SPECIAL REPORT Noradrenaline‐induced relaxation of rat oesophageal muscularis mucosae: mediation solely by innervated β3‐adrenoceptors

We investigated the effects of cocaine and corticosterone on the noradrenaline‐induced relaxation of rat oesophageal smooth muscle in the absence and presence of the selective β2‐antagonist, ICI 118,551. It was found that the concentration‐response curve (CRC) of noradrenaline was not shifted by ICI 118,551 at 1 μM, whereas a clear shift to the right was observed at 100 μM of the antagonist. In the presence of corticosterone (10 μm), CRCs were clearly shifted to the left; with cocaine (10 μM) additionally present, a further leftward shift was observed, indicating the involvement of both neuronal and extraneuronal uptake sites. It was concluded that the relaxation of rat oesophageal muscularis mucosae by noradrenaline is solely mediated by β3‐adrenoceptors which are sympathetically innervated.