Journal of Neuroscience, Vol 8, 1671-1677, Copyright © 1988 by Society for Neuroscience
V1-type vasopressin receptors in rat brain septum: binding characteristics and effects on inositol phospholipid metabolism
LM Shewey and DM Dorsa
Geriatric Research, Education and Clinical Center, Veterans Administration Medical Center, Seattle, Washington 98108.
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 microM 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.