Method: Each of the β1 (2, 6, 18, 54µg) and β2 (0.1, 0.3, 0.9µg) adrenoceptor antagonist, Atenolol and ICI 118.551, respectively, was co-administrated with 0.9% NaCl or equinociceptive concentrations of Formalin (1.0 or 1.5%) into the TMJ of ovariectomized female Wistar rats (200-300g) treated with progesterone, with a high dose (30 μg/day) or with a low dose (3 μg/day) of estrogen, or with their vehicle. The nociceptive behavior was quantified for 45 minutes and used as a quantitative nociceptive behavior measure. The data were analyzed by One Way ANOVA and Tukey post-hoc test (p<0.05). Number of rats was 6 per group.
Result: Atenolol and ICI 118.551 significantly reduced formalin-induced TMJ nociception in a dose response fashion in all females. However, a lower dose of ICI 118.551 was sufficient to significantly reduce formalin-induced TMJ nociception in ovariectomized females treated with a low dose of estrogen or with its vehicle than in ovariectomized females treated with progesterone or with a higher dose of estrogen. Administration of the highest doses of each β-adrenoceptor antagonist in the TMJ contralateral to that receiving formalin did not affect formalin-induced nociception in all females, confirming the local action of the β-adrenoceptor antagonists.
Conclusion: The findings of this study indicate that estrogen and progesterone modulate the antinociception induced by β2 but not β1 adrenoceptor blockers by reducing its antinociceptive effect in the TMJ of females.