Inflammation and Related Phenomena 117 



The inhibitory action of monoamine oxidase inhibitors on the 

 inflammatory reaction is abolished by administration of dibena- 

 mine and similar compounds that inactivate adrenaline and re- 

 lated amines. Moreover, the action of monoamine oxidase in- 

 hibitors is potentiated by bretylium tosylate, a substance that 

 augments the effects of circulating adrenaline. In addition, the 

 effects of monoamine oxidase inhibitors on inflammation can be 

 reproduced by injection of adrenaline although not of nor-adrena- 

 line or 5-H.T. Finally, the effects of monoamine oxidase inhibitors 

 are not abolished by prior adrenalectomy (Spector and Willough- 

 by, 1960b) or hypophysectomy (Setnikar et al., 1959) . These re- 

 sults indicate that following injury, adrenaline-like substance and 

 oxidase may be brought into contact. As a result, the vasocon- 

 strictor amine may be destroyed, and inflammation allowed to 

 proceed. It seems possible that in the wall of the normal small 

 blood vessel, adrenaline-like and histamine-like compounds com- 

 pete for receptor sites, the interplay of their actions making for 

 normal vascular reactions. In inflammation, not only are the vaso- 

 dilator forces greatly augmented (as described above) but the 

 vasoconstrictor forces may be inactivated. The enzymic inactiva- 

 tion of the adrenaline-like substance could be precipitated either 

 by local activation of monoamine oxidase or release of the amine 

 from a site inaccessible to the enzyme. 



THE MECHANISM OF INCREASED CAPILLARY 

 PERMEABILITY IN INFLAMMATION: A SUMMARY 



Figure 10 attempts to illustrate the picture of vascular events in 

 inflammation as outlined in the preceding pages. It is suggested 

 that the initial event is a release of histamine from mast cells, 

 platelets or other sources by a mechanism not yet fully understood 

 but possibly involving lytic enzymes in the mast cells. This release 

 may be prevented experimentally by previous "depletion" of body 

 histamine with the aid of repeated injections of powerful hista- 

 mine liberators such as compound 48/80. The effects of the hista- 

 mine released by injury may be prevented by administration of 

 small doses of anti-histamine drugs such as Anthisan (Xeo- 



