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 [H-3]noradrenaline (0.6 mu mol/l). In the presence of desipramine (DMI, 0.3 mu mol/l), adrenaline (0.1 and 1.0 mu mol/l) inhibited the release of [3H]noradrenaline, an effect which was inhibited by the alpha(2)-adrenoceptor antagonist rauwolscine (0.1 mu mol/l) and by the alpha(2)-adrenoceptor agonist UK 14,304 (0.1 mu mol/l). The release of [H-3]noradrenaline was unaffected by adrenaline (0.001 and 0.01 mu mol/l) in the presence of DMI and DMI plus rauwolscine. Although presynaptic inhibitory alpha(2)- and facilitatory beta-adrenoceptors are present on sympathetic nerves in human dental pulp, these results imply that adrenaline activates only the inhibitory alpha(2)-receptors. (C) 1999 Elsevier Science Ltd. All rights reserved.