Phloridzin

PHLORIDZIN, a glycoside from the bark of apple roots, consisting of glucose and phloretin (an ester of p-oxyphenylpropionic acid and phloroglucinol). It is a crystalline substance with a bitter taste, insoluble in cold water, and easily soluble in alkalies and hot water. Its solution oxidizes in the air, turning brown. Phloridzin is interesting because after its injection into animals (0.5–1 g per 1 kg of body weight), temporary glycosuria sets in, the so-called phloridzin diabetes. Blood sugar in phloridzin glycosuria is not elevated, and is often even lowered. With repeated injections of phloridzin in starving animals, sugar excretion continues until the glycogen reserves in the body are completely exhausted and proceeds further at the expense of protein breakdown and the conversion of amino acids into sugar. Phloridzin diabetes played an important role in physiology as a method for studying intermediary carbohydrate metabolism and, in particular, the process of the new formation of sugars from non-carbohydrate food substances (amino acids, etc.). It has been proven that the action of phloridzin is directed mainly at the epithelium of the renal tubules and that phloridzin diabetes represents a renal form of glycosuria. Formerly, the action of phloridzin was interpreted as an "increase in the permeability of the renal filter for glucose." According to modern physiological concepts, no such filter exists (see Diuresis). Normally, a filtrate containing glucose in the same concentration as blood plasma is excreted in the renal glomeruli; in the tubules, glucose undergoes reabsorption. Phloridzin inhibits this glucose resorption in the tubules. Recent works by Verzar, Lundsgaard, and Wertheimer (Verzar, Lundsgaard, Wertheimer) have shown that the absorption of sugars both in the intestine and in the renal tubules is associated with the phosphorylation of sugars and is inhibited by specific poisons of phosphorylation (iodoacetic acid). Lundsgaard showed that phloridzin, when administered per os, also inhibits the absorption of sugars in the intestine; at the same time, it has the ability to stop muscle glycolysis and yeast fermentation by preventing phosphorylation. The localization of the action of injected phloridzin in the kidneys is explained solely by the fact that only in the kidney does phloridzin accumulate in a sufficiently high concentration. Phloridzin acts similarly, though more weakly, through its aglycone phloretin and (according to Abderhalden) a number of other glycosides of the aromatic series. Lit.: Abderhalden B. und Flckemann G., Über den Einfluss von a- und B-Glucosiden auf die Phosphorylierung von Traubenzucker, Biochem. Zeitschr., B. CCLXVIII, 1934; Lundsgaard E., Die Wirkung von Phlorrhizin auf die Glucoseresorption, ibid., B. CCLXIV, 1933; Wertheimer E., Phloridzinwirkung auf die Zuckerresorption, Pflüger's Arch. f. d. ges. Physiol., B. CCXXXIII, 1933.

A. Braunshtein.