EFFECTS OF PROCTOLIN AND RELATED ANALOGS ON INOSITOL PHOSPHATE PRODUCTION IN THE FOREGUT OF THE LOCUST SCHISTOCERCA-GREGARIA

Proctolin (10 nM and 0.5 mu M) stimulated dose-dependent release of [H -3]inositol 1,4,5-trisphosphate ([H-3]IP3) and [H-3]inositol 1,3,4,5-t etrakisphosphate ([H-3]IP4) from locust foregut homogenates incubated in Tris buffer containing [H-3]myo-inositol. Of the other analogues te sted for agonist activity in this preparation, the order of potency wa s proctolin >[p-F-L-phenylalanine(2)]proctolin > [alpha-methyl-L-tyros ine(2)]proctolin > RYT > cycloproctolin. [N-methyl-L-tyrosine(2)]proct olin was unable to induce significant release of [H-3]inositol phospha tes. Incubation of foregut homogenates in Tris buffer containing [alph a-methyl-L-tyrosine(2)] proctolin (10 nM) significantly reduced procto lin-stimulated release of [H-3]IP3 and [H-3]IP4 by 86 and 63% respecti vely, Increasing the dose of antagonist to 1 mu M did not result in fu rther reduction of proctolin-stimulated [H-3]IP3 release although the level of [H-3]IP4 production was reduced by 89%. Cycloproctolin and th e tripeptide RYT were less potent antagonists of proctolin-stimulated [H-3]inositol phosphate release than [alpha-methyl-L-tyrosine(2)] proc tolin only causing inhibition in excess of 80% at a concentration of 1 mu M These data provide good evidence that the locust foregut contain s a proctolin receptor, which when stimulated, causes phosphatidylinos itol hydrolysis resulting in the production of the putative second mes sengers molecules IF3 and IF4.