Chapter 24 - Insect Diuretic and Antidiuretic Hormones

Abstract

This chapter focuses on diuretic hormones (DH) and antidiuretic hormones (ADH) present in insects. Insect DH and ADH constitute a diverse group of peptides that have in common their role in controlling fluid and ion loss via the excretory system. In the excretory process of insects, Malpighian (renal) tubules (MT) generate a flow of primary urine that is subsequently modified by reabsorptive and secretory processes in the hindgut (ileum and rectum). DH accelerates primary urine production, whereas antidiuretic hormones generally stimulate fluid reabsorption in the hindgut, although some reduce MT secretion. DH and ion transport peptide (ITP) prepropeptides contain an N-terminal signal sequence of about 20 amino acid residues followed by active and inactive peptide sequences separated by some combination of two basic amino acids. Moreover, MT fluid secretion is coupled to ion transport, and DH stimulates KCl/NaCl secretion into the lumen. This is driven by active proton transport across the principal cell apical membrane by a V-type ATPase, with secreted protons returning to the cell via cation/H+ antiporters. Schgr-ITP is the only identified ADH that stimulates fluid reabsorption from the insect hindgut and was isolated from a locust.