PHYSIOLOGICAL ACTION OF A NEUROPEPTIDE FROM THE CORPORA-CARDIACA OF THE FRUIT BEETLE, PACHNODA-SINUATA, AND ITS POSSIBLE ROLE IN-FLIGHT METABOLISM

Various effects of a corpus cardiacum extract from the fruit beetle, P achnoda sinuata, and its synthetic peptide, were analysed. Neither the corpus cardiacum extract nor the synthetic peptide exhibited myotropi c or diuretic activity. The synthetic peptide, however, increased the haemolymph carbohydrate concentration in a dose- and time-dependent ma nner. Since the haemolymph volume is 150 mu l, injection of 20 pmol of the synthetic peptide, equalling 1.3 x 10(-7) M, was needed for a max imal response, manifested at 120-180 min. It was the disaccharide treh alose which increased after injection; it constitutes over 98% of the haemolymph's oligosaccharides during rest and after injection. Injecti on of synthetic peptide did not affect the haemolymph lipid concentrat ion or the levels of proline and alanine, During flights of 15 min dur ation, the haemolymph trehalose concentration, as well as the level of proline, decreased substantially, whereas the level of alanine increa sed. Whereas the concentration of the free amino acids returned to pre flight levels during a 1 h rest period after flight, trehalose levels did not reach preflight levels. These results indicate that hormonal r egulation of amino acid metabolism may take place. As shown by HPLC an alyses, the corpus cardiacum peptide can be released in vitro upon Ca2 +-dependent depolarization, although no release in vivo has yet been d emonstrated.