[3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP: an AVP V2 receptor antagonist radioligand

Binding characteristics of the selective V2 antagonist radioligand [3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP to rat kidney were determined. Binding was specific, saturable and reversible. The peptide bound to a single class of high-affinity binding sites with Bmax 69.4 +/- 6.8 fmol/mg protein and KD 2.8 +/- 0.3 nM. AVP and other related peptides displaced [3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP binding. The order of potency of inhibition was desamino-D-AVP greater than AVP greater than d(CH2)5[D-Ileu