The distribution of a kinin-like peptide and its co-localization with a CRF-like peptide in the blood-feeding bug, Rhodnius prolixus

Rhodnius prolixus, a blood-feeding hemipteran insect, ingests large meals w hich are followed by rapid diuresis to eliminate excess water and salt. In Rhodnius, serotonin and an unidentified peptide(s) [33,34] have been shown to act as neurohormonal diuretic factors. In other insects, two families of diuretic peptides. the corticotropin releasing factor (CRF)-like, and kini n peptides [9], have been identified and sequenced. Recently, we demonstrat ed the presence of a CRF-like diuretic peptide in the CNS and digestive sys tem of Rhodnius [47] using immunohistochemistry and bioassay. In this study, combining immunohistochemistry and radioimmunoassay (RIA) te chniques, we show the presence of Ieucokinin-like peptide(s) in the CNS and digestive system of Rhodnius 5th instar. Additionally, double-label immuno histochemistry demonstrates that the leucokinin-like and CRF-like peptides are co-localized in the posterior lateral neurosecretory cells of the mesot horacic ganglionic mass (MTGM) and in neurohaemal areas on abdominal nerves one and two, suggesting the possibility of co-release of the peptides into the hemolymph. Partially purified extracts of the CNS and neurohaemal tissue were tested i n vitro on Malpighian tubule secretion and cAMP assays. The factors eluting with increasing acetonitrile percentages from Sep-Pak cartridges were assa yed in the presence or absence of ketanserin, a serotonin antagonist which blocks the effects of serotonin on Malpighian tubules. The results indicate activity of serotonin and a CRF-like diuretic peptide on Rhodnius Malpighi an tubules but fail to demonstrate activity of the leucokinin-like peptide( s). The rapid diuresis following feeding is a highly coordinated event, requiri ng the moment of water and salt across the epithelial cells of the crop int o the hemolymph and from the hemolymph across the cells of the Malpighian t ubules. The urine then travels along the Malpighian tubules into the hindgu t in order to be expelled. The presence of a leucokinin-like peptide(s) in the CNS and digestive system, which co-localizes with a CRF-like peptide(s) , suggests that kinins may play a role in the rapid diuresis, although poss ibly not directly on the Malpighian tubules. (C) 2001 Elsevier Science Inc. All rights reserved.