232 1. lODOACETATE AND lODOACETAMIDE 



higher concentrations antagonizing the actions of acetylchoHne and K+ 

 (Haliisz et al., 1960). It was thought that iodoacetate does not interfere 

 with the synthesis or release of acetylcholine but mainly blocks the response 

 of the postganglionic cells. 



The hyperpnea induced by iodoacetate in the whole animal led several 

 investigators to study the effect of iodoacetate on the carotid area and as- 

 sociated reflexes. Winder (1937) found that perfusion of the carotid seg- 

 ment in dogs with 0.014-0.7 mM iodoacetate practically abolishes the anoxic 

 response, but that the pressoreceptor reflexes are unaffected. The anoxic 

 reflex may be related to the formation of acid within the receptor cells and 

 possibly iodoacetate inhibits this (Anichkov, 1953). A very interesting study 

 of this problem was made by Landgren et al. (1954), who recorded action 

 potentials from the sinus nerve in cats upon intracarotid injection of vary- 

 ing amounts of iodoacetate. Injection of 2 mg iodoacetate leads to an in- 

 crease in the number of potentials from chemoreceptor cells but, if the dose 

 is raised to 10 mg, these potentials are quickly abolished while the pressor 

 spikes remain unaltered; lobeline, a potent stimulator of the chemoreceptor 

 cells, is now without effect. They believed that carotid body function de- 

 pends on an acetylcholine cycle and that iodoacetate inhibits the formation 

 of acetylcholine. The respiratory effects of iodoacetate in the animal prob- 

 ably involve the carotid body, but the exact mechanism of the effect on 

 carotid function is not understood. 



EFFECTS ON THE RETINA AND THE EYE 



Retinal tissvie is of particular interest with respect to its response to 

 iodoacetate because of its very high rate of glycolysis (Table 1-36). Gly- 

 colytic activity is much higher in retina than in any other type of tissue, 

 even tumors, embryo, and bone marrow, all noted for their relatively high 

 glycolytic rates. Although the absolute Pasteur effect is also high, the per 

 cent Pasteur effect is low (0.49), being similar to tumors (0.52), whereas 

 in normal tissues and embryo it is around 0.83. The high glycolytic activity 

 does not necessarily imply that retinal function will be especially sensitive 

 to iodoacetate, inasmuch as it is the degree of dependence of the function 

 on glycolysis which is important, but it is reasonable to anticipate that, in a 

 tissue with rather unique metabolic patterns and functions, these will be 

 in some manner related. 



Retina 



Selective impairment of retinal function and damage to the retina have 

 indeed been demonstrated by Noell (1951), but before these problems are 

 discussed it will be well to review in greater detail the metabolism of the 



