Effect of β-casomorphins on somatostatin release in dogs

In the present study, the effects of orally administered β-casomorphins (β-CM) and met-enkephalin on postprandial plasma somatostatin-like immunoreactivity (SLI) were assessed in conscious dogs. The intragastric instillation of a liver extract-sucrose test meal containing 12 mg β-CM or 10 mg metenkephalin, respectively, augmented the postprandial rise of peripheral vein plasma SLI levels significantly. This effect was inhibited by the additional administration of the specific opiatereceptor antagonist, naloxone. When liver extract-sucrose was dissolved in fresh bovine milk the increase of plasma SLI levels was significantly greater than liver extract-sucrose dissolved in water. This milk-induced augmentation of SLI levels was also reduced by naloxone. Since these opiate-active compounds have an influence upon insulin release when given iv, the effect of β- CM-7, β-CM-5, β-CM-4 β-CM-4-amide, and met-enkephalin on SLI levels was assessed during their iv infusion at a rate of 1 nmol/kgh during an iv background infusion of a glucose-amino acid mixture. The infusion of β-CM-5 elicited a stimulation of peripheral vein SLI levels, whereas the infusion of met-enkephalin resulted in a significant decrease of SLI levels. β-CM-7, β-CM-4, and β-CM-4-amide had no effect on plasma SLI levels at the dose employed. The present data demonstrate that in dogs the ingestion of opiate-active peptide stimulates postprandial SLI release, indicating that nutrient-contained opiate-active material (exorphins) might participate in the regulation of postprandial gastrointestinal endocrine function.