Abstract
Effects of C-terminal octapeptide of cholecystokinin (C8-CCK) and prostaglandins E1, E2 and F2α on noradrenaline-induced responses and 3H-noradrenaline release in the gallbladder and sphincter of Oddi of guinea pigs were examined. In the sphincter of Oddi, noradrenaline in low concentrations induced a relaxation which was blocked by either phentolamine or propranolol, while noradrenaline in high concentrations induced a contraction which was blocked by phentolamine. These results suggest the existence of excitatory and inhibitory α-receptors and inhibitory β-receptors in the sphincter of Oddi. In the gallbladder, the adrenergic receptors are α-excitatory and β-inhibitory. C8-CCK (10-9 g/ml) potentiated both contractile and relaxing responses to noradrenaline, in the gallbladder. The same concentration of prostaglandins potentiated only contractile response to noradrenaline. In the sphincter of Oddi, noradrenaline-induced responses were not affected by C8-CCK and prostaglandins. Prostaglandins inhibited 3H-efflux evoked by electrical stimulation, while C8-CCK had no effect on the 3H-efflux from both preparations. These results suggest that C8-CCK enhances the contractile and relaxing responses to noradrenaline, and that prostaglandins act in a similar way on the postsynaptic response and, in addition, inhibit presynaptically the release of noradrenaline in the gallbladder. In the sphincter of Oddi, only prostaglandins inhibit the presynaptic event.
