Effects of an allatostatin and a myosuppressin on midgut carbohydrate enzyme activity in the cockroach Diploptera punctata

Neuropeptides of the cockroach allatostatin (AST) family are known for thei r ability to inhibit the production of juvenile hormone by the corpora alla ta of cockroaches. Since their discovery, they have also been shown to modu late myotropic activity in a range of insect species as well as to act as n eurotransmitters in Crustaceans and possibly in insects. The midgut of cock roaches contains numerous endocrine cells, some of which produce AST wherea s others produce the FMRFamide-related peptide, leucomyosuppressin (LMS). W e have determined if ASTs and LMS are also able to influence carbohydrate-m etabolizing enzyme activity in the midgut of the cockroach, Diploptera punc tata. Dippu-AST 7 stimulates activity of both invertase and ol-amylase in a dose-dependent fashion in the lumen contents of ligatured midguts in vitro , but not in midgut tissue, whereas the AST analog AST(b)phi 2, a cycloprop yl-ala, hydrocinnamic acid analog of Dippu-AST 6, has no effect. Leucomyosu ppressin also stimulates enzyme activity in lumen contents only, although t he EC50 is considerably greater than for Dippu-AST. Dippu-AST is also able to inhibit proctolin-induced contractions of midgut muscle, and this action had already been described for LMS [18]. Thus, in this organ, AST and LMS have at least two distinct physiological effects. (C) 1999 Elsevier Science Inc. All rights reserved.