The distribution and myotropic activity of locustatachykinin-like peptidesin locust midgut

The midgut of the African migratory locust, Locusta migratoria, was found t o contain endocrine-like cells that stained positively for locustatachykini n I (Lom TK I)-like immunoreactivity. These cells were distributed in an un equal manner throughout the midgut of the locust, with a greater density of Lom TK I-like immunoreactive endocrine-like cells occurring in the posteri or region of the midgut. These singly occurring cells appear elongate with an apical extension projecting toward the midgut lumen and a smaller projec tion extending towards the midgut basal lamina. No immunoreactive neuronal processes were detected along the midgut wall. Radioimmunoassays revealed t hat the female midgut contained two to three times more Lom TK I-like mater ial than the male midgut, and radioimmunoassay coupled to high-performance liquid chromatography analysis revealed that at least five locustatachykini n isoforms appear to be present in the midgut. This distribution of Lom TK I-like material suggests possible functional differences in the various reg ions of the midgut. The role that these cells may play in locust midgut sec retory activity and motility remains unknown. However, the addition of synt hetic Lom TK I through IV to a ring type midgut muscle preparation stimulat ed contraction of midgut circular muscles, suggesting a possible physiologi cal role for these peptides. Dose-response curves constructed for Lom TK I- IV revealed that the peptide-induced contractions increased in a dose-depen dent manner. (C) 1999 Elsevier Science Inc. All rights reserved.