Effects of myoinhibitory peptides on food intake in the German cockroach

Abstract

Insect myoinhibitory peptides were discovered through their inhibitory activity on visceral muscle contraction. The present study tests the antimyotropic gut properties of three galanin-related myoinhibitory peptides (Mas-MIP II: GWQDLNSAW-NH2; Grb-AST-B1: GWQDLNGGW-NH2; and Grb-AST-B3: AWRDLSGGW-NH2) in adult females of the cockroach Blattella germanica (L.) (Dictyoptera, Blattellidae). The three peptides elicit a strong inhibitory effect on both foregut and hindgut contractions, with ID50 values in all the cases within the nanomolar range. In addition, the modulatory effects of these three peptides on food intake are studied on previously starved female cockroaches. The results show that Grb-AST-B3 is the most active peptide, inhibiting food intake by 60-80% at doses between 15 and 50 μg, followed by Grb-AST-B1 (45% inhibition of food intake at the 50 μg dose), whereas Mas-MIP II is inactive even at the 50 μg dose. The differences between the three peptides may be due to a differential effect of their structure on activity or to a differential degradation. These results show that myomodulatory gut activity in vitro and antifeeding effects do not always correlate. © 2006 The Authors.Financial support from the Ministry of Science and Technology, Spain (project AGL2002-01169); and the Generalitat de Catalunya (2001 SGR 003245) is gratefully acknowledged.Peer Reviewe