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 [H-3]noradrenaline from tissue treated with desipramine (0.3 mu mol/l) and preincubated with [H-3]noradrenaline (0.6 mu mol/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 mu mol/l), and the P2-purinoceptor agonists ATP (0.1 mmol/l) and beta,gamma-methylene-ATP (0.01 mmol/l), did not modulate the release of noradrenaline. Adenosine was also without effect in dental pulp treated with the alpha(2)-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. (C) 2000 Elsevier Science Ltd. All rights reserved.