Fluid secretion by single isolated Malpighian tubules of the house cricket, Acheta domesticus, and their response to diuretic hormone

Abstract

ABSTRACT. A simple modification of the Ramsay method is described for the isolation in vitro of Malpighian tubules from Acheta domesticus. Isolated tubules continue to secrete for many hours in a simple Ringer solution. The rate of secretion is linearly related to the length of tubule within the bathing fluid.Secretion rates during the immediate post‐equilibration period relate to the physiological state of the donor insect. Highest rates are recorded in tubules removed from animals during the scotophase when the crickets are most actively feeding. Starvation reduces the rate of secretion and when previously starved insects are given access to food the rate increases. These results are consistent with variations in the haemolymph titre of DH that are induced by feeding.Tubule fluid secretion is stimulated by either CC extract (1 gland pair/50 μ1) or dibutyryl cAMP (10‐3M). CC extracts increase the rate of fluid secretion by c. 200 pl/mm/min for up to 6 h after the tubules have been isolated. The response varies little with the age or physiological state of the donor insect. However, tubules from newly moulted insects secrete at very low rates and respond poorly to CC extract, although they are stimulated by cAMP. The significance of these results is discussed with particular reference to the use of Acheta tubules as a bioassay preparation for DH.