Indican

INDICAN, 1) a glycoside of the plant Isatis tinctoria, which upon hydrolysis yields glucose and indoxyl; it has technical importance for obtaining the dye indigo; 2) in medical disciplines, indican is commonly (incorrectly) used to refer to the potassium salt of the ethyl-sulfuric acid of indoxyl (see Indole)- the so-called "urinary indican" and "blood indican". Indoxyl is formed from the amino acid tryptophan (a product of tryptic digestion of proteins), which in the human intestine gives rise to indol through the action of putrefactive processes (Bact. coli, Proteus, Bac. perfringens Welchii). Under normal conditions, indol formation occurs in the large intestine due to small amounts of amino acids escaping absorption in the upper part of the intestine; under pathological conditions, indol formation increases, especially with stasis of intestinal contents. The determination of indol in feces can only to a certain degree serve as a measure of its formation in the intestine. Indol is absorbed in the intestine, oxidized to indoxyl (/S-oxyindol-C₈H₆N.OH), and retained by the liver, which partly destroys it and partly forms a conjugate with sulfuric acid and - to a lesser extent- with glucuronic acid. Only in the form of these conjugates does indoxyl circulate in the peripheral blood (I. k r o v i) and is excreted by the kidneys (urinary I.). The origin of indoxyl from indol has been proven by feeding experiments with the latter in animals. However, a considerable part of indol introduced orally or parenterally is lost in these experiments (destroyed in the body or excreted in unknown compounds).- j Chemical reactions for I. are based on the cleavage of the conjugate by strong acids and oxidation of indoxyl to blue indigo or to the formation of red indigo. Indicanemia. Under normal conditions, small amounts of I. are present in the blood serum, not detectable by ordinary qualitative reactions. The introduction into clinical practice of more sensitive colorimetric methods of determination has revealed cases of pathological hyper-indicanemia, i.e., content of I. in blood exceeding 0.13 mg%. The greatest significance is renal hyperindicanemia: in true uremia, the content of I. in blood is significantly increased, as was first found (even by a qualitative test) by Obermeyer and as this was confirmed by subsequent authors (increase up to 7.20 mg% according to Waag). According to Haas, any hyperindicanemia above 0.16 mg% indicates renal insufficiency. This rule is justified with rare exceptions. In chronic azotemia, hyperindicanemia often occurs earlier, is prognostically more serious, and is relatively more pronounced than the increase in RN (residual nitrogen) of the blood. In acute uremia, hyperindicanemia develops later compared to the increase in RN. In stagnant kidney, hyperindicanemia does not occur despite the increase in RN; however, in cyanotic induration of the kidneys, hyperindicanemia is observed as a manifestation of renal insufficiency. In essential hypertension, despite the absence of other symptoms of renal insufficiency, Baar found slight hyperindicanemia. Conversely, in nephroses, I. is not increased in the blood or is not determined at all. Urologists attribute importance to hyperindicanemia in establishing chronic renal insufficiency in patients with prostate conditions. In toxicoses of pregnancy, even greater increases in physiological hyperindicanemia of pregnancy may be observed. In renal retention, as in normal conditions, I. accumulates mainly in the serum, not in the red blood cells (Baar); also in the body tissues, I. penetrates in small amounts; thus, Becher found in tissues in uremia indican 6-12 times less than in the serum. Therefore, the presence of hyperindicanemia more correctly reflects the contamination of the body with unexcreted waste products than the increase in blood RN, which to a considerable extent can accumulate in tissues. In severe uremia, I. passes into the cerebrospinal fluid, but not constantly; also in exudates, I. is less than in the serum (Dubnova). The pathogenetic significance of hyperindicanemia for the uremic syndrome is controversial. I. is considered rather an indicator than a poison of uremia. I. does not act toxicologically, at least in acute experiments; thus, the intravenous injection of 0.04 g of I. in a dog is tolerated without the slightest signs of poisoning. The prolonged action of indol and other aromatic substances leads to the development of atheromatosis and visceral scleroses. According to Becher, however, uremic coma is also a poisoning by unneutralized aromatic products of protein breakdown, a kind of intestinal auto-intoxication. It should be noted that some authors are skeptical about the prognostic significance of hyperindicanemia (Auisenda, Rienter). An increase in I. in the blood is also observed without kidney damage in diseases of the liver, in severe anemias, and in diseases of the gastrointestinal tract (for example, in Baar's material in a patient with stomach ulcer- 0.8 mg%). In these cases, part of the hyperindicanemia is considered of extra-intestinal origin; for example, in liver diseases, hyperindicanemia occurs regardless of the intensity of intestinal putrefaction (Rosenberg, Haas); in malignant anemia, Baar found in venous blood I. more than in arterial blood (metabolic tissue indicanemia). The presence of hyperindicanemia besides kidney diseases has no diagnostic significance at present.