Objectives and methods: Sorbin, a peptide isolated from porcine intestine and composed of 153 aminoacids, has been purified because its specific action is to increase water and ion absorption in the intestine and the gall bladder. We showed that synthetic peptides containing the amidated C-terminal part of sorbin had the same activity as the natural molecule in increasing duodenal absorption. In order to characterize the site of action of sorbin, the effect of two C-terminal derivatives were determined in ileal ligated loops in situ in anaesthetised rats, following VIP-induced water and electrolyte secretions. Their effect was compared to those of metenkephalinamide, NPY and somatostatin. Unidirectional fluxes were studied to analyze the mechanism of action of sorbin, by means of 22Na, administered into the intestinal loop, and 36Cl, injected into blood.
Results: Results show that C20-sorbin and C7-sorbin decreased the VIP-stimulated net flux of water (inhibition of 40 and 37%, respectively), Na (inhibition of 31 and 30%), C1 (inhibition of 80 and 63%) and HCO3 (inhibition of 15 and 25%). These effects are evidently greater than those produced by equimolar doses of NPY, somatostatin, and 32 times higher dose of metenkephalinamide. Sorbin acts as a potent anti-secretor, anti-VIP, in rat ileum.