Gonadal hormones modulate the responsiveness to local beta-blocker-induced antinociception in the temporomandibular joint of male and female rats

BackgroundWe have previously demonstrated that blockade of -adrenoreceptors (-AR) located in the temporomandibular joint (TMJ) of rats suppresses formalin-induced TMJ nociceptive behaviour in both male and female rats, but female rats are more responsive. In this study, we investigated whether gonadal hormones modulate the responsiveness to local -blocker-induced antinociception in the TMJ of rats. MethodsCo-administration of each of the selective (1) (atenolol), (2) (ICI 118.551) and (3) (SR59230A)-AR antagonists with equi-nociceptive concentrations of formalin in the TMJ of intact, gonadectomized and hormone-treated gonadectomized male and female rats. ResultsAtenolol, ICI 118.551 and SR59230A significantly reduced formalin-induced TMJ nociception in a dose response fashion in all groups tested. However, a lower dose of each -AR antagonist was sufficient to significantly reduce nociceptive responses in gonadectomized but not in intact and testosterone-treated gonadectomized male rats. In the female groups, a lower dose of (1)-AR antagonist was sufficient to significantly reduce nociceptive responses in gonadectomized but not in intact or gonadectomized rats treated with progesterone or a high dose of oestradiol; a lower dose of (2)-AR antagonist was sufficient to significantly reduce nociceptive responses in gonadectomized but not in intact and gonadectomized rats treated with low or high dose of oestradiol. ConclusionGonadal hormones may reduce the responsiveness to local -blocker-induced antinociception in the TMJ of male and female rats. However, their effect depends upon their plasma level, the subtype of -AR and the dose of -blockers used. (AU)