RESUMO
The ability of several alimentary opioid peptides (exorphin C, rubiscolin-5, cytochrophi-4) and endorphins (met-enkephalin, dynotphin A(1-10), beta-neoendorphin) to change the escape reaction of the cockroaches Periplaneta americana at their placement into a hot chamber was studied. The ED50 values increasing twice the insect stay time in the hot chamber as well as duration and dynamics of the effects were determined. It has been shown that ED5 decreases statistically significantly with increase of the length of the peptide molecule and its affinity of duration of the effects and to an increase of their affinity to delta-receptors - to prolongation of the reaction (more than150 min). In the group of alimentary peptides (exorphins) the most active was a fragment of D-ribulose-1,5-biphosphate carboxylase/oxigenase rubiscolin-5 (ED5 = 386 nM per individual). This might indicate a specific ability of some plant proteins to regulate (decrease) the insect protective behavior.