Adrenoceptor Functions in the Cat Choledochoduodenal Junction in Vitro

1. The effects of alpha- and beta-adrenoceptor stimulating agents were investigated on three different kinds of preparation of the isolated sphincter of Oddi and on the duodenum of the cat.2. Adrenaline (1.5 x 10(-7)M-6.3 x 10(-7)M), noradrenaline (1.6 x 10(-7)M-6.3 x 10(-7)M), and tyramine (2.9 x 10(-6)M-5.8 x 10(-6)M) increased the activity and tonus of the sphincter musculature and decreased duodenal activity and tone. The effect on the sphincter resulted in increased resistance to flow through the sphincter. The excitatory effects on the sphincter were blocked by phenoxybenzamine (1.7 x 10(-8)M-1.7 x 10(-7)M).3. No effect was produced by tyramine in concentrations up to 4.6 x 10(-5)M on sphincters taken from reserpinized cats. It is suggested that the cat sphincter of Oddi contains adrenergic nerves of functional importance.4. Isoprenaline (1.9 x 10(-8)M-4.7 x 10(-7)M) and terbutaline (3.5 x 10(-7)M-8.8 x 10(-6)M) decreased spontaneous activity and tonus of the sphincter, and diminished resistance to flow through the sphincter. Both agents decreased spontaneous activity and tonus of the duodenum. On a molar basis, isoprenaline was 2-18 times more active than terbutaline on the sphincter and 35-90 times more active on the duodenum. The effects of isoprenaline and terbutaline were blocked by propranolol (3.9 x 10(-7)M).5. It is concluded that the cat sphincter of Oddi contains alpha-adrenoceptors active in contraction of the sphincter, and beta-adrenoceptors active in its relaxation. The beta-adrenoceptors of the sphincter differ from those in the duodenum; it is suggested that they belong to the beta(2)-group (according to Lands' classification).6. The automaticity of the isolated sphincter of Oddi resembled the sphincter activity recorded in vivo and is probably myogenic in nature, as it resisted treatment with phenoxybenzamine (1.7 x 10(-8)M-1.7 x 10(-7)M), atropine (1.4 x 10(-6)M-5.8 x 10(-6)M), hexamethonium (1.4 x 10(-5)M-1.1 x 10(-4)M) and tetrodotoxin (1 mug/ml). The activity of the sphincter has no propulsive function but prevents passage of fluid through the sphincter.