PHARMACOLOGICAL STUDY OF THE 2ND MESSENGERS THAT CONTROL RECTAL ION AND FLUID TRANSPORT IN THE DESERT LOCUST (SCHISTOCERCA-GREGARIA)

The involvement of second messengers in modulating Schistocerca gregar ia rectal ion and fluid transport was investigated using two in vitro bioassay systems: everted rectal sacs and rectal flat sheets. Various agents known to block or activate specific signal transduction pathway s were employed in these bioassays. Cyclic AMP stimulated rectal fluid reabsorption (J(v)) and Cl- transport (I-sc) to the same extent as aq ueous extracts of corpus cardiacum storage lobes. Cyclic GMP also part ially (50%) stimulated both rectal J(v) and I-sc. Exogenous Ca2+ was n ot required for the maintenance of rectal transport, indeed Ca2+ free conditions increased the amount of stimulatable J(v). There was some e vidence indicating intracellular Ca2+ may play a minor role in control ling rectal transport. The phospholipase C mediated signal transductio n pathway was not involved with the stimulation of rectal transport, a nd appeared to have an inhibitory role. Neuroparsins, antidiuretic neu ropeptides from Locusta migratoria, showed no activity upon either S. gregaria rectal ion or fluid transport. The findings of this study sho w that the two closely related insects possess discrete antidiuretic f actors which stimulate rectal transport via different signal transduct ion pathways. (C) 1996 Wiley-Liss, Inc.