THE EFFECTS OF MANDUCA-SEXTA DIURETIC HORMONE ON FLUID TRANSPORT BY THE MALPIGHIAN TUBULES AND CRYPTONEPHRIC COMPLEX OF MANDUCA-SEXTA

1. Manduca sexta diuretic hormone (Mas-DH) stimulates fluid secretion by adult Malpighian tubules of M. sexta, demonstrating its site of diu retic action in M. sexta for the first time. It was not possible to de velop a suitable bioassay to measure fluid secretion in larval proxima l tubules. 2. Mas-DH has an antidiuretic action on the cryptonephric c omplex of larval M. sexta because it increases fluid absorption from t he rectum. It appears that in this complex Mas-DH is acting on a Na+/K +/2Cl- co-transporter, presumably on the basal membrane of the crypton ephric Malpighian tubules, because Mas-DH-stimulated fluid absorption by the cryptonephric complex is inhibited by bumetanide or the removal of Cl-, Na+ or K+ from the haemolymph side of the tissue. This is the first demonstration of hormonal control of fluid absorption by the cr yptonephric complex. 3. Concomitant with the stimulation of fluid tran sport, Mas-DH increases the amount of cyclic AMP secreted by adult Mal pighian tubules and the cryptonephric complex. In addition, Mas-DH pro motes cyclic AMP production by the larval proximal tubules.