Fanciulli, Giuseppe and Dettori, Alessandra and Demontis, Maria Piera and Tomasi, Paolo and Anania, Vittorio Domenico and Delitala, Giuseppe (2005) Gluten exorphin B5 stimulates prolactin secretion through opioid receptors located outside the blood-brain barrier. Life Sciences, Vol. 76 (15), p. 1713-1719. ISSN 0024-3205. Article.
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Gluten exorphin B5 (GE-B5) is a food-derived opioid peptide identified in digests of wheat gluten. We have recently shown that GE-B5 stimulates prolactin (PRL) secretion in rats; this effect is abolished by preadministration of the opioid receptor antagonist naloxone. However, since the structure of naloxone allows it to cross the blood-brain barrier (BBB) and antagonize opioid effects centrally as well as peripherally, it could not established, on the basis of those data, if GE-B5-induced PRL release is exerted through sites located inside or outside the BBB. In this study, we sought to determine the site of action of GE-B5 on PRL secretion, by pretreating male rats with naloxone methobromide (NMB), an opioid antagonist that does not cross the BBB. Four groups of rats were given the following treatments: 1) intravenous vehicle; 2) intravenous GE-B5 (3 mg kg−1 body weight); 3) intraperitoneal NMB (5 mg kg−1 body weight), followed by vehicle; 4) NMB, followed by GE-B5. Blood samples for PRL were taken at intervals for 40 minutes after vehicle or GE-B5 administration. GE-B5 stimulated PRL secretion; the effect was statistically significant at time 20. NMB preadministration completely abolished PRL response. Our experiment indicates that GE-B5 stimulates PRL secretion through opioid receptors located outside the BBB. Since opioid peptides do not exert their effect on PRL secretion directly, but via a reduced dopaminergic tone, our data suggest that GE-B5 can modify brain neurotransmitter release without crossing the BBB.
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