PRODUCTION AND LIFE-SPAN OF CUTANEOUS MAST-CELLS IN YOUNG-RATS

  • 1 January 1979
    • journal article
    • research article
    • Vol. 128  (MAR) , 225-238
Abstract
Tritiated thymidine was injected into young rats (age 7 days) in such a way as to be incorporated into the nuclei of cells that were synthesizing DNA during a period of 22 h. Specimens of skin from the back and the pinna of the ear were taken at intervals from 1 to 112 days after injection. The mast cells were stained with Alcian blue and autoradiographs were prepared. Nuclei were counterstained red with alum-brazilin. Making due allowance for growth of the animals and for shrinkage due to histologic preparation, the total numbers of mast cells in the dorsal skin and in the pinna were determined. The numbers of mast cells containing [3H]thymidine were calculated from the proportions of those cells found to have radioactive nuclei. Using these data, the rates of appearance of labeled mast cells and of decline in their numbers with time were determined for both regions of skin. No mitotic figures were seen in any mast cells. Mast cells arise by the division of agranular precursor cells of unknown identity. The characteristic cytoplasmic granules appear to be produced by the daughter cells during the 24-48 h following premitotic replication of the DNA of the precursors. The differentiated cells have very variable life spans, the calculated half-lives being 4-9 days in the back and 7-20 days in the external ear. All the labeled mast cells had disappeared after 28 days in the back and after 84 days in the ear. The mast cells produced early in life may have much shorter life spans than do most of the mast cells present in adult rats. The longer life span found in the pinna may account for the greater density of the cells there than in the back. This regional difference may reflect the greater need for mast cells in a region which is more susceptible to adverse environmental influences.

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