V,-Type Vasopressin Receptors in Rat Brain Septum: Binding Characteristics and Effects on lnositol Phospholipid Metabolism

Specific binding sites for3H-arginineQasopressin (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 f 0.3 nM and total binding capacity of 22.6 k 4.2 fmol/mg protein. Binding displacement studies with peptide analogs of AVP indicate that this binding site is similar to the V, (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-l -phosphate (IP,) in the presence of 7 mu lithium. This effect was dose dependent with maximal stimulation (65% over basal) occurring at a concentration of 0.5 PM AVP. Higher concentrations, however, tended to inhibit phosphoinositide hydrolysis. The vasopressin-stimulated accumulation of 3H-IP, was completely inhibited by the vasopressin V, antagonist, d(CH,),[Tyr(Me)2]AVP, in a concentration-dependent manner. Oxytocin, at concentrations of 1O-8 and 1O-5 M, only slightly increased 3H-IP, accumulation (17-20% over basal). In contrast, the V, agonist deamino-D-arginine vasopressin (dDAVP), failed to produce significant stimulation of 3H-IP, 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 V,-type vasopressin receptors.