CHAPTER XL THE AROMATIC SUBSTANCES IN URINE THE aromatic substances which occur in urine belong to four classes : (1) Hippuric acid, and similar aromatic compounds of glycocine. (2) Combinations of glycuronic acid with aromatic substances. (3) Aromatic oxy-acids. (4) Ethereal sulphates. HIPPURIC ACID This substance is chiefly of interest, as it is one of the best instances of synthesis occurring in animals. The method of preparing it from urine has already been given (p. 719), and its relation to aromatic bodies has been also briefly described (p. 77). It appears in human urine in abundance after ingestion of benzoic acid, of other aromatic substances related to benzoic acid, or of vegetable tissues containing such substances. Its large amount in the urine of herbivora is thus due to the benzoic acid in their food; the benzoic acid taken into the body unites with glycocine to form hippuric acid and water. C2H6O2+C2H ̧NO2=C„H„NO3 + H¿O. [benzoic acid] [glycocine] [hippuric acid] Hippuric acid occurs in the urine to a small extent, however, even in starving animals, and is thus a product of the metabolism of the animal tissues. A third source of hippuric acid is as a result of putrefactive processes in the alimentary canal. The products of putrefaction are partly absorbed, and pass thence to the urine; an intermediate stage in the formation of hippuric acid in this way is phenyipropionic acid (Salkowski,' Tappeiner 2). Properties of hippuric acid. It is a monobasic acid, which crystallises in transparent, colourless, four-sided prisms (fig. 96). It has a bitter taste, but no smell. It is readily soluble in hot alcohol or ether, but only slightly soluble in water. Under the action of Ber. deutsch. chem. Ges. xi. 500. 2 Zeit. Biol. xxii. 236. mineral acids it takes up water and splits into its components, glycocine and benzoic acid. Like sugar, it reduces alkaline solutions of cupric hydrate, such as Fehling's solution. Quantity in urine.-In human urine from 0.3 to 3.8 grammes (5 to 50 grains) are excreted per diem. In the urine of herbivora it replaces uric acid to a great extent. The urine of sucking calves who receive no vegetable food is almost free from hippuric acid. The acid is not free in the urine, but occurs as hippurates of the alkalis. With the exception of traces of hippuric acid, due to metabolism and intestinal putrefaction, the appearance of this substance is a mere matter of diet. The chief experiments that bear out this point are as follows: : FIG. 96. Hippuric Acid Crystals. The urine of rabbits fed on pure grass contains little hippuric acid; that of those fed on dandelions contains much.' The urine of sheep fed on potatoes contains little; of those fed on potatoes plus benzoic acid much hippuric acid.2 Plums, pears, cranberries increase its amount in the urine. The cuticular parts of many plants act similarly. The administration of many drugs which are related to benzoic acid acts similarly; among these toluol,' oil of bitter almonds, benzylamine, cinnamic acid, phenylpropionic acid may be mentioned. 7 The amount of hippuric acid is also said to be increased in the urine in certain diseases of the liver, including diabetes and jaundice. This cause, however, is in a different category to the preceding. 8 Where is hippuric acid formed?-Although one observer, Salomon, found hippuric acid in the muscles and liver of rabbits from which the kidney had been removed, the greater number of experimentalists have located the seat of the union of benzoic acid with glycocine to form hippuric acid in the kidneys themselves (Meissner and Shepard,9 Schmiedeberg and Bunge 10), and have failed to find that the synthesis occurs after removal of the kidneys. Schmiedeberg and Bunge also found that the synthesis was effected by the living (i.e. recently excised) kidneys. 1 Wildt, Maly's Jahresb. 1873, p. 133. 3 Lücke, Arch. pathol. Anat. xix. 196. 5 Schmiedeberg, Arch. exper. Path. viii. 11. 2 Schröder, Zeit. physiol. Chem. iii. 323. + Munk, Pflüger's Archiv, xii. 142. 7 Salkowski, Journ. prakt. Chem. N.F. xii. 653. 8 Zeit. physiol. Chem. iii. 365. 9 Untersuch. ü. d. Entstehen der Hippursäure, Hanover, 1866. 