The physiological significance of putative diuretic factors in the yellow fever mosquito, Aedes aegypti

Abstract

The post blood meal diuresis in the mosquito may be regulated by neuroendocrine factors. Two families of neuropeptides, the diuresins and the leucokinins stimulate fluid secretion in Malpighian tubules of several insects. Recently, several new peptides have been isolated and synthesized from both families of neuropeptides. A putative diuresin-like diuretic factor has been purified and sequenced from Culex salinarius. Several leucokinins have been isolated from two species of mosquitoes, the culekinin depolarizing peptides (CDP-I, II and III) isolated from C. salinarius and Aedes leucokinin peptides (ALP-I, II and III) isolated from Aedes aegypti. The three major objectives of this work were: (1) to examine the effect of 5-hydroxytryptamine (5-HT), the mosquito diuresin and the mosquito leucokinins on urine production in vivo in the mosquito A. aegypti, (2) to inhibit the biological effects of ALP-I and C. salinarius diuresin with antibodies raised against these peptides, (3) to determine if biologically active peptides increased Malpighian tubule intracellular second messengers 3',5'-cyclic adenosine monophosphate (cAMP) and or inositol 1,4,5-trisphosphate (IP3 This study has demonstrated that putative diuretic factors from two families of insect neuropeptides and 5-HT influence Malpighian tubule function. The mosquito diuresin, leucokinins and 5-HT stimulated total urine production in a dose dependent manner. A significant inhibition of peptide-stimulated urine production occurred following immunization with either ALP-I or C. salinarius diuresin antibodies. The C. salinarius diuresin significantly (p 0.05) increased intracellular cAMP concentrations in A. aegypti tubules. Stimulation of A. aegypti tubules with either CDP-II or 5-HT resulted in significant increases in both intracellular cAMP and IP3 concentrations. All of the mosquito leucokinins, with the exception of CDP-I, significantly increased intracellular IP3 in tubules. Data presented here suggest that the mosquito leucokinins may function on the Malpighian tubules of A. aegypti by increasing intracellular Ca²⁺ through the release of IP3 sensitive intracellular Ca²⁺ stores.