EXPERIMENTAL STUDY Serotonergic involvement in stress-induced vasopressin and oxytocin secretion

Objective: To investigate the involvement of serotonin (5-hydroxytryptamine – 5-HT) receptors in mediation of stress-induced arginine vasopressin (AVP) and oxytocin (OT) secretion in male rats. Design: Experiments on laboratory rats with control groups. Methods: Different stress paradigms were applied after pretreatment with intracerebroventricular infusion of saline or different 5-HT antagonists. Results: Restraint stress (5 min), hypotensive hemorrhage or dehydration for 24 h increased AVP secretion fivefold and OT secretion threefold. Swim stress for 3 min had no effect on AVP secretion, but increased OT secretion threefold. Ether vapor or hypoglycemia had no effect on AVP or OT secretion. The restraint stress-induced AVP response was inhibited by pretreatment with the 5-HT2Aþ2C antagonists ketanserin (KET) and LY-53857 (LY) and the 5-HT3þ4 antagonist ICS-205930 (ICS), whereas the 5-HT1A antagonist WAY-100635 (WAY) had no effect. The OT response to restraint stress was inhibited by WAY, KET and LY but not by ICS. KET and LY inhibited OT response to dehydration, and LY inhibited OT response to hemorrhage. Neither of the antagonists affected AVP responses to dehydration or hemorrhage, nor the swim stress-induced OT response. Conclusion: 5-HT2A, 5-HT2C and possibly 5-HT3 and 5-HT4 receptors, but not 5-HT1A receptors, are involved in the restraint stress-induced AVP secretion. 5-HT does not seem to be involved in the dehy-dration- or hemorrhage-induced AVP response. The restraint stress-induced OT response seems to be mediated via 5-HT1A, 5-HT2A and 5-HT2C receptors. The dehydration and hemorrhage-induced OT responses are at least mediated by the 5-HT2A and 5-HT2C receptors. The 5-HT3 and 5-HT4 receptors are not involved in stress-induced OT secretion