V₁-type vasopressin receptors in rat brain septum: Binding characteristics and effects on inositol phospholipid metabolism

Specific binding sites for ³H-arginine⁸-vasopressin (AVP) have been characterized in rat septal membranes. Scatchard analyses revealed a single class of high-affinity binding sites having an equilibrium dissociation constant of 1.7 ± 0.3 nM and total binding capacity of 22.6 ± 4.2 fmol/mg protein. Binding displacement studies with peptide analogs of AVP indicate that this binding site is similar to the V₁ (pressor)-type receptor for AVP. When added to rat brain septal slices that had been prelabeled with ³H-myo-inositol, vasopressin stimulated the accumulation of ³H-inositol-1-phosphate (IP₁) in the presence of 7 mM lithium. This effect was dose dependent with maximal stimulation (65% over basal) occurring at a concentration of 0.5 μM AVP. Higher concentrations, however, tended to inhibit phosphoinositide hydrolysis. The vasopressin-stimulated accumulation of ³H-IP₁ was completely inhibited by the vasopressin V₁ antagonist, d(CH₂)₅[Tyr(Me)²]AVP, in a concentration-dependent manner. Oxytocin, at concentrations of 10^-8 and 10^-5 M, only slightly increased ³H-IP₁ accumulation (17-20% over basal). In contrast, the V₂ agonist deamino-D-arginine vasopressin (dDAVP), failed to produce significant stimulation of ³H-IP₁ accumulation, even at high concentrations. The effects of these analogs on phosphoinositide hydrolysis is consistent with their potencies in displacing ³H-AVP from septal binding sites. These results indicate that vasopressin stimulates hydrolysis of inositol phospholipids in rat brain septum through an interaction with V₁-type vasopressin receptors.