EFFECT OF BACITRACIN ON THE DEGRADATION OF A VASOPRESSIN RECEPTOR-LIGAND WITH HIGH-AFFINITY FOR THE V-1 AND V-2 VASOPRESSIN ISORECEPTORS

We previously described a new iodinated vasopressin analogue (N-epsilon-[I-125]L-Tyr-[Lys(8)]-vasopressin) with high affinity for the vasopressin V-1 and V-2 isoreceptors. The aim of the present study was: i) to analyse the degradation pathway of N-epsilon-[I-125]L-Tyr-[Lys(8)]-vasopressin and ii) to look for an effective inhibitor of radioligand degradation. N-epsilon-[I-125]L-Tyr-[Lys(8)]-vasopressin was processed in a temperature-dependent manner by crude cell membranes from LLC-PK1 cells. Only one degradation product was seen using RP-HPLC. The degradation product co-eluted with monoiodotyrosine. The stereoisomer, N-epsilon-[I-125]D-Tyr-[Lys(8)]-vasopressin, underwent the same degradation process. Bacitracin prevented degradation at doses as low as 40 mg/l without alterating the binding affinity.