Target organ specificity of major neuropeptide stimulants in locust excretory systems

The major stimulant of ileal fluid reabsorption in Locusta migratoria and Schistocerca 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 combination with locustakinin (Lom-K) or Locusta-diuretic hormone (Locusta-DH). Stimulants 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)) or the rate of fluid reabsorption across S. gregaria ilea and recta in vitro. Thus, hormonal control of these major organs of the excretory system appears to be clearly separated. Lom-K and Locusta-DH acted synergistically to stimulate secretion by S. gregaria Malpighian tubules, and the diuretic response was more rapid than the response of the ileum and rectum to hindgut stimulants. 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.