Somatostatin receptors on canine fundic D-cells: evidence for autocrine regulation of gastric somatostatin

Abstract

Somatostatin is known to have inhibitory effects on the release and action of a wide variety of gut peptides. Previous studies in vivo have suggested a potential inhibitory role for somatostatin even on its own secretion. To determine whether this autoregulatory effect is the result of a direct action of the peptide on the cell that is responsible for its secretion, we examined the effect of a non-immunoreactive but biologically active analogue of somatostatin ([Leu8-D-Trp22-Tyr25]S28) on release of somatostatin-like immunoreactivity (SLI) from isolated canine fundic D-cells. We identified somatostatin binding sites with dissociation constants of 1.2 X 10(-9) and 3.8 X 10(-8) M that coenriched with D-cells. Somatostatin 14, somatostatin 28, and [Leu8-D-Trp22-Tyr25]S28 were equivalent in displacing 125I-[Leu8-D-Trp22-Tyr25]S28 from the binding sites. [Leu8-D-Trp22-Tyr25]S28 inhibited SLI release from D-cells stimulated with (DBcAMP), and pentagastrin. Pertussis toxin pretreatment prevented the inhibitory effects of [Leu8-D-Trp22-Tyr25]S28 on both SLI secretion and cAMP accumulation by on both SLI secretion and cAMP accumulation by D-cells stimulated with epinephrine and forskolin. In contrast, [Leu8-D-Trp22-Tyr25]S28 inhibition of SLI release induced by DBcAMP and pentagastrin was not altered by pertussis toxin. Our data suggest that somatostatin autoregulates its own secretion via specific receptors on D-cells. This inhibitory effect is mediated by mechanisms that are both dependent on and independent of pertussis toxin-sensitive inhibitory guanine nucleotide binding proteins.