Histamine release from mast cells of the rat.

The relative activities of 12 agents inducing anaphylactoid oedema in the paws of two types of genetically different rats have been compared with those inducing histamine release from isolated peritoneal cells. Four groups were identified - group 1 where activities were much higher in R rats than in NR rats, doses in vivo being in all cases much lower than those required in vitro; group 2 where activities were similar in the two types of rat, doses in vivo again being relatively much lower; group 3 where activities were similar in both types of rat though doses in vivo were relatively high; group 4 where activities were similar in both types of rat, but doses in vivo were relatively extremely high. Only the activities of releasers in groups 1, 2 and 3 (represented by dextran, concanavalin A and antigen) required calcium ions in vitro and were potentiated by phosphatidyl serine; they were potentiated in vivo by insulin and inhibited by glucose.