Interplay between nitric oxide and VIP in CCK-8-induced phasic contractile activity in the rabbit sphincter of Oddi

AIM: The sphincter of Oddi (SO) plays an important role in delivery of bile into the duodenum. To establish whether vasoactive intestinal polypeptide (VIP) and nitric oxide (NO) were involved in phasic contractile activity of the rabbit SO stimulated by cholecystokinin-octapeptide (CCK-8).METHODS: Isolated SO muscle rings were cleaned of fat and mounted horizontally on two small L-shaped hooksone of which was connected to a force transducer for the measurement of isometric tension. The experiments were carried out in a thermostatically controlled (37±0.2℃)organ bath (5 mL) containing Krebs solution. The organ fluid was gassed with 95% O2 and 50 mL/L CO2 to keep the pH at 7.40±0.05. Contractile responses to CCK-8 (1μmol/L) were evaluated in the presence and absence of N^G-nitro-L-arginine (LNNA), an inhibitor of NO synthase (100μmol/L), and (p-chloro-D-Phe^6-Leu^17)-VIP (VIPa,30μmol/L), a VIP receptor antagonist.RESULTS: CCK-8 stimulated the phasic activity of the SO.NO synthase inhibition increased the frequency and amplitude of contractions with a slight increase in developed tension.Pre-incubation with VIPa also attenuated this CCK-8 effect.The combined application of LNNA and VIPa abolished the phasic activity of the muscle rings with a marked increase in tension in response to CCK-8.CONCLUSION: VIP and NO together contribute to an increase in phasic activity of SO.

Ethanol inhibits the motility of rabbit sphincter of Oddi in vitro

AIM: The role of the sphincter of Oddi (SO) in ethanol (ETOH)-induced pancreatitis is controversial. Our aim was to characterise the effect of ETOH on basal and stimulated SO motility.METHODS: SOs removed from white rabbits were placed in an organ bath (Krebs solution, pH7.4, 37℃). The effects of 2 mL/L, 4 mL/L, 6 mL/L and 8 mL/L of ETOH on the contractile responses of the sphincter were determined.1 SOs were stimulated with either 0.1μol/L carbachol, 1μol/L erythromycin or 0.1μol/L cholecystokinin (CCK).RESULTS: ETOH at a dose of 4 mL/L significantly decreased the baseline contractile amplitude from 11.98±0.05 mN to 11.19±0.07 mN. However, no significant changes in the contractile frequency were observed. ETOH (0.6%) significantly decreased both the baseline amplitude and the frequency compared to the control group (10.50±0.01 mN,12.13±0.10 mN and 3.53±0.13 c/min, 5.5±0.13 cycles(c)/min,respectively). Moreover, 0.8% of ETOH resulted in complete relaxation of the SO. Carbachol (0.1μol/L)or erythromycin (1μol/L) stimulated the baseline amplitudes (by 82% and 75%, respectively) and the contractile frequencies (by 150% and 106%, respectively). In the carbachol or en/thromydn-stimulated groups 2-6 mL/L of ETOH significantly inhibited both the amplitude and the frequency. Interestingly,a 4-5 min administration of 6 mL/L ETOH suddenly and completely relaxed the SO. CCK (0.1μol/L) stimulated the baseline amplitude from 12.37±0.05 mN to 27.40±1.82 mN within 1.60±0.24 min. After this peak, the amplitudede creased to 17.17±0.22 mN and remained constant during the experiment. The frequency peaked at 12.8±0.2 c/min,after which the constant frequency was 9.43±0.24 c/min throughout the rest of the experiment. ETOH at a dose of 4 mL/L significantly decreased the amplitude from 16.13±0.23 mN to 14.93±0.19 mN. However, no significant changes in the contractile frequency were observed. ETOH at a dose of 6 mL/L inhibited both the amplitudes and the frequencies in the CCK-stimulated group, while 8 mL/L of ETOH completely relaxed the SO.CONCLUSION: ETOH strongly inhibits the basal, carbachol,erythromycin, and CCK-stimulated rabbit SO motility.Therefore, it is possible that during alcohol-intake the relaxed SO opens the way for pancreatic fluid to flow out into the duodenum in rabbits. This relaxation of the SO may protect the pancreas against alcohol-induced damage.