10 Arch. f. exp. Path. u. Pharm. vi. 233. See also Kochs, Pflüger's Arch. xx. 64. Substances which resemble Hippuric Acid In birds benzoic acid unites, not with glycocine, but with a base (which has the formula C,H12N2O2, to form a substance called ornithuric acid (C,HN0,) (Jaffe,' Meyer'), Hoppe-Seyler gives a list of twelve glycocine unions that are formed by the administration of different aromatic substances. Out of these that which occurs in the urine after the administration of salicylic acid may be mentioned, as salicylic acid is a most important drug; the substance in the urine is called salicyluric acid,' its formula being C,H(OH)NO,. This may be detected in the urine by the bluish violet colour it gives with a few drops of dilute solution of ferric chloride. Combinations of Glycuronic Acid This substance, which is closely related to the carbohydrates, and is apt to be mistaken for sugar in urine, does not occur in normal urine, or only in mere traces. It will, therefore, be more appropriately dealt with in the chapter on the abnormal constituents of the urine. It occurs only partially in combination with aromatic substances." Aromatic Oxy-acids Two of these, hydroparacumaric acid or oxyphenylpropionic acid and paraoxyphenylacetic acid, are found in minute quantities in the urine (see also p. 78).“ ETHEREAL SULPHATES Städeler in 1851 discovered that on distilling the urine of oxen and men with dilute sulphuric acid he obtained in the distillate small quantities of phenol or carbolic acid. Buliginski, and later HoppeSeyler, showed that phenol is not present free in the urine, but as a compound, from which it is liberated by the sulphuric acid employed in distillation. It was, however, not until 1876 that Baumann 10 discovered that this compound is an ethereal combination of phenol with sulphuric acid. He also found the presence of other similar ethereal sulphates in the urine; these are compounds of the radicle HSO, and are sometimes incorrectly termed sulphonates. The most important of these substances are the ethereal potassium sulphates of phenol, cresol, catechol or pyrocatechin, indole, and skatole. In a more recent paper Baumann 11 announces that after the separation of these from the urine others still remain; but these have not yet been separated or identified. 1 Ber. deutsch, chem. Ges. x. 1925; xi. 406. 2 Ibid. x. 1930. 3 Physiol. Chem. p. 835. Full references are here given. 4 Bertagrimi, Ann. Chem. Pharm. xcvii. 248. 5 E. Kütz has recently (Zeit. Biol. xxvii. 247) described the properties of the compounds which glycuronic acid forms with various aromatic substances, administered as drugs. 6 For the separation of these substances see Salkowski, Lehre vom Harn. 7 Ann. Chem. Pharm. lxxvii. 17. 9 Pflüger's Archiv, v. 470. 11 Zeit. physiol. Chem. x. 123. Hoppe-Seyler's Med. chem. Unters. p. 234. 10 Ibid. xii. 69; xiii. 285. In herbivora these compounds are more abundant in the urine than in flesh feeders like dogs, or those who live on a mixed diet like man. They are, however, found in small quantities in the urine of all animals. They appear to have one or both of two origins: first, from the aromatic substances in the food; hence their greater abundance in the urine of herbivora; secondly, they arise in the intestine as a result of putrefaction. They are absorbed from the intestine, pass into the blood-stream, and are eliminated in combination with potassium as ethereal sulphates in the urine. The synthesis probably occurs in the liver (Baumann). In animals like dogs and men, whose food contains little or nothing of an aromatic nature, the origin of the ethereal sulphates appears to be wholly under the second of these headings. If putrefaction be entirely stopped in the alimentary canal, these bodies completely disappear from the urine. Putrefaction can be put a stop to in the intestine of dogs by inanition plus the administration of large doses of calomel (Baumann, Morax1) or iodoform (Morax). In men, however, it is not possible to give doses of these drugs sufficiently large for the purpose. Baumann, however, was fortunate enough to make observations on a patient who had a fistula in the upper part of the intestine, and whose intestine below this was functionless; putrefactive processes did not occur, and these salts were absent from the urine. A large number of analyses have been made as to the relation of the ethereal sulphates to the total sulphates of the urine in man, and in round numbers the normal proportion