Differential involvement of central and peripheral α2 adrenoreceptors in the antinociception induced by aerobic and resistance exercise.

Abstract

Several studies have demonstrated antinociception induced by exercise; however, the specific mechanisms for this effect are not well understood. Thus, we investigated the involvement of α2-adrenergic receptors (α2-ARs) in the antinociceptive effect produced by exercise in rats and mice. Male Wistar rats performed acute aerobic (AA) and acute resistance exercise protocols, and male α2A/α2C-ARs knockout mice and their wild-type mice were also submitted to AA. After the exercise protocols, the nociceptive threshold of rats and wild type was increased, (except in knockout mice). This effect was reversed by yohimbine, a nonselective α2-ARs antagonist (4 mg/kg, subcutaneously [s.c.]); rauwolscine, a selective α2C-ARs antagonist (4 mg/kg, s.c.); BRL 44408, a selective α2A-ARs antagonist (4 mg/kg, s.c.) and guanethidine, a selective inhibitor of transmission in adrenergic nerves (30 mg/kg, intraperitoneal). Furthermore, when given intrathecally or intracerebroventricularly, yohimbine did not alter antinociception induced by exercise protocols. In addition, α2-ARs expression in rat brains did not change after AA and acute resistance exercise. These results suggest a peripheral involvement of α2-ARs in the antinociception induced by aerobic and resistance exercise.