On the 48/80-induced secretion of tissue mast cells and its mitogenic effect on nearby cells in the intact rat.

Histamine release from tissue-bound mast cells and cell proliferation in the proper mesentery in the intact rat was quantitated following in intraperitoneal injection of graded doses of compound 48/80. The dose-response curves were sigmoid-like in linear-log plots. ED50 for histamine release was 0.035-0.040 and for increased cell proliferation 0.040-0.048 microgram per g BW. The proliferative response following mast-cell secretion ceased after a period of between 48-72 h, irrespective of whether a high or a low dose of 48/80 was used. Basal on the net rate of histamine synthesis (ca. 0.45 microgram/g mesentery wet weight/h) after an initial injection of 48/80, on the extent of histamine release and the proliferative response after a repeated injection of 48/80, it is concluded that there is a lag period of at least 3 days before proliferation can be re-stimulated by renewed 48/80-induced mast-cell secretion.