PUTATIVE MECHANISM FOR GUINEA-PIG ILEUM CONTRACTION BY N-FORMYL PEPTIDES - A COMPARATIVE-STUDY OF N-FORMYL AND N-ACETYL PEPTIDES WITH THE N-TERMINAL SEQUENCE OF THE CALPAIN SMALL-SUBUNIT

N-formyl and N-acetyl peptides with the N-terminal sequence of the cal pain small subunit were prepared and their spasmogenic activity was ex amined using guinea pig ileum preparations. Sections of ileum were fou nd to contract in the presence of all N-formyl peptides used (tri- to nonapeptides and tridecapeptide) but failed to contract with N-acetyl peptides, although both N-formyl and N-acetyl peptides have chemotacti c activity, indicating that spasmogenic activity and chemotactic activ ity involve different mechanisms. A formyl peptide antagonist, Boc-Phe -Leu-Phe-Leu-Phe, suppressed contraction by formyl peptides whereas a histamine antagonist, diphenhydramine, suppressed contraction by formy l peptides as well as by histamine. In addition, formyl peptide-induce d contractions were noted after an approximately 20-sec time lag, and their profiles were bell-shaped and roughly symmetrical. On the other hand, histamine- and acetylcholine-induced contractions exhibited a mu ch shorter time lag. These data led us to conclude that contraction in duced by formyl peptides may not occur as a direct response but may be due to the histamine released from mast cells present in the tissues of the small intestine.