Parasympathetically-mediated swelling of mast cell granules during feeding.

Mesentery mast cells have been observed to swell and to spontaneously return to their original size following feeding of 12-h fasted rats. This effect may be controlled by parasympathetic efferent nerve impulses, since it is inhibited by atropine. It was reproduced in vitro in isolated rat peritoneal fluid mast cells exposed for 30s to 10(-8)-10(-11) M acetylcholine. When examined under the electron microscope, mast cell average granule diameters had increased by 29% (p less than 0.001) following treatment. Swollen granules did not leave (exocytose) acetylcholine-treated mast cells. They gradually and spontaneously returned to their original size. This recovery only differed from that occurring in the fed rat by its greater speed.