402 4. ALLOXAN 



mation of acetaldehyde, but no stimulation was observed with other sub- 

 strates, such as lactate, pyruvate, citrate, succinate, acetate, and others. 

 The acceleration of ethanol oxidation is slight in kidney and absent in 

 brain suspensions. It is likely that this effect is due to the hydrogen-trans- 

 porting ability of alloxan, but methylene blue had no such effect on ethanol 

 oxidation. Even though alloxan could participate in hydrogen transfer 

 with the other substrates, it probably inhibits some of the cycle enzymes 

 so potently that the stimulation would not be evident. However, other 

 instances of respiratory stimulation have been reported for rat liver ho- 

 mogenates (Klebanoff, 1955), erythrocytes (Robuschi, 1952), and myco- 

 bacteria (Miiller et al., 1960). Some increased oxygen uptake could be 

 nonenzymic, the result of the oxidation of thiols or ascorbate with sub- 

 sequent oxidation of dialurate by oxygen. Respiration may also be depressed 

 by alloxan, as in rat diaphragm (Gray and DeLuca, 1955), dog kidney 

 (Villasante and Diaz, 1950), or cornea (Langham, 1953), or apparently 

 unaffected, as has been reported in a number of tissues. Mechanisms by 

 which alloxan can alter respiration are so manifold that simple experiments 

 demonstrating either stimulation or depression are not usually interpretable. 



Carbohydrate Metabolism 



The uptake of glucose by diaphragm is surprisingly resistant to alloxan, 

 since Haft and Mirsky (1952) found no effect dt 10-50 mM, and Gray 

 and DeLuca (1955) observed only a 20-25% depression at 500 mM (in 

 both cases, media kept at pH 3.5 to increase the stability of the alloxan), 

 LeFevre (1948) stated that the uptake of glucose in erythrocytes is in- 

 hibited by alloxan but gave no data. The lack of effect with muscle would 

 not be expected in view of the sensitivity of hexokinase to alloxan, but 

 it may be that under the rather abnormal conditions used the uptake 

 was governed by simple diffusion rather than phosphorylation. Both Haft 

 and Mirsky (1952) and Gray and DeLuca (1955) agree that the conversion 

 of glucose to glycogen is blocked by alloxan in diaphragm; indeed, instead 

 of glycogen synthesis, one finds a loss of glycogen (one must remember the 

 very high concentrations of alloxan used in this work). Gluconeogenesis 

 from lactate in liver is well inhibited by alloxan (Carrasco-Formiguera and 

 Mendoza, 1950); this may be an expression of actions on the EM pathway. 

 Glycogenolysis to form glucose in liver slices is not affected by 1.4 mM 

 alloxan (Canzanelli et al., 1946), but in perfused liver both the spontaneous 

 and epinephrine-induced release of glucose is blocked by the injection 

 of 10 mg alloxan into the perfusion fluid (Goldner and Jauregui, 1953). 

 These effects on the liver are believed by some to explain certain phases 

 of the blood glucose curve after administration of alloxan. Gray and DeLuca 

 (1955) have emphasized that vitamin E is antagonistic to the actions of 

 alloxan on carbohydrate metabolism in diaphragm, and it appears that 



