Responses of dermal mast cells to injury.

The effect on dermal mast cell numbers and degranulation of making a partial thickness skin wound on the right flank of Wistar rats was studied immediately after operation and 0.5, 1, 2, 4, 8, 16, 24 and 72 h postoperatively. An equivalent area of intact dermis on the left flank was used as a control. In the injured dermis the mean number of detectable mast cells in the experimental group immediately after making the partial thickness wound was not significantly different from the control side (P > 0.25) but it later decreased, reaching its lowest value after 2 h and increasing from 16 h to 72 h postoperatively when the final assessment was made. The possibility that the reduction in mast cell number per unit area might be an artefact resulting from increased tissue volume due to oedema was investigated and disproved. The total number of dermal mast cells in equivalent areas of the intact left flank remained unchanged throughout this period. The percentage of degranulating mast cells started rising 0.5 h postoperatively, increased gradually to reach its highest value after 2 h, remained high up to 8 h postoperatively and then decreased to reach its lowest value after 72 h. The percentage of degranulating mast cells of the intact dermis of the left flank did not alter during this period. The lack of a significant change in the control groups shows either the absence of any systemic effect or that the technique used was not sensitive enough to detect it.