Tachykinins: effects on gastric secretion and emptying in rats

To test the effects on gastric acid secretion and gastric emptying of non-mammalian (eledoisin, physalaemin, kassinin), mammalian (substance P. neurokinin A, neurokinin B) and synthetic tachykinins (septide, senktide), intracerebroventricular injections of these peptides were given to conscious pylorus-ligated rats (gastric secretory study) or to animals fed with a phenol red meal (gastric emptying study). The tachykinins able to cause central inhibition of acid output were those active on NK2 and NK3 receptors (eledoisin, kassinin, neurokinin A, neurokinin B and senktide). Tachykinins active on NK1 receptors (substance P. physalaemin and septide) were devoid of this activity. The most potent inhibitor was the synthetic NK3 agonist, senktide. All tested natural tachykinins significantly inhibited gastric emptying, the most potent being those active on NK2 receptors. Septide, the synthetic NK1 agonist, had lowest effect and senktide, the synthetic NK3 agonist, was far less active than eledoisin, kassinin and neurokinin A. Thus, specific tachykinin receptors exist in the rat brain that mediate gastric functions: NK3 receptors participate in the control of gastric secretion, while NK2 receptors seem to be involved in the regulation of gastric emptying by activating inhibitory pathways.