Naloxone-induced suppression of the behavioral manifestation of serotoninergic system hyperactivation by beta-casomorphins-7 in mice

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The effect of human and bovine beta-casomorphins-7 on the behavior of mice under conditions of 5-hydroxytryptophan (5-HT) induced hyperactivation of the serotoninergic system (head twitch test) has been studied. Intraperitoneal administration of each peptide in a dose of 1 mg/kg was shown to suppress the head twitch response in mice approximately by half (p < 0.01). This effect was completely blocked by the opioid receptor antagonist naloxone (10 mg/kg), which did not alter the behavior of mice in the head twitch test by itself. Thus, the influence of casomorphins on the serotoninergic system in vivo has been demonstrated for the first time. The role of 5-HT and opioid receptors in the mechanism of casomorphin action is discussed.

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... However, it is evident that A1 stimulates production of the enzyme DPP-4 in the rat jejunum through a nonopioid mechanism (39). It is also known that BCMs are 5-hydroxytryptamine2 (5HT2)-serotonin receptor antagonists through an unrelated mechanism (52)(53)(54). Furthermore, recent research has shown that A1 compared with A2 has implications for casein micelle structure and associated chaperone activity within the gastrointestinal system that is unrelated to opioid mechanisms (55). ...
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This is the first systematic review, to our knowledge, of published studies investigating the gastrointestinal effects of A1-type bovine β-casein (A1) compared with A2-type bovine β-casein (A2). The review is relevant to nutrition practice given the increasing availability and promotion in a range of countries of dairy products free of A1 for both infant and adult nutrition. In vitro and in vivo studies (all species) were included. In vivo studies were limited to oral consumption. Inclusion criteria encompassed all English-language primary research studies, but not reviews, involving milk, fresh-milk products, β-casein, and β-casomorphins published through 12 April 2017. Studies involving cheese and fermented milk products were excluded. Only studies with a specific gastrointestinal focus were included. However, inclusion was not delimited by specific gastrointestinal outcome nor by a specific mechanism. Inclusion criteria were satisfied by 39 studies. In vivo consumption of A1 relative to A2 delays intestinal transit in rodents via an opioid-mediated mechanism. Rodent models also link consumption of A1 to the initiation of inflammatory response markers plus enhanced Toll-like receptor expression relative to both A2 and nonmilk controls. Although most rodent responses are confirmed as opioid-mediated, there is evidence that dipeptidyl peptidase 4 stimulation in the jejunum of rodents is via a nonopioid mechanism. In humans, there is evidence from a limited number of studies that A1 consumption is also associated with delayed intestinal transit (1 clinical study) and looser stool consistency (2 clinical studies). In addition, digestive discomfort is correlated with inflammatory markers in humans for A1 but not A2. Further research is required in humans to investigate the digestive function effects of A1 relative to A2 in different populations and dietary settings.
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