Target organ specificity of major neuropeptide stimulants in locust excretory systems

The major stimulant of ileal fluid reabsorption in Locusta migratoria and S chistocerca gregaria corpora cardiaca, ion-transport peptide (ITP), had no stimulatory action on fluid secretion by isolated Malpighian tubules of S. gregaria, nor did it have a synergistic or antagonistic effect in combinati on with locustakinin (Lom-K) or Locusta-diuretic hormone (Locusta-DH). Stim ulants of locust Malpighian tubules (Lom-K and Locusta-DH) had no action on either active transport of Cl- (measured as short-circuit current, I-sc) o r the rate of fluid reabsorption across S. gregaria ilea and recta in vitro . Thus, hormonal control of these major organs of the excretory system appe ars to be clearly separated. Lom-K and Locusta-DH acted synergistically to stimulate secretion by S. gregaria Malpighian tubules, and the diuretic res ponse was more rapid than the response of the ileum and rectum to hindgut s timulants. Taken together, these data suggest that, in the initial phase of post-prandial diuresis, urine flow will exceed fluid uptake in the hindgut , thereby allowing excess water to be eliminated.