STUDY OF THE ACTIVATION MECHANISM OF HUMAN GRF(1-29)NH2 ON RAT MAST-CELL HISTAMINE-RELEASE

Human growth releasing factor (GRF) (1-29)NH2 releases histamine from pleural and peritoneal rat mast cells by a non cytotoxic and non immun ological mechanism. Pretreatment of cells with pertussis toxin markedl y inhibits the secretion, suggesting a possible function of a Gi-prote in in the activation pathway. In order to determine the role of cAMP o n GRF mediated secretion, mast cells were preincubated with isobutylme thylxanthine (IBMX) or cholera toxin, since both drugs greatly and enh ance cAMP levels. IBMX inhibits mediator secretion while, in contrast, cholera toxin is ineffective td modify histamine release. The PKC act ivator TPA amplifies the response of mast cells to human GRF, shifting the dose-response curve to the left. The pretreatment of mast cells w ith the phosphatase inhibitor okadaic acid exerts no effect on the dos e-response function curve to GRF, The response to human GRF does not d epend on extracellular calcium, but there is a good correlation betwee n the percent of histamine released and (45)calcium uptake. The kineti c of calcium uptake is fast, maximum uptake being reached in seconds.