Adrenoceptors in the cat choledochoduodenal junction studied in situ.

1. The effects of adrenaline, noradrenaline, isoprenaline and terbutaline (PINN), 1-(3,5-dihydroxyphenyl)-2(t-butylamino)-ethanol, on the sphincter of Oddi were studied in anaesthetized cats. Both adrenaline and noradrenaline (1-4 mug/kg) increased resistance to flow through the sphincter. This effect was blocked by dibenamine (0.5-2.5 mg/kg) and by phenoxybenzamine (0.5-1.0 mg/kg).2. Isoprenaline (0.5-5.0 mug/kg) as well as terbutaline (0.5-10.0 mug/kg) inhibited the spontaneous sphincter activity and decreased flow resistance. In these doses, isoprenaline provoked marked tachycardia and relaxation of the duodenum, whereas the cardial and intestinal effects of terbutaline were minimal. The effects were blocked by propranolol (0.5-1.0 mg/kg).3. The results confirm earlier observations of the presence of alpha-adrenoceptors active in contraction of the sphincter musculature and of beta-adrenoceptors active in its relaxation. It is suggested that the beta-adrenoceptors belong to the beta(2) type according to Lands' classification.