Serum Prolactin Levels after Administration of the Alimentary Opioid Peptide Gluten Exorphin B4 in Male Rats

Abstract

"Gluten Exorphins are opioid peptides identified in enzymatic digests of gluten. The effects of Gluten Exorphins are still largely unknown. It has been shown that Gluten Exorphin B5 (Tyr-Gly-Gly-Trp-Leu) stimulates Prolactin secretion in male rats. In this study, we have evaluated the Prolactin response to Gluten Exorphin B4, another exorphin whose structure (Tyr-Gly-Gly-Trp) is identical to that of the NH(2)-terminal sequence of GlutenExorphin B5. To this aim, five groups of male rats were given the following intravenous treatments: vehicle, Gluten Exorphin B5 3 mg kg-1 body weight, Gluten Exorphin B4 at the doses of 3, 6 and 9 mg kg-1 body weight. At the dose of 3 mg kg-1 body weight, Gluten Exorphin B5 induced a significant increase in Prolactin levels. Gluten Exorphin B4 could not modify Prolactin secretion, even when administered at doses three times higher than those effective for Gluten Exorphin B5. The present study: (1) indicates that Gluten Exorphin B4 does not modify Prolactin secretion in male rats; (2) confirms the ability of Gluten Exorphin B5 to exert a stimulatory action on Prolactin release; (3) suggests that the presence of the carboxy-terminal leucine in Gluten Exorphin B5 is essential for its action on Prolactin secretion."

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Opioid Peptides Derived from Food Proteins: The Exorphins

Abstract

"Peptides with opioid activity are found in pepsin hydrolysates of wheat gluten and alpha-casein. The opioid activity of these peptides was demonstrated by use of the following bioassays: 1) naloxone-reversible inhibition of adenylate cyclase in homogenates of neuroblastoma X-glioma hybrid cells; 2) naloxone-reversible inhibition of electrically stimulated contractions of the mouse vas deferens; 3) displacement of [3H]dihydromorphine and [3H-Tyr, dAla2]met-enkephalin amide from rat brain membranes. Substances which stimulate adenylate cyclase and increase the contractions of the mouse vas deferens but do not bind to opiate receptors are also isolated from gluten hydrolysates. It is suggested that peptides derived from some food proteins may be of physiological importance."

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Effect of gluten exorphins A5 and B5 on the postprandial plasma insulin level in conscious rats.

Abstract

"The effect of exogenous opioid peptides, gluten exorphins A5 and B5, which were isolated from the enzymatic digest of wheat gluten, on thepostprandial insulin level were examined in rats. The oral administration of gluten exorphin A5 at a dose of 30 mg/kg w. potentiated the postprandialplasma insulin level and the effect was reversed by naloxone. The administration of gluten exorphin B5 showed a similar effect at a higher dose (300 mg/kg w). Furthermore, intravenous administration of gluten exorphin A5 at a dose of 30 mg/kg w. also stimulated the postprandial insulin release. The fact that orally and intravenously administered gluten exorphin A5 stimulates insulin release suggests that it modulates pancreatic endocrine function by the action after the absorption rather than within the the gastrointestinal tract."

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Opioid Receptor Ligands Derived from Food Proteins

Abstract:

"During the last two decades a variety of food protein fragments has been demonstrated to elicit biological effects in various in vitro or in vivo test systems. A considerable part of these bioactive peptides are opioid receptor ligands , which may be regarded as exogenous supplements to the endogenous opioidergic systems of the human organism. Most of these foodderived opioid receptor ligands are fragments of the milk proteins alpha-, beta- or kappa-casein, alpha-lactalbumin, beta-lactoglobulin or lactotransferrin; however, also wheat gluten, rice albumin, bovine serum albumin or hemoglobin, i.e. possible constituents of meat, and even a protein from spinach could be demonstrated to contain fragments behaving like opioid receptor ligands. Practically all of these compounds display opioid agonist activity; only very few of them behave like opioid antagonists. Bioactive food protein derivatives have been termed “ food hormones”, which implies that these compounds display their bioactivities when released from food constituents, i.e. from their precursor molecules due to the action of gastrointestinal enzymes. The critical point in case of food protein-derived opioid receptor ligands is that only a minority of their bioactive effects demonstrated as yet has been observed upon oral or intragastric administration of these peptides or their precursor proteins and that most of these studies have been performed in animals. Thus, in terms of “evidence-based dietary supplementation” more studies are needed to prove effects of food protein-derived opioid receptor ligands or their precursors after oral administration in humans and, moreover, to prove a benefit for the consumers organism."

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