Adrenoceptors of the chick rectum

1. The aim of the investigation was to determine whether the adrenoceptors of the chick rectum preparation complied with Ahlquist's classification; phentolamine (0.1 mug/ml) and propranolol (0.05 mug/ml) were used as specific antagonists of alpha- and beta-adrenoceptors, respectively.2. Propranolol antagonized phenylephrine, isoprenaline and noradrenaline in the chick rectum preparation, although according to Ahlquist's classification phenylephrine stimulates alpha-adrenoceptors selectively.3. In the presence of propranolol, phenylephrine and noradrenaline produced small residual relaxations of the chick rectum preparation which were blocked by phentolamine. In the absence of propranolol, however, phentolamine did not antagonize relaxations to phenylephrine, isoprenaline or noradrenaline.4. The adrenoceptors of the guinea-pig colon preparation compiled with Ahlquist's classification in that they were like those generally present in intestine.