The effects of FMRFamide-related peptides on an insect ( Locusta migratoria) visceral muscle

Abstract

We have examined the effects of a number of FMRFamide-related peptides on the contraction of locust oviducts. SchistoFLRFamide (PDVDHVFLRFa) and leucomyosuppressin (pQDVDHVFLRFa) both decrease the amplitude and frequency of myogenic contractions and reduce basal tension. Leucomyosuppressin also reduces the amplitude of proctolin-induced contractions, an effect previously shown for SchistoFLRFamide. In contrast to these inhibitory effects, other FMRFamide-related peptides stimulate contractions of locust oviduct. Thus, removal of the amide, as in SchistoFLRF, shortening of the peptide, as in FLRFamide and FMRF, or altering the N-terminal extension, as in YGGFMRFamide or TNRNFLRFamide, result in peptides which stimulate contraction, although at concentrations which are quite high. The requirements for inhibition lie in a C-terminal amidation and a specific N-terminal extension similar to PDVDHV or pQDVDHV. The results suggest the presence of at least two receptor types for FMRFamide-related peptides. One receptor type leads to inhibition of contraction whereas the other leads to stimulation of contraction. The direct neural control of locust oviducts and neurohormonal control by FMRFamide-related peptides is discussed.