Galanin and galanin-like peptide modulate vasopressin and oxytocin release in vitro: The role of galanin receptors

Galanin (Gal) and galanin-like peptide (GALP) may be involved in the mechanisms of the hypothalamo-neurohypophysial system. The aim of the present in vitro study was to compare the influence of Gal and GALP on vasopressin (AVP) and oxytocin (OT) release from isolated rat neurohypophysis (NH) or hypothalamo-neurohypophysial explants (Hth–NH). The effect of Gal/GALP on AVP/OT secretion was also studied in the presence of galantide, the non-selective galanin receptors antagonist.Gal at concentrations of 10⁻¹⁰ M and 10⁻⁸ M distinctly inhibited basal and K⁺-stimulated AVP release from the NH and Hth–NH explants, whereas Gal exerted a similar action on OT release only during basal incubation. Gal added to the incubation medium in the presence of galantide did not exert any action on the secretion of either neurohormone from NH and Hth–NH explants.GALP (10⁻¹⁰ M and 10⁻⁹ M) induced intensified basal AVP release from the NH and Hth–NH complex as well as the release of potassium-evoked AVP from the Hth–NH. The same effect of GALP has been observed in the presence of galantide. GALP added to basal incubation medium was the reason for stimulated OT release from the NH as well as from the Hth–NH explants. However, under potassium-stimulated conditions, OT release from the NH and Hth–NH complexes has been observed to be distinctly impaired. Galantide did not block this inhibitory effect of GALP on OT secretion.It may be concluded that: (i) Gal as well as GALP modulate AVP and OT release at every level of the hypothalamo-neurohypophysial system; (ii) Gal acts in the rat central nervous system as the inhibitory neuromodulator for AVP and OT release via its galanin receptors; (iii) the stimulatory effect of GALP on AVP and OT release is likely to be mediated via an unidentified specific GALP receptor(s).