Intrathecal porcine calcitonin enhances the release of [Met5]enkephalin-like material from the rat spinal cord.

Perfusion of the intrathecal space of halothane-anaesthetized rats with artificial cerebro-spinal fluid supplemented with porcine calcitonin (1-10 microM) produced a significant increase (+67-110%) in the spinal release of [Met5]enkephalin-like material. The effect of porcine calcitonin was markedly enhanced (+100%) in animals receiving a continuous i.v. infusion of the opioid antagonist naloxone (65 micrograms/kg per min). These data strongly suggest that the antinociceptive effect of intrathecal porcine calcitonin might involve a stimulatory action of the hormone on spinal enkephalinergic interneurones. In addition, presynaptic opioid autoreceptors probably control the activity of these neurones in the rat.