Abstract
In the peritoneal cavity of the adult rat mast cells at the four stages of progressive maturation (and corresponding increase of sulphation of granules) are best demonstrated in free peritoneal fluid. Of the 0.1-0.2 × 1 06 cells in the free fluid, 26% are at stage 1 of maturation (all granules are stained by Alcian blue), 24% at stage 2 (majority of granules are stained by Alcian blue, minority by safranin), 20% at stage 3 (majority of granules are safranin-positive), and 30% at stage 4 (all granules are safranin-positive). Peritoneal washings yield a mean of about 1.3-1.8 × 106 mast cells of which 16% are at stage 1, 24% at stage 2, 34% at stage 3 and 26% at stage 4. The greater number recovered by washing, compared with the number in free peritoneal fluid, suggests that a substantial number of mast cells lie on the surface of the peritoneal membranes.
In mesentery and omentum, the greatest concentration of mast cells per unit area of tissue occurs in the omental milk spots, with smaller but still substantial concentrations in the paravascular adipose zones of both mesentery and omentum. Mast cells are less numerous in the windows of the mesentery and least so in the windows of the omentum. In the milk spots of the omentum, all four stages of maturation are represented with somewhat greater accent on young (stages 1 & 2) than old cells (stages 3 & 4). Such a trend is rather more pronounced for the paravascular zones of the mesentery, but reversed for the paravascular zones of the omentum.
In the mesenteric windows, mast cells are predominantly at stage 3, whereas in the omental windows, the cells are confined to zones adjacent to the milk spots, with a somewhat greater proportion of young cells than in the adjacent milk spots.
The investigation has not permitted a firm conclusion concerning the source of the mast cells harvested by peritoneal washing—whether by migration from peritoneal membranes or by development in situ from precursors free in the peritoneal cavity.