1. Schistocerca gregaria ion-transport peptide (Scg-ITP), a neuropeptide isolated from locust corpora cardiaca, stimulates ileal Cl- transport (Isc) in a dose-dependent manner and causes increases in Na+, K+ (IK) and fluid reabsorption (Jv) as previously observed with crude extracts of corpus cardiacum and with cyclic AMP. Unlike cyclic AMP, Scg-ITP does not stimulate ileal NH4+ secretion. 2. H+ secretion (JH) in the ileum, which is not affected by cyclic AMP, is almost completely abolished by Scg-ITP. Although ITP may act via cyclic AMP as second messenger to stimulate NaCl, KCl and fluid reabsorption, it apparently acts through a different intracellular pathway to influence JH. 3. Scg-ITP is unlikely to be the chloride transport stimulating hormone previously reported to act on the rectum, because it did not produce a maximum rectal Isc response and had no effect on either rectal Jv (which is Cl--dependent) or IK.

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