Involvement of alpha- and beta-adrenoceptors in antinociception at the lumber spinal level in mice.

To study the role of the adrenergic receptors in the regulation of nociceptive transmission in male albino mice, the antinociceptive activity of adrenergic drugs was tested with a tail-flick method. Subarachnoid infusion of phenylephrine and clonidine into T13-L1 of spinal cord produced a dose-dependent elevation of the nociceptive threshold in sodium pentobarbital anesthetized mice. The inhibitory effect of alpha-adrenoceptor agonists was antagonized by pretreatment with alpha-adrenoceptor antagonists. Isoproterenol also increased the nociceptive threshold significantly. The antinociceptive effect of isoproterenol was reversed by pretreatment with beta antagonist, propranolol. These findings suggest that spinal adrenergic receptors of both alpha and beta types probably are involved in the inhibition of nociceptive transmission.