Effects of C-terminal octapeptide of cholecystokinin and prostaglandins on adrenergic functions in the guinea-pig gallbladder and sphincter of Oddi.

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Abstract
Effects of C-terminal octapeptide of cholecystokinin (C5-CCK) and prostaglandins [PG] E1, E2 and F2.alpha. on noradrenaline[norepinephrine, NA]-induced responses and 3H-NA release in the gallbladder and sphincter of Oddi of guinea pigs were examined. In the sphincter of Oddi, NA in low concentrations induced a relaxation which was blocked by phentolamine or propranolol, while NA in high concentrations induced a contraction which was blocked by phentolamine. Excitatory and inhibitory .alpha.-receptors and inhibitory .beta.-receptors exist in the sphincter of Oddi. In the gallbladder, the adrenergic receptors are .alpha.-excitatory and .beta.-inhibitory. C8-CCK (10-9 g/ml) potentiated both contractile and relaxing responses to NA, in the gallbladder. The same concentration of PG potentiated only contractile response to NA. In the sphincter of Oddi NA-induced responses were not affected by C8-CCK and PG PG inhibited 3H-efflux evoked by electrical stimulation, while C8-CCK had no effect on the 3H-efflux from both preparations. C8-CCK enhances the contractile and relaxing responses to NA and PG act in a similar way on the postsynaptic response and inhibit presynaptically the release of NA in the gallbladder. In the sphincter of Oddi, only PG inhibit the presynaptic event.