Permissive, Mediating and Potentiating Effects of Vasopressin in the ACTH and β-Endorphin Response to Histamine and Restraint Stress

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Abstract
We investigated in conscious, male rats (1) whether the role of arginine-vasopressin (AVP) in histamine (HA)- and/or restraint stress-induced stimulation of ACTH and β-endorphin (β-END) secretion is mediating and/or permissive and (2) whether AVP possesses a potentiating effect on HA- or stress-induced release of ACTH and β-END. Administration of a specific V1 receptor agonist stimulated ACTH and β-END secretion dose-dependently while a V2 receptor agonist had no stimulating effect. ACTH and β-END secretion was stimulated 2- to 3-fold by intracerebroventricular (i.e.v.) infusion of HA (270 nmol) or by 5 min of restraint stress. These effects were inhibited approximately 80% by immunoneutralization of endogenous AVP using a specific AVP antiserum. When the ‘AVP tone’ was restored in immunoneutralized animals by administration of the specific AVP V1 receptor agonist, which was not bound by the AVP antiserum and had no ACTH and β-END-releasing effect in the dose used, the ACTH and β-END response to HA or restraint stress was almost completely reestablished. The specific AVP V2 receptor agonist, which was not bound by the AVP antiserum, reestablished only in part the response of ACTH and β-END to HA or restraint stress in immunoneutralized animals. AVP administered in doses which had no or minimal ACTH or β-END releasing effect in itself enhanced the ACTH or β-END response to submaximal stimulation with HA or restraint stress. We conclude the following. (1) The direct stimulatory effect of AVP on ACTH and β-END secretion in conscious rats is medited via V1 receptors (or similar receptors with affinity for the V1 agonist used). (2) The role of AVP in HA- and stress-induced secretion of ACTH and β-END appears, at least in part, to be permissive. This effect is mediated primarily via V1 receptors whereas V2 receptors play a minor role. In addition to its permissive action AVP may have a mediating effect. (3) AVP seems to potentiate the effect of HA or stress on ACTH and β-END secretion.

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