astringents is the degree of dissociation into ions of the acid liberated during their formation (the greater the dissociation, the stronger the action); therefore, inorganic salts act more strongly than organic ones. An example of typical purely astringent action is Plumbum aceticum; conversely, the most characteristic cauterizing action is possessed by Hydrargyrum sublimatum seu bichloratum (corrosive sublimate). From other factors affecting the strength of action of metallic astringents, one should mention: the concentration of the metal salt (the stronger, the greater the effect), the degree of affinity of the salt for water (hygroscopic salt acts more strongly), and the duration of time of action (often astringent action with repeated application turns into irritant action). The strength of antiseptic action of substances in this group depends on the concentration of the given salt, the properties of the metal itself (with no direct connection with chemical properties), the degree of dissociation of the acid into ions, etc. (see Antiseptic agents). The usual astringent action in the intestine (decreased peristalsis, constipation) with large doses of these substances passes into irritant or caustic action (gastroenteritis, necroses). Only mercury and lead are absorbed to a significant extent by the intact epithelium of the gastrointestinal tract, but with damage to its integrity, the other metals are also absorbed. After absorption into the blood, all substances in this group, in contrast to organic astringents, also exhibit their general action on the organism.

VYAZKS

(often astringent action with repeated application turns into irritant action). The strength of antiseptic action of substances in this group depends on the concentration of the given salt, the properties of the metal itself (with no direct connection with chemical properties), the degree of dissociation of the acid into ions, etc. (see Antiseptic agents). The usual astringent action in the intestine (decreased peristalsis, constipation) with large doses of these substances passes into irritant or caustic action (gastroenteritis, necroses). Only mercury and lead are absorbed to a significant extent by the intact epithelium of the gastrointestinal tract, but with damage to its integrity, the other metals are also absorbed. After absorption into the blood, all substances in this group, in contrast to organic astringents, also exhibit their general action on the organism.