may be stated as 1:10. The method employed in this analysis will be described in the chapter on Quantitative Analysis of Urine. In morbid urines the same subject has been investigated by numerous analysts, among whom may be particularly mentioned G. Hoppe-Seyler in Germany, and J. S. Haldane in this country. It is found that in those diseases in which putrefaction in the intestines, or elsewhere in the body, is increased, the proportion of ethereal sulphates rises. G. Hoppe-Seyler's results may be summarised as follows: (1) Deficient absorption of the normal products of digestion, such as occurs in peritonitis and tubercular disease of the intestine, leads to an increase of the ethereal sulphates in the urine, because the products of digestion undergo putrefactive changes, and the putrefactive products are absorbed. (2) Diseases of the stomach, in which the food lies in the stomach a long time and undergoes fermentative changes, always lead to an increase of the ethereal sulphates in the urine. (3) Simple constipation and typhoid fever do not produce this result. 1 Zeit. physiol. Chem. x. 318. 2 Ibid. xii. 1. 3 Journ. of Physiol. ix. 213. (4) Putrefactive processes outside the alimentary canal, putrid cystitis, putrid abscesses, putrid peritonitis, &c. have the same result as putrefactive processes within the intestine. The amount of the ethereal sulphates is, moreover, in all cases proportional to the severity of the putrefaction, and is increased by the retention and diminished by the discharge of putrid matter; as, for instance, on opening the abscess. It has by these and other observations been conclusively shown that the best criterion of the occurrence and amount of putrefaction in the body is the relation of the ethereal sulphates to the total sulphates. Brieger's method of estimating putrefactive change was by estimating the total quantity of phenol in the distillate from acid urine as tribromophenol. He found that it was increased in septic conditions.' This method is, however, open to two objections: first, it only takes into account one of the many products of putrefaction; and, secondly, as an analytical method, it is open to criticism. This latter point has been especially insisted on by Haldane, who found that the more concentrated the urine is, the greater is the quantity of tribromophenol to be obtained from it. The non-recognition of this source of error has led Brieger to classify scarlet fever and diphtheria with pyæmia, erysipelas, and other putrefaction processes, whereas the increase of phenol noted in these cases is merely due to the greater concentration of the urine that occurs. Haldane found, by the more accurate method of estimating the relation of ethereal sulphates to total sulphates, that the proportion is not increased, but if anything somewhat diminished; hence there are no grounds for classifying scarlet fever and diphtheria as putrefaction diseases except when complicated by the formation of putrid abscesses. We must now pass from general considerations to consider the individual members of the group. Phenol-sulphate of potassium.-The formula for carbolic acid or phenol is CHO. This was first found to be one of the products of intestinal putrefaction by Baumann.2 This is absorbed and excreted as the phenol-sulphate of potassium (CH,O.SO,K) in the urine. Some of this sulphate also comes from tyrosine, which passes through the stages of paracresol and paraoxybenzoic acid before it is converted into the phenol salt (Baumann 2). Phenol may be obtained from urine by distilling it with sulphurie or hydrochloric acid. This breaks up the phenol sulphate, and phenol passes into the distillate, where it may be recognised by the yellow precipitate of tribromophenol which it gives with bromine water, or by the various colour-reactions already enumerated (p. 77). 1 Centralbl. med. Wiss. 1878, No. 30; Zeit. physiol. Chem. ii. 241. 2 Zeit. physiol. Chem. i. 60; iii. 250. The view here advanced by Baumann as to the fate of tyrosine is not universally accepted; thus Blendermann (Abst. Journal Chem. Soc. 1883, p. 876) and Jaffe (Zeit, physiol. Chem. vii.) by feeding animals with tyrosine found no increase of aromatic or any other substances in the urine. Intravenous injection of tyrosine was followed by a similar negative result (Cohn, Ibid. xiv. 189). |