MAST CELLS AND HISTAMINE IN SKIN 



tumour that my attention was distracted for the time being from our previous 

 finding of an unusually high 5-HT content in the dermis of precancerous 

 mouse skin. Biological assay for 5-HT in all the material was confirmed by 

 chromatography of tissue extracts. On carrying out one of the routine tests 

 for 5-HT on paper (examination in ultra-violet light following treatment of 

 the spot with formaldehyde) I was confronted with the same kind of golden- 

 brown fluorescence that I had seen, years before, in the mast cells of precancerous 

 mouse skin. At that time I had followed the method recommended by Cramer 

 and Simpson (1944) which includes a preliminary fixation of the skin in 10 per 

 cent formaldehyde prior to cutting frozen sections. If no formaldehyde is 

 used no fluorescence develops. Moreover, much of the precursor substance 

 responsible for the fluorescence in the skin can be extracted from the mast cells 

 by a prolonged immersion of the tissue in acetone (Riley, 19586). This is the 

 method used for the extraction of 5-HT. According to Barter and Pearse 

 (1955) the fluorescent substance itself (which is normally demonstrable only in 

 the cells of the enterochromaffin system) is a fi-carboline derivative of 5-HT, 

 in which a third ring is formed through cyclization of the side chain. 



The histological appearances suggest that the abnormally high concentra- 

 tion of 5-HT in the dermal mast cells of precancerous mouse skin may be 

 derived, directly or indirectly, from the hyperplastic epidermis itself, and more 

 especially from the epithelial cells of the abnormal hair follicles which have 

 borne the brunt of the initial application of the carcinogen. Further, I believe 

 it is from such cells that many of the malignant epitheliomas ultimately arise. 

 The full significance of this interesting reaction in the skin of mice has yet to 

 be determined (Riley, 1959). 



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