Submitted to: Peptides
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/1999
Publication Date: N/A
Interpretive Summary: Because of problems with the development of resistance to conventional pesticides, there is a critical need for new concepts and alternative approaches in controlling such pests. The basic premise of this research is that peptides (short chains of amino acids) serve as potent internal messengers in insects to regulate vital functions. Peptides themselves are eunsuitable for control measures due to their instability to enzymes in the circulatory and digestive systems of the insect. New, selective control measures may be developed by designing metabolically stable mimics of these neuropeptides that actively inhibit or over-stimulate functions regulated by them, resulting in disruption of the internal environment of the insect. One of the important pieces of information required to develop neuropeptide-based pest control strategies is to determine the effects of the natural neuropeptides on critical bodily functions and/or behavior. In nthis paper, we describe for the first time that neuropeptides of the allatostatin class stimulate in potent fashion the release of digestive enzymes that metabolize carbohydrates in an insect. This work suggests that this class of neuropeptides can modulate aspects of digestion, and that mimics designed to resist the inactivation by natural forces that degrade the natural neuropeptides could disrupt this critical process in pest insects. This work leads us one step closer to the development of practical neuropeptide-like chemicals that will be effective in controlling certain pest insects in an environmentally friendly fashion.
Technical Abstract: Neuropeptides of the cockroach allatostatin (AST) family are known for their ability to inhibit the production of juvenile hormone by the corpora allata of cockroaches. Since their discovery, they have also been shown to modulate myotropic activity in a range of insect species as well as to act as neurotransmitters in Crustaceans and possibly in insects. The midgut of cockroaches contains numerous endocrine cells, some of which produce AST whereas others produce the FMRFamide-related peptide, leucomyosuppressin (LMS). We have determined if ASTs and LMS are also able to influence carbohydrate-metabolizing enzyme activity in the midgut of the cockroach, Diploptera punctata. Dippu-AST 7 stimulates activity of both invertase and alpha-amylase in a dose-dependent fashion in the lumen contents of ligatured midguts in vitro, but not in midgut tissue. Leucomyosuppressin also stimulates enzyme activity in lumen contents only, although the 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. Thus, in this organ, AST and LMS have at least two distinct physiological effects.