Opioid modulation of oxytocin release from spinal cord synaptosomes

Regulation of oxytocin release from spinal cord synaptosomes was investigated using in vitro preparations. Experiments were designed to determine whether opioid peptides regulate oxytocin release from spinal cord synaptosomes, as they do from synaptosomes derived from neurohypophysis. Oxytocin release was evoked by the addition of 56 mM KCl in synaptosomes prepared from thoracic and lumbosacral parts of the spinal cord. Addition of 5 microM naloxone, 1 min prior to the addition of the stimulus, caused a significant (p < 0.025) increase of oxytocin release. Prior addition of 5 microM dynorphin, demonstrated a significant (p < 0.01) decrease whereas addition of 5 microM [D-Ala2,N-Me-Phe4,Gly-ol]-enkephalin showed no effect on KCl-induced OT release. The results suggest that spinal cord OT release is under inhibitory control of opioid peptides and the opioids act via the kappa opioid receptor.