A C-terminal aldehyde analog of the insect kinins inhibits diuresis in the housefly

The insect kinins are present in a wide variety of insects and function as potent diuretic peptides in flies. A C-terminal aldehyde insect kinin analog, Fmoc-RFFPWG-H (R-LK-CHO), demonstrates stimulation of Malpighian tubule fluid secretion in crickets, but shows inhibition of both in vitro and in vivo diuresis in the housefly. R-LK-CHO reduced the total amount of urine voided over 3 h from flies injected with 1 μL of distilled water by almost 50%. The analog not only inhibits stimulation of housefly fluid secretion by the native kinin Musdo-K, but also by thapsigargin, a SERCA inhibitor, and by ionomycin, a calcium ionophore. The activity of R-LK-CHO is selective, however, as related C-terminal aldehyde analogs do not demonstrate an inhibitory response on housefly fluid secretion. The selective inhibitory activity of R-LK-CHO on housefly tubules represents an important lead in the development of environmentally friendly insect management agents based on the insect kinins.