Spinal zaprinast, phospodiesterase inhibitor, has been shown to have an antinociception through an increase of cGMP. The aim of this study was to examine the role of spinal adrenergic and cholinergic receptors on the antinociceptive action of intrathecal zaprinast.

Rats were implanted with lumbar intrathecal catheters. After formalin injection, formalin-induced nociceptive behavior (flinching response) was observed for 60 min. After observing the effect of intrathecal zaprinast, antagonism of intrathecal prazosin, yohimbine, atropine and mecamylamine for the effect of zaprinast were evaluated.

Intrathecal zaprinast produced a dose-dependent suppression of formalin-induced flinches in both phases of the formalin test. Intrathecal prazosin reversed the antinociception of zaprinast in phase 2, but not phase 1. Intrathecal yohimbine reversed the antinociception of zaprinast in both phases. Neither atropine nor mecamylamine reversed the antinocicetive action of zaprinast.

Intrathecal zaprinast is against the nociceptive state evoked by formalin stimulus. Alpha 2 or alpha 1 adrenergic receptor, but not cholinergic receptors, may be related to the action of zaprinast in the spinal cord.