190 1. lODO ACETATE AND lODOACETAMIDE 



lumen but has no effect on the movement of xylose. Injected subcutaneously 

 (0.12-0.16 mg/g) it tends to bring the absorption rates of all sugars to a 

 common level, which is that of passive diffusion (in the accompanying tab- 

 ulation, around 21%). In other words, iodoacetate blocks active transport 



without altering passive diffusion. Iodoacetate was found to depress phos- 

 phorylation of glucose in intestinal extracts, and it was postulate that this 

 is the mechanism of the inhibition in the intact tissue. These results and 

 conclusions have been questioned by later workers. Westenbrink (1936) 

 found that iodoacetate inhibits the absorption of both glucose and xylose 

 from the intact rat intestine, and felt that the site of action is not the me- 

 tabolism of the intestinal mucosa but the intestinal circulation. Klinghoffer 

 (1938) also found that iodoacetate given subcutaneously (0.06-0.2 mg/g) 

 reduces the absorption of glucose, xylose, and NaCl to approximately equal 

 degrees, and concluded that the action is nonspecific since pylorospasm, 

 hemorrhagic enteritis, and other evidence of intestinal damage were ob- 

 served. Ohnell and Hober (1939) reported that 0.1-0.16 mg/g iodoacetate 

 given subcutaneously to rats leads to spastic contractions of the intestine, 

 accelerated mucus secretion, and damage to the epithelial villi. However, 

 glucose absorption is inhibited a good deal more than that of xylose. These 

 discrepancies have never been resolved. 



Further studies on the characteristics of the iodoacetate inhibition of 

 glucose transport have not simplified the picture. Laszt (1939) found that 

 injections of NaCl previous to iodoacetate completely prevent the inhibition 

 of intestinal glucose absorption. Since the relation between iodoacetate ac- 

 tion and NaCl has not been examined in isolated intestine, it is impossible 

 to decide whether this is a local or a systemic phenomenon. Another strange 

 observation, that iodoacetate counteracts the depressant action of 2,4-dini- 

 trophenol on glucose absorption, was made by Rummel et al. (1958). An 

 inhibition of 88% is given by 0.1 mM 2,4-dinitrophenol alone and 50% by 

 1 mM iodoacetate alone; however, in the presence of both inhibitors the 

 inhibition is 61% — thus iodoacetate stimulates transport when it is inhib- 



