1 6 Endocrine Factors in Food Absorption 



tion of sugars, we studied the concentration of the various fractions of acid- 

 soluble phosphate in the intestinal mucosa during absorption of dextrose in 

 normal, in hyperthyroid, and in thyroidectomized rats, and compared it to 

 that observed during the absorption of sodium chloride.* The results indicate 

 that the absorption of glucose is accompanied by a slight increase (15 per cent) 

 in the acid-soluble phosphate esters over that observed during the absorption 

 of sodium chloride. On the other hand, the rate of absorption of dextrose as 

 influenced by the thyroid gland had no statistically significant effect on the 

 concentration of these esters. A positive correlation between the concentration 

 of various phosphates in the mucosa and the rate of absorption would have 

 supported the hypothesis that phosphorylation is concerned with selective 

 absorption of dextrose. A lack of correlation need not militate against this 

 assumption because, if the velocity of formation and the velocity of disap- 

 pearance of the esters are equal, the concentration of the hexose phosphate 

 will be governed by the conditions of the steady state. Accordingly, a differ- 

 ence in the rate of turnover of the acid-soluble phosphates need not be accom- 

 panied by a change in concentration. 



The question has been raised whether a similarity exists between the mech- 

 anism of absorption of dextrose in the intestinal mucosa and that of resorption 

 of dextrose from the glomerular filtrate in the renal tubide.*'^ In both in- 

 stances absorption involves a selective and active transfer of dextrose across 

 an epithelial barrier at a rate independent of concentration. Also, phlorizin 

 decreases the rate of absorption of dextrose in both organs. Therefore a study 

 of the rate of absorption of dextrose in the renal tubules of three female dogs 

 was made by the method of Shannon and Fisher" before and after the dogs 

 were rendered hyperthyroid. The renal tubules of the first dog resorbed 170 

 mg. of dextrose (average of four experiments) in the normal state and 250 mg. 

 (average of three experiments) after administration of thyroxin. In the second 

 dog, thyroxin increased tvibular resorption from 200 mg. (average of three ex- 

 periments) to 280 mg. (average of two experiments).^ In the third dog the fig- 

 ures were 214 mg. (average of four experiments) and 335 mg. (average of two 

 experiments), respectively. The possibility that this increase was due to an ele- 

 vation of body temperature was ruled out as far as possible by measurements 

 of the rectal temperature. 



This experiment supports the conception of an essential similarity between 

 the absorptive mechanism of dextrose in the intestinal mucosa and in the 

 renal tubule. It also strengthens the hypothesis that preferential intestinal 

 absorption of dextrose takes place through phosphorylation because Kalckar* 

 and Colowick, Welch and Cori" demonstrated that extracts of the kidney 

 possess the ability to phosphorylate dextrose. Finally, the data obtained from 

 these experiments offer strong evidence in favor of the specificity of the stimu- 

 lating action of the thyroid hormone on selective absorption of dextrose in 

 the intestine and in the kidneys; they rule out the indirect influence of any 

 physiological mechanism ivhich these tiuo organs do not share. 



