Effect of β-Casomorphins on Somatostatin Release in Dogs*

Abstract

In the present study, the effects of orally administered beta-casomorphins (beta-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 beta-CM or 10 mg met-enkephalin, respectively, augmented the postprandial rise of peripheral vein plasma SLI levels significantly. This effect was inhibited by the additional administration of the specific opiate-receptor 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 beta-CM-7, beta-CM-5, beta-CM-4 beta-CM-4-amide, and met-enkephalin on SLI levels was assessed during their iv infusion at a rate of 1 nmol/kg . h during an iv background infusion of a glucose-amino acid mixture. The infusion of beta-CM-5 elicited a stimulation of peripheral vein SLI levels, whereas the infusion of met-enkephalin resulted in a significant decrease of SLI levels. beta-CM-7, beta-CM-4, and beta-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.

Opioid Receptor Ligands Derived from Food Proteins

“…In rats satiety was demonstrated to be influenced by casein or casein hydrolysate [125]. In dogs, milk induced the release of somatostatin [118] and in ewes, LH secretion during the early suckling period appeared to be inhibited by milk constituents [126]. All effects observed in these animal studies were antagonizable by opioid antagonists.…”

“…However, naloxone blockade was not tested in these studies. In dogs, a naloxone-antagonizable stimulation of somatostatin [118] and insulin release [119] was observed upon intragastric bovine β-casomorphin instillation; in cows, however, insulin responses to glucose stimulation were lowered upon intra-abomasal bovine β-casomorphin infusion [120]. In rats, bovine β-casomorphin(1-7) stimulated the intake of a high fat diet upon intragastric administration of the peptide [121]; antagonization of the effect by opioid antagonists was not tested.…”

Plasma β-Casomorphin-7 Immunoreactive Peptide Increases after Milk Intake in Newborn but not in Adult Dogs

“…8-casomorphins modulate secretion of postprandial insulin (5) and somatostatin (6) in dogs and can elicit analgesia (4). In addition, these peptides alter active intestinal electrolyte transport (17).…”

Peptides du lait à activité biologique

“…Des repas similaires, à l'occasion desquels la caséopeptone était remplacée par du lait frais, provoquaient l'apparition, dans le plasma sanguin, de quantités significatives d'un composant réagissant avec une antisomatostatine (Schusdziarra et al, 1983a). L'accroissement postprandial d'insuline et de somatostatine était supprimé si de la naloxone, inhibiteur spé-cifique des oploïdes, était ajoutée au repas ou bien si des endorphines telles que la Leu et la Met-enképhaline étaient injectées par voie intraveineuse (Schusdziarra et al, 1983b).…”