Journal of Insect Physiology 51 (2005) 1–9 In vitro analysis of the digestive enzymes amylase and a-glucosidase in the midguts of Locusta migratoria L. in response to the myosuppressin, SchistoFLRFamide Sharon R. Hill à , Ian Orchard Department of Biology, University of Toronto at Mississauga, Mississauga, Ontario, Canada L5L 1C6 Received 21 June 2004; received in revised form 1 October 2004; accepted 6 October 2004 Abstract We have investigated the effect of the locust myosuppressin, SchistoFLRFamide, on the activity of amylase and a-glucosidase in the midgut of 2-week old male locusts. Total enzyme activity in the lumen contents and tissue extracts of midguts responds to SchistoFLRFamide in a dose-dependent manner that appears to vary with the feeding state of the locust and duration of exposure to the peptide. Starvation for 24h prior to assessment alters the distribution of enzyme activity between the midgut lumen contents and tissue extracts in response to SchistoFLRFamide when compared with fed locusts. Duration of exposure to SchistoFLRFamide also alters the distribution of total amylase and a-glucosidase activity; as duration of exposure increases, lower concentrations of SchistoFLRFamide increase total enzyme activity in the lumen contents while decreasing total enzyme activity in the tissue extracts. We suggest that the minimum amino acid sequence in SchistoFLRFamide necessary to increase both amylase and a-glucosidase activity is DHVFLRFamide. We have determined that two other peptides endogenous to the locust, AFIRFamide and GQERNFLRFamide, increase amylase and a-glucosidase activity in midgut lumen contents. r 2004 Elsevier Ltd. All rights reserved. Keywords: Digestion; FMRFamide-related peptides (FaRPs); Carbohydrases 1. Introduction The insect midgut has been previously described as one of the largest endocrine organs in insects (Fuse´ et al., 1999; Lange, 2001; Z ˇ itnˇan et al., 1993). The midgut contains numerous endocrine-like cells expres- sing various peptides such as FMRFamide-related peptides (FaRPs) (for review see Orchard et al., 2001), tachykinins (Pabla and Lange, 1999), and allatostatins (Sarkar et al., 2003; Fuse´ et al., 1999; Maestro et al., 1998). Endocrine-like cells have been described in the midgut of many insect species (for reviews see Z ˇ itnˇan et al., 1993; SehnalandZ ˇ itnˇ an,1996), including Locusta migratoria L. (Pabla and Lange, 1999; Lange and Orchard, 1998). These endocrine-like cells may assess midgut lumen contents and release peptides into the haemolymph in response to feeding, to act locally and/ or to be circulated to remote targets (for review see Orchard et al., 2001). Peptides, including those previously mentioned, have been implicated in altering midgut activity by eliciting a shortcircuitioncurrent,asin Manduca sexta (Leeetal., 1998) and altering digestive enzyme activity, as in the cockroach Diploptera punctata (Fuse´ et al., 1999), the coconut black headed caterpillar Opisina arenosella (Harshini et al., 2002), the scallop Pecten maximus (Nachman et al., 1997) and the red palm weevil Rhynchophorus ferrugineus (Nachman et al., 1997). Application of the cockroach myosuppressin, leuco- myosuppressin (LMS), alters a-amylase activity in the ARTICLE IN PRESS www.elsevier.com/locate/jinsphys 0022-1910/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jinsphys.2004.10.003 à Corresponding author. Tel.: +19055694752; fax: +19058283792. E-mail address: shill@utm.utoronto.ca (S.R. Hill).