Endogenous Secretin in the Rat — Evidence for a Role as an Enterogastrone but Failure to Influence Serum Calcium Homeostasis

Summary

The release of secretin into plasma by intraduodenal (id) infusion of HCl or iso-osmotic (290 mosml⁻¹) NaCl, and the associated changes of moderately stimulated gastric acid, serum gastrin, two calciotropic hormones, total and ⁴⁵calcium (Ca), were examined in the rat. The possible role of endogenous secretin as an enterogastrone and as a mediator of the hypothesized endocrine gut-thyroid-parathyroid axis was further characterized with the aid of secretin immunoneutralization and exogenous secretion. The id-HCl-stimulated secretin, measured by a sensitive radioimmunoassay, was accompanied by a decrease in gastric acid secretion, whereas secretin blockage by anti-secretin immune serum resulted in a significant increase in acid secretion. The correlation between plasma secretin and acid output was only slight. Gastrin and Ca metabolism remained unchanged during secretin stimulation. Intravenous synthetic porcine secretin at a dose reported to be effective in other target preparations (2 CU (0.58 μg) kg⁻¹ h⁻¹) had no effect on gastric acid secretion and Ca metabolism. In contrast, a pharmacological dose, 32 CU (9.3 μg) kg⁻¹h⁻¹, inhibited acid secretion, decreased serum Ca and total protein, and increased serum parathyroid hormone, but left calcitonin and gastrin unchanged. Endogenous secretin appeared to act as an enterogastrone, but whether it was the only one is unclear. No role was detected for secretin in the gut-thyroid-parathyroid axis, since the Ca changes observed may have been unspecifically mediated.

Key words

Intraduodenal infusion - Endogenous secretin - Gastric acid - Calcium metabolism - Exogenous secretin