Failure of presynaptic purinoceptors to modulate noradrenaline release from sympathetic nerves in human dental pulp

The effects of putative presynaptic P1- and/or P2-purinoceptors on the release of noradrenaline from sympathetic nerves in human dental pulp were examined by testing the effects of agonists and an antagonist of these receptors on the stimulation-induced overflow of [3H]noradrenaline from tissue treated with desipramine (0.3 μmol/l) and preincubated with [3H]noradrenaline (0.6 μmol/l). The P1-purinoceptor agonists adenosine (1.0 mmol/l) and 2-chloroadenosine (0.01–1.0 mmol/l) and the antagonist 8-cyclopentyl-1,3-dipropyl xanthine (1.0 μmol/l), and the P2-purinoceptor agonists ATP (0.1 mmol/l) and β,γ-methylene-ATP (0.01 mmol/l), did not modulate the release of noradrenaline. Adenosine was also without effect in dental pulp treated with the α2-adrenoceptor antagonist rauwolscine. It is concluded that presynaptic P1-purinoceptors and those P2-purinoceptors activated by adenine nucleotides are either not present on sympathetic nerves in human dental pulp or that they exert little or no effect on the release of noradrenaline.