Effects of administration of α ₂ adrenergic receptor agonist into psoas major muscle on inflammatory pain induced by injection of complete Freund’s adjuvant in rats

Abstract

α ₂ adrenergic agonists are widely used in clinical anesthesia and ICU sedation owing to their effective sedative and analgesic effects. Lumbago and leg pain is the most common clinical pain disease. Studies have reported that lumbago and leg pain is associated with dysregulation of paravertebral muscles, especially psoas major muscles. In the present study, a unilateral lower extremity chronic inflammation and pain model was established by subcutaneous administration of low-dose complete Fredrin’s adjuvant (CFA) into the posterior paw of rats. α ₂ adrenalin receptor agonist was then injected into the psoas major muscle. Behavioral tests were conducted for 21 days. Psoas major muscle tissue was harvested for evaluation of biochemical indexes related to pain. The effect of α ₂ adrenergic receptor agonist injected into psoas major muscle on chronic inflammatory pain of lower extremities in rats was explored. The results showed that injection of α ₂ adrenergic receptor agonist into the psoas major muscle relieved CFA-induced mechanical hyperalgesia. Administration of α ₂ adrenergic receptor antagonist yohimbine reversed the analgesic effect of α ₂ adrenergic receptor agonists. Administration of dexmedetomidine into psoas major muscle downregulated the levels of norepinephrine, interleukin-6 and tumor necrosis factor-α in tissues. The findings of the present study show that administration of α ₂ adrenoceptor agonists into the psoas major muscle relieves chronic inflammatory pain induced by CFA. Local injection of dexmedetomidine also exerted anti-inflammatory and anti-sympathetic effect by activating α ₂-adrenoceptor in the psoas major muscle.