Inhibitory effects of adrenaline on the release of noradrenaline from sympathetic nerves in human dental pulp

The effects of adrenaline on the release of noradrenaline from sympathetic nerves in human dental pulp in vitro were examined. Sympathetic nerves were stimulated at 5 Hz for 100 sec following incubation of pulp with [3H]noradrenaline (0.6 μmol/l). In the presence of desipramine (DMI, 0.3 μmol/l), adrenaline (0.1 and 1.0 μmol/l) inhibited the release of [3H]noradrenaline, an effect which was inhibited by the α2-adrenoceptor antagonist rauwolscine (0.1 μmol/l) and by the α2-adrenoceptor agonist UK 14,304 (0.1 μmol/l). The release of [3H]noradrenaline was unaffected by adrenaline (0.001 and 0.01 μmol/l) in the presence of DMI and DMI plus rauwolscine. Although presynaptic inhibitory α2- and facilitatory β-adrenoceptors are present on sympathetic nerves in human dental pulp, these results imply that adrenaline activates only the inhibitory α2-receptors.