The purpose of this study was to examine the effect of peptide YY on contraction of the gallbladder in vivo and in vitro and on contraction of the sphincter of Oddi in vitro. In conscious dogs that were prepared with strain-gauge force transducers implanted in the gallbladder wall, peptide YY (400 ng/kg, bolus; 800 pmol/kg · h, infusion) did not affect the resting contractile pattern of the gallbladder, nor did it inhibit cholecystokinin-octapeptide (CCK-8)-stimulated gallbladder contraction. In contrast, the cholecystokinin antagonist proglumide (5, 10, 20, 40, or 80 mg/kg), given in vivo, inhibited CCK-8-stimulated gallbladder contraction in a dose-related manner. The highest dose of proglumide (80 mg/kg) completely abolished contraction of the gallbladder stimulated by CCK-8. In vitro studies showed that peptide YY (0.25, 0.5, or 1 μg/ml) did not affect the resting tension of rabbit gallbladder strips, and it did not inhibit CCK-8-stimulated contraction of gallbladder strips. Proglumide (0.4, 0.8, 1.6, or 3.2 mg/ml) inhibited CCK-8-stimulated tension of gallbladder strips in a dose-related manner. Peptide YY and CCK-8 had no effect on the motility of the canine sphincter of Oddi in vitro, whereas acetylcholine caused contraction and adrenergic agonists caused relaxation. These results suggest that peptide YY and pancreatone (a peptidelike substance, extracted from ileal and colonic mucosa, that inhibits CCK-8-stimulated gallbladder contraction in vivo) do not appear to be identical.
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