Gastric acid secretion in non-mammalian vertebrates is generally stimulated by acetylcholine (ACh), bombesin/gastrin releasing peptide (GRP) and gastrin, however, in teleosts gastrin is inhibitory. Catecholamines, vasoactive intestinal polypeptide (VIP) and cholecystokinin (CCK) are inhibitory. Tachykinins and 5-hydroxytryptamine (5-HT) are stimulatory in low doses, while high doses are inhibitory. Pepsin secretion is stimulated by ACh, bombesin/GRP, caerulein, gastrin, 5-HT and tachykinins.
Bicarbonate secretion has only been studied in amphibians apart from mammals. Cholinergic agents, catecholamines, CCK, and neurotensin are stimulatory, and somatostatin inhibitory. Mucus secretion has been studied in mammals only.
Nerves immunoreactive to a number of putative neurotransmitters are found in the non-mammalian pancreas; of these VIP has been found to stimulate exocrine secretion.
Salt secretion is stimulated by VIP in both birds and elasmobranchs. ACh stimulates the bird salt secretion. Bombesin/GRP and somatostatin inhibits the elasmobranch salt secretion.