The ability of d(CH2)5‐Tyr(Me)‐arginine‐8‐vasopressin, an antagonist of peripheral pressoric (V1‐type) vasopressin receptors, to label vasopressin binding sites in the septum of the rat brain was evaluated. Using crude membrane preparations from the septum, 3H‐arginine‐8‐vasopressin (AVP) specifically labels a single class of binding sites with a Kd of 2.9nM and maximum binding site concentration of 19.8 fmole/mg protein. 3H‐Antag also labels a single class of membrane sites but with higher affinity (Kd=0.47nM) and lower capacity (10.1 fmole/mg protein) than 3H‐AVP. The rank order of potency of various competitor peptides for 3H‐AVP and 3H‐Antag binding was similar. Oxytocin was 100–1,000 fold less potent than AVP in competing for binding with both ligands. 3H‐AVP and 3H‐Antag showed similar labeling patterns when incubated with septal tissue slices. Unlabeled Antag also effectively antagonized vasopressin‐stimulated phosphatidylinositol hydrolysis in septal tissue slices.
- Phosphoinositide metabolism
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience