PHOTODYNAMIC ACTION 713 



Holocalyx produced liver dysfunction, including icterus in the later stages, 

 it seems most likely that the photosensitization is due to a derangement 

 of phylloerythrin excretion. That photosensitization through such a 

 derangement can precede both bilirubinemia (as indicated by the van den 

 Bergh test) and macroscopic liver damage has also been established in 

 work on the toxicity of P. miliaceum (Clare and J. E. V. Simpson, unpub- 

 lished observations) . 



Poisoning by Agave lechuguilla. Mathews (1937) reported that this 

 disease of sheep and cattle involves both liver damage due to a toxic 

 saponin and photosensitivity by a pigment absorbed directly from the 

 plant. The evidence for this pigment being involved is strong, since 

 extracts in which the saponin had been inactivated in various ways pro- 

 duced photosensitivity but no liver lesions. However, in investigations 

 on another disease, produced by Nolina texana, in which apparently 

 identical liver lesions are seen, Mathews (1940) again produced photo- 

 sensitivity in rats without liver damage but this time considered that 

 the photodynamic agent was phylloerythrin, because photosensitivity 

 occurred only when chlorophyll was included in the diet. From this 

 experiment it seems possible that both A. lechuguilla and N. texana may 

 contain a substance that interferes with phylloerythrin excretion in addi- 

 tion to that responsible for the observable hepatic lesions. 



This discussion of the work on Holocalyx glaziovii, A. lechuguilla, and A^. 

 texana emphasizes the desirability of carrying out tests for phylloerythrin 

 in diseases in which photosensitivity is associated with hepatic lesions. 



Photosensitivity FoUoiving Injection of Phenanthridinium. Photosensi- 

 tization associated with liver damage and icterus has been observed in 

 cattle injected with phenanthridinium 1553 during attempts to control 

 trypanosomiasis (Bell, 1945, 1947; Stewart, 1947; Evans, 1948). No 

 attempt seems to have been made to determine whether phylloerythrin 

 is the photodynamic agent, but the reports indicate that it is. The toxic 

 effects of the drug are influenced by factors not yet properly defined, and 

 thousands of animals have been treated without ill effects — a fact that 

 suggests that phenanthridinium itself is not the photodynamic agent. 

 An unusual feature is the long delay—up to 6 weeks— between injection 

 and onset of photosensitivity. 



The rest of the diseases involving hepatogenous photosensitivity in 

 animals do not require special consideration of the photodynamic agent, 

 and therefore only brief reference is made to them here. It should not 

 be inferred that they are of minor importance, for some, such as facial 

 eczema and Tetradymia poisoning, have been responsible for serious 

 losses of livestock. 



The following list summarizes the diseases and pathological conditions 

 in which photosensitivity has been observed as an accompaniment of 

 liver dysfunction: 



