THE MAST CELLS 



One of the most active disintegrators of the rat's mast cells was found in 

 d-tubocurarine in lethal dosage, which, as Schild and Gregory (1947) have 

 shown, can also liberate histamine. Following slow injection of 5 mg. 

 d-tubocurarine chloride (Duncan), not only is it difficult to find a mast cell 

 in the peritoneal spreads but there is also extensive oedema and associated 

 degranulation of mast cells in the subcutaneous tissue. 



Histamine 



In an attempt to distinguish between the effects on mast cells of histamine- 

 liberators and the histamine which is liberated, rats were injected intravenously 

 with 1 ml. doses of histamine dihydrochloride (British Drug Houses) in 

 concentrations ranging from 1 in 100,000 to 1 in 5. Only with the highest 

 concentrations were gross changes observed in the mast cells, and these only 

 in the areas of vasodilatation and tissue oedema produced by the histamine, 

 especially in the peritoneum. None of the mast cells showed gross vacuolation. 



Non-specific oedema 



Some years ago it was found that the application of a light venous tourniquet 

 to the hind limbs of mice was followed within twenty-four hours by an almost 

 complete disappearance of mast cells from the oedematous skin (Drennan and 

 Riley, unpublished observation). Since then Drennan (1951) has studied 

 human skin in a state of oedema and found there also a similar disappearance 

 of mast cells. The use of histamine, mentioned above, may thus have brought 

 about its effect on the mast cells by the production of a local oedema rather 

 than directly. It was decided therefore to produce a local oedema by other 

 methods. 



Local oedema was produced in rats by (1) scalding one side of the back, 

 under anaesthesia, with water at 95° C, or (2) heating the area for thirty 

 minutes with an infra-red lamp. In these areas of local oedema of the under- 

 lying subcutaneous tissue there is obvious degranulation of the tissue mast 

 cells. In the oedematous zone due to scalding many of these cells have a homo- 

 geneous 'glassy' appearance as if the granule substance had run together, 

 and in some of them occasional irregular vacuoles are also present. The 

 degranulating effect is seen only in the area rendered oedematous; there is no 

 effect, for example, on the peritoneal cells remote from the oedematous area. 



It may be concluded then that the local degranulation of mast cells in areas 

 of oedema is different in quantity and in quality from the widespread vacuola- 

 tion and disruption of mast cells which follow the injection of a histamine- 

 liberator. However, if the liberator is injected slowly, there will be time for 

 both processes to occur and a mixture of effects will be seen. 



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