In order to examine the relationships between gut somatostatinlike immunoreactivity and gastrin, we studied the regulation of their secretion from isolated perfused extrinsically denervated rat gut preparations by bombesin nonapeptide and carbamyl choline. Carbamyl choline inhibited somatostatinlike immunoreactivity and stimulated gastrin secretion in a dose-dependent fashion with maximum responses at 10-6 M. These effects of carbamyl choline were abolished by atropine but not by hexamethonium. Conversely, bombesin nonapeptide stimulated both somatostatinlike immunoreactivity and gastrin secretion in doses as low as 10-10 M for somatostatinlike immunoreactivity and 10-9 M for gastrin. Neither atropine nor hexamethonium influenced bombesin-stimulated gastrin release but both agents abolished bombesin-stimulated somatostatinlike immunoreactivity secretion. The combination of carbamyl choline and bombesin affected somatostatinlike immunoreactivity and gastrin secretion in an identical fashion as carbamyl choline alone. These results suggest that somatostatinlike immunoreactivity and gastrin secretion from the gut are differentially regulated. Carbamyl choline stimulates gastrin release and inhibits somatostatin release by activation of muscarinic cholinergic receptors. Bombesin stimulates somatostatin release by activation of neural pathways involving both nicotinic and muscarinic cholinergic receptors. However, stimulation of gastrin release by bombesin does not involve cholinergic neural pathways and may reflect a direct action on gastrin cells.
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