THE MAST CELLS 



Short-term experiment in mice. The first intraperitoneal injection of 

 50 [j.g. of compound 48 80 produces weakness and cyanosis in mice but there is 

 little evidence of severe itching. The ears display erythema but oedema is 

 slight. A second injection of the same dose of the liberator eight hours later 

 produces a similar result. Even when the dose is raised considerably (to 

 200 (i.g.), redness of the ears and general weakness are still observed but there 

 is no scratching. Biological assays indicate that the loss of tissue histamine 

 does not exceed 50 per cent in the skin of the ears or 30 per cent in the sub- 

 cutaneous connective tissue (Table XV and Fig. 41). Disruption of mast cells 

 has occurred in these regions but it is patchy in distribution, and many mast 

 cells in the ear seem to survive. 



Table XV 



Histamine content of tissues of mice following 



treatment with 48/80 over 5 days {Short-term 



experiment) 



Values expressed in [ig./g. tissue 



At day eight (three days after cessation of injections) biological assays 

 indicate that rapid recovery of tissue histamine has occurred; correspondingly 

 the histological picture shows a complete restoration of the mast cells in both 

 areas. Thus it seems that tissue mast cells in the mouse are more resistant to 

 the disruptive action of compound 48/80 than they are in the rat. 



Long-term experiments 



Long-term experiment in rats. This experiment is, in effect, an extension 

 of the short-term experiment. Despite the continued daily injections of even 

 1 mg. of the liberator there is no mortality and the clinical signs of histamine 

 release at this dose level are virtually absent. Nevertheless, regional differences 

 are seen in the mast cells, as described earlier in this book. The cells progres- 

 sively disappear from the ears (except in the nerve sheaths) and remain absent 

 thereafter. However, in the subcutaneous connective tissue, the initial dis- 

 appearance of the cells is followed by the gradual re-development of numerous 

 mast cells in the adventitia of the small blood vessels with muscle coats, until 

 by day thirty-two many of these vessels are surrounded by several layers of 



112 



