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]nora drenaline (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]noradrena line, 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 adr enaline (0.001 and 0.01 mu mol/l) in the presence of DMI and DMI plus rauwo lscine. Although presynaptic inhibitory alpha(2)- and facilitatory beta-adr enoceptors are present on sympathetic nerves in human dental pulp, these re sults imply that adrenaline activates only the inhibitory alpha(2)-receptor s. (C) 1999 Elsevier Science Ltd. All rights reserved.