- Quantitative determination of I. in blood in the clinic is based on the formation in the presence of thymol of cymol-indolignon (Jolles' reaction). Technique according to Rosenberg: in 10 cm³ of serum, proteins are precipitated by adding an equal amount of 20% trichloroacetic acid; to 10 cm³ of filtrate, 1 cm³ of 5% alcoholic solution of thymol and 10 cm³ of Obermeyer's reagent (2 g of ferrous chloride per 1 liter of strong HCl-specific weight 1.19) are added; the pigment formed is extracted after 20 minutes with 2 cm₃ of chloroform. Further, colorimetry is performed with a standard solution of indolignon or the content of I. is determined minimetrically by setting up a series of tests with different dilutions of serum (sensitivity limit of the reaction-0.003 mg I. in 10 cm³ of the test liquid). In the modification by Haas (precipitation of proteins by alcohol), the values of I. are 1.6 times smaller than in the technique by Rosenberg. Indicanuria. I. is already present in urine under normal conditions in an average amount of 0.65 mg% (according to Mai Hard, in normal conditions up to 12-32 mg per day); indoxyl is excreted in urine only in bound state, mainly with sulfuric acid, to a lesser extent- with glucuronic acid; the latter combination is unstable and easily destroyed by putrefactive bacteria, therefore with excess excretion of glucuronic compound, urine in rare cases may spontaneously take a blue tint due to the formation of blue indigo or more rarely- red due to indirubin. Pathological hyperindicanuria is observed with various gastrointestinal disorders, with achylia, with increased putrefaction in the intestine, with intestinal obstruction, especially with stasis in the small intestines. Constipation as such does not cause hyperindicanuria (Baar); also indicanuria is not parallel to the general symptoms of intestinal auto-intoxication and therefore cannot be a measure of it (van der Reis). Urine of sterilely cultivated experimental animals does not contain even traces of I., which confirms its microbial origin (Mechnikov, Vollmann). Labbe and Vitry, however, found with excess protein diet hyperindicanuria even with normal digestive processes. Hyperindicanuria is also observed in liver diseases as a manifestation of its functional insufficiency (cirrhosis, cancer, fatty degeneration of the liver). It has been proven by experiments on hepatectomized frogs that indol injected subcutaneously in an amount of 1 mg to such animals is not metabolized by the liver and (in contrast to normal frogs) is hardly excreted in urine in the form of indican. Gilbert and Weil proposed to study in the clinic the indol-excretory function of the liver by testing for provoked indicanuria (after oral administration of 1 mg of indol)- under these conditions, in contrast to experiments on frogs, indicanuria is enhanced only in liver diseases. According to Achard, indicanuria in liver insufficiency can be provoked by introducing sugar into the digestive tract (per os or per rectum). In general, indicanuria is a controversial symptom of liver insufficiency, having relative practical significance. Apparently indicanuria is sometimes observed also with extra-intestinal disturbance of protein metabolism of the body with formation of indol from body tissues under the action of unorganized enzymes, e.g. in cancer, starvation, anemias, especially-pernicious (up to 2.6 mg%). In another form of extra-intestinal indicanuria- septic indicanuria (Mae Kee)- despite the small amount of indol in the intestine, indicanuria occurs due to bacterial decomposition of body proteins and pathological secretions in putrefactive bronchitis, gangrenous foci, tuberculous cavities.-P reduced excretion of I. with urine is observed first of all in chronic kidney lesions accompanied by uremia; further- in experimental ligation of ductus pancreatici and in the clinic in diseases of the pancreas (up to anindicanuria) (Gerhardt, Glassner, v. Noorden).

Indicanuria is noted in the disease of Basedow: according to Harries, with this disease the intestinal flora lacks indole formers, and tryptophan is completely absorbed as such. In general, the conditions for the excretion of I. by urine must still be considered insufficiently studied. The reactions of I. in urine are based on the formation of blue indigo under the action of Obermeyer's reagent and its extraction with chloroform—a qualitative test (with such treatment, iodides give a pinkish coloration to the chloroform, which disappears upon shaking with a crystal of hyposulfite); quantitative determination is based either on converting I. first into indigo and then sulfonating it into indigosulfonic acid with subsequent titration with potassium permanganate (MaiHard), or on the formation of indigo-red and its colorimetric determination, or on the minimetric method according to the principle of the Jolles reaction.