Comparative effects of GLP-1-(7-36) amide, oxyntomodulin and glucagon on rabbit gastric parietal cell function

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Abstract

We have investigated in vitro, the effects of glucagon-like peptide-1-(7-36) amide), oxyntomodulin and glucagon on two rabbit parietal cell-enriched fractions (F3, F3n), with parietal cell contents of 60% and 88%, respectively. Histamine (10−5 M) stimulated [14C]aminopyrine accumulation to an amount of 850% in excess of the basal level, whereas GLP-1-(7-36) amide (10−7 M) and oxyntomodulin (10−6 M) induced increases of 50% and 30%, respectively. With a histamine concentration of 10−6 M, [14C]aminopyrine accumulation was stimulated to 498% in excess of the basal level; GLP-1-(7-36) amide (10−7 M) and oxyntomodulin (10−7 M) induced increases of 50% and 15%, respectively. With these parameters, oxyntomodulin[19-37] and glucagon were without effect. Specific binding of [125I]GLP-1-(7-36) amide to parietal cell plasma membranes was inhibited dose-dependently by GLP-1-(7-36) amide, oxyntomodulin and glucagon with inhibitory concentrations of 0.25 nM, 65 nM and 800 nM, respectively. No specific binding of [125I]oxyntomodulin or [125I]glucagon was detectable. GLP-1-(7-36) amide receptor mRNA was only detected in parietal cell-enriched fractions. GLP-1-(7-36) amide, oxyntomodulin and glucagon stimulated parietal cell cAMP production to similar maximal levels with median values close to 0.28 nM, 10.5 nM and 331.7 nM, whereas oxyntomodulin[19-37] had no effect. The maximal cAMP production induced by GLP-1-(7-36) amide, oxyntomodulin or glucagon was additive to that induced by histamine. Our data demonstrate the presence of a GLP-1-(7-36) amide receptor in rabbit parietal cell coupled to the cAMP pathway and the interaction of oxyntomodulin and glucagon with this receptor. The results argue in favor of a cAMP compartment coupled to the GLP-1-(7-36) amide receptor, different from that involved in histamine-induced [14C]aminopyrine accumulation.

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