350 INOSITOLS 



mals after absorption of the test dose was complete) was in a form not 

 available to the strain of yeast used in these assays. 



The urinary excretion of inositol varied from 3 to 5 mg. per rat for a 

 24-hour period and was not significantly greater for the rats which had 

 received from 260 to 335 mg. of inositol per os than for the fasted control 

 rats. The limit of accuracy of the inositol assay permits the conclusion 

 that urinary excretion accounted for less than 1 % of the administered 

 inositol. 



The absorption of inositol monophosphate was also studied.''^ From 150 

 to 200 mg. of the monophosphate isolated from soybean lipositol was 

 administered to 200-g. rats. The rate of absorption appeared to be more 

 rapid than for inositol, especially during the first 2 hours. Approximately 

 80 % of the dose was absorbed in from 1 to 2 hours, and complete absorption 

 occurred in rats killed at 12 and 24 hours. In all animals killed later than 

 2 hours after administering inositol monophosphate, almost all the inositol 

 in the intestinal contents was found to be in a form available to the assay 

 organism. Since the original isolated inositol monophosphate gave a growth 

 response equivalent to only 8 to 15 % of its contained inositol, it appeared 

 that the phosphoric ester was rapidly hydrolyzed in the intestine. The 

 initial rapid disappearance of inositol might indicate an extremely rapid 

 absorption of the inositol monophosphate per se, with subsequent slow 

 absorption of the free inositol which was presumably liberated by intestinal 

 phosphatases. 



Other bound forms of mi/o-inositol are also apparently readily hydrolyzed 

 in the intestinal tract of animals. For example, phytin can supply both the 

 inositoF^ and inorganic phosphate requirements of rodents. Soybean ce- 

 phalin and even synthetic inositol hexaacetate can replace dietary inositol 

 for the mouse, indicating that they are cleaved to free inositol.^^ 



Intraperitoneally administered m^/o-inositol appears to be absorbed, 

 since it is as effective in depressing ketone body excretion in fasted rats 

 as is the orally administered compound.''^ 



6. Cataholism 



Inositols are isomeric with the common 6-carbon sugars, and perhaps 

 for this reason the possible conversion of myo-inositol to carbohydrate or 

 carbohydrate breakdown products in animal tissues has been studied by 

 many investigators. Although earlier results were inconclusive, it is now 

 certain that inositol is metabolized, at least in part, like carbohydrate. 

 Stetten and Stetten'^^ fed deuterium-labeled myo-inositol to a phlorhizin- 

 ized rat and found that at least 7 % of the dose fed appeared in urinary 



'* D. W. Woolley, /. Biol. Chem. 140, 461 (1941). 



^6 M. R. Stetten and D. W. Stetten, Jr., J. Biol. Chem. 164, 85 (1946). 



