Santa Cruz Bio Tech no longer sell their polyclonals, and i can only seem to find anti-AVP1AR's with human reactivity, or with no published IHC/IF work, only WB/ELISA.
We list a few sources for anti-AVP1AR that are supposedly reactive with rat and suitable for IHC. See some of our listings here: https://www.linscottsdirectory.com/antibodies?q=vasopressin%20V1a
Filter for rat reactivity and IHC application; follow "more info" to suppliers' pages. Hope this helps.