Action of the SP2-11 and SP3-11 fragments of substance P on rat peritoneal mast cells.

The ability of the SP fragments SP2-11 and SP3-11 to release histamine from rat peritoneal mast cells has been compared with that of the whole peptide. SP1-11 was found to be about 3.4 times more active than SP2-11 and about 10.4 times more active than SP3-11. The substance P antagonist [D-Pro4, D-Trp7,9,10] SP4-11 was equally effective at antagonizing the histamine releasing action of SP1-11, SP2-11 and SP3-11. Benzalkonium chloride was found to be a competitive antagonist of SP and SP3-11: the dissociation constants for the benzalkonium chloride-receptor interaction being about the same when either SP1-11 or SP3-11 was used as the agonist.