THE MAST CELLS 



Long-term experiment: Rats — dosage as for short-term experiment for 

 the first five days, thereafter single daily injections of 500 fxg. with increments 

 of 100 (j-g. every other day to reach 1 mg. per day and continuing at this level 

 of dosage once daily up to the thirty-first day of the experiment. 



Mice — dosage as for short-term experiment for the first five days, thereafter 

 single daily injections of 200 [ig. for five days, then 250 y.g. for five days, and 

 finally 300 \ig. once daily up to the thirty-first day of the experiment. 



The ears and subcutaneous connective tissue (obtained by removing the 

 skin and scraping off the tissue from the under surface) were selected for estima- 

 tion of their histamine content. This was assayed on the isolated guinea pig 

 ileum preparation in the presence of atropine or on the blood pressure of the 

 atropinized cat. Representative tissue spreads were prepared, fixed, and 

 stained with toluidine blue for mast cells as previously described. 



Results 

 Short-term experiments 



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

 100 [j-g. of compound 48,80 produces in rats shock, erythema followed by 

 cyanosis of the ears, and visible oedema in certain regions of the skin. This 

 oedema appears to be dependent on the presence of available histamine, for 

 the ears and feet are the usual sites of early swelling and these tissues are rich 

 in both histamine and mast cells. Severe itching seems to occur in both regions. 

 The amounts of histamine released by the liberator and circulating subsequently 

 in the body decrease with each injection of compound 48 80, until at day three 

 the histamine content of the ear and subcutaneous connective tissue is reduced 

 to some 3-7 per cent of its original value (Table XIV and Fig. 41). 



Table XIV 



Histamine content of tissues of rats following 



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



experiment) 



Values expressed in [J-g./g. tissue 



110 



