Tetraethylammonium ions and 4-aminopyridine prevent opioid inhibition of neurohypophysial oxytocin release.

Naloxone increased the electrically (15 Hz, 1 min) evoked release of oxytocin from isolated neural lobes of rats 3-4-fold. In the presence of 4-aminopyridine or tetraethylammonium ions the evoked release of oxytocin was increased 8-9-fold and remained unaffected by naloxone. Increasing the calcium concentration in the medium from 1.2 to 3 mM caused only a marginal increase of the evoked oxytocin release. In conclusion, blockade of potassium channels and/or the resulting prolongation of the action potential can surmount the opioid inhibition of oxytocin release.