Modulation by presynaptic beta-adrenoceptors of noradrenaline release fromsympathetic nerves in human dental pulp

This study was undertaken to test for the presence of presynaptic beta-adre noceptors on sympathetic nerves in human dental pulp and, if present, to in vestigate the subtype. Pulp was excised from freshly extracted teeth, incub ated with [H-3]-noradrenaline (0.6 mu mol/l) and subsequently superfused wi th Krebs solution. Sympathetic nerves were stimulated at 5 Hz for 100 sec. The non-specific beta-adrenoceptor agonist isoprenaline (1.0 mu mol/l), and the selective beta(2)-agonist salbutamol (10 mu mol/l) facilitated the rel ease of [H-3]-noradrenaline; isoprenaline, but not salbutamol, also facilit ated this release in the presence of desipramine (DMI, 0.3 mu mol/l), corti costerone (10 mu mol/l) and rauwolscine (0.1 mu mol/l). BRL 37344 (1.0 mu m ol/l), a beta(3)-agonist, had no effect on [H-3]-noradrenaline release. The facilitatory effects of isoprenaline and salbutamol were inhibited by the non-specific beta-antagonist propranolol (10 mu mol/l), while that of salbu tamol was inhibited in the presence of ICI-188,551 (10 mu mol/l), a selecti ve beta(2)-antagonist, as well. The beta(1)-antagonist atenolol (1.0 mu mol /l) potentiated the facilitatory effects of isoprenaline in the presence of DMI and corticosterone. Neither propranolol nor ICI-188,551 alone affected the release of [H-3]-noradrenaline. These results establish the presence o f presynaptic beta-adrenoceptors on sympathetic nerves in human dental pulp . It is suggested that they are of the beta(2)-subtype, although a greater range of agonists and antagonists needs to be used to clarify the nature of the beta-adrenoceptors. (C) 1998 Elsevier Science Ltd. All rights reserved .