9604394 Beyenbach The function of insect kidneys is remarkable in that urine is produced entirely by secretory mechanisms and not by filtration as in human kidneys. Secretion is regulated by hormones such that the insect is neither under- nor over-hydrated. One recently discovered hormone, Culex-diuretic peptide, protects the insect against over-hydration, particularly important for blood-feeding insects. Taking a blood-meal, the mosquito takes on a payload more than twice its own body weight threatening flight with disastrous consequences were it not for extremely fast processing of the meal. Astonishingly, much of the ingested blood is digested, absorbed and excreted from the kidney while the meal is still in progress with the effect of urinating on the host from mne end while sucking blood from the other end, adding insult to injury. Doing so, the mosquito gets rid of the unwanted salt, water and weight of the blood meal and then flies away keeping sugars, fats, and proteins for its own use. High rates of salt and water transport in the kidney apparently are triggered by the hormone Culex-diuretic peptide which stimulates transport through the cells of the kidney and, surprisingly, also between the cells of the kidney! Transport between the cells of kidney and its regulation by a hormone is a new phenomenon in biology with potentially important lessons for our understanding of tranpsort functions in all epithelia, from kidney to intestine, stomach, pancreas, and secretory glands. Potential biomedical and clinical applications of understanding the mechanism and regulation of epithelial transport between cells cannot be denied.
