Mast cell maturation in young rats: a histofluorescence and cytochemical study.

Since they are not submitted to experimental alterations new-born rats are useful for the investigation of mast cell maturation and were therefore analysed in the present study. In the mesentery of new-born rats immature mast cells were present within and close to fat sheaths containing blood vessels. On day 15, mast cells were also found in mesentery windows and generally in a more advanced stage of maturation. On day 30, the distribution and maturation of mast cells were similar to those found in adult rats. In new-born rats, immature mast cells contained a few metachromatic granules, which showed a positive fluorescence after berberine sulfate staining for heparin and after exposure to paraformaldehyde for serotonin detection. Orthophthaldialdehyde-induced fluorescence for histamine demonstration was negative. On day 15, heparin and serotonin fluorescence were increased and histamine fluorescence became positive. Electron microscopically most mesentery immature mast cells of new-born rats had a well developed Golgi apparatus and rough endoplasmic reticulum, numerous mitochondria and an indented nucleus. The few cytoplasmic granules were large and some of them showed a positive trimetaphosphatase reaction in their periphery. On day 15, most mast cells were almost full of granules. On day 30, mast cells could not be distinguished from those in adult rats. These results show that mast cell maturation in young rats differs from that in adult animals after peritoneal distilled water injection.