380 4. ALLOXAN 



urate formed from alloxan may be similarly detected. The fiuorometric 

 methods devised by Karrer et al. (1945) and Tipson and Cretcher (1950) 

 are to be preferred, especially the latter. In the former case, alloxan was 

 reacted with iV-methyl-o-phenylenediamine to form a fluorescent deriva- 

 tive, thought to be 9-methylisoalloxazine but probably not, and, in the 

 latter case, riboflavin is formed by condensation of alloxan with d-1- 

 ribitylamino-2-amino-4,5-dimethylbenzene, this method being able to meas- 

 ure alloxan concentrations down to 0.01 //g/ml or 0.00007 raM. It might 

 be suggested that in determinations of alloxan in biological material, 

 especially in attempts to detect endogenous alloxan, several methods be 

 used to increase the specificity. 



DIABETOGENIC ACTION 



We shall depart from the usual sequence of presentation in these volumes 

 in the discussion of alloxan inasmuch as the production of pancreatic islet 

 damage and diabetes is the most interesting aspect of this inhibitor, and 

 for this reason it may be best to summarize briefly what is known of this 

 before discussing the effects of alloxan on enzymes and metabolic pathways. 

 Alloxan in the proper dosage can specifically damage the pancreatic islet 

 /5-cells, resulting in their disappearance within a few days, accompanied by 

 a typical and permanent diabetes mellitus due to the failure in insulin se- 

 cretion. If the dosage of alloxan is higher than required to damage the 

 /?-cells, definite eff'ects may be observed on other tissues, especially the 

 liver and kidney, and these eff'ects, although not involved in the production 

 of diabetes, are of interest in connection with the mechanisms of alloxan 

 action. 



Description of Islet Changes 



The cytological changes observed are reasonably uniform in many species. 

 The following summary is taken mainly from Dunn et al. (1943 b), Lukens 

 (1948), and Lazarus et al. (1962). The rapidity with which visible changes 

 in the /5-cells can be induced by alloxan injections is remarkable. Within 

 5 min there is a diminution of cytoplasmic and nuclear granules, the cyto- 

 plasm becoming more homogeneous or foamy, and this is accompanied by 

 a shrinkage of the cells. These changes proceed and by 15-30 min the cyto- 

 plasm is clearer, the cells more shrunken, and the nuclei are slightly pyc- 

 notic. Tiny vacuoles can now be observed in the cytoplasm and these 

 grow and coalesce until the cells are mainly vacuolated. Nuclear pycnosis 

 also progresses with chromatin clumping and eventual disintegration of 

 the nuclear membrane between 5 and 10 hr after administration of the 

 alloxan. By 24 hr the /5-cells are mainly destroyed and the islets contain 

 cellular debris and within 3-5 days no /5-cells may be visible, although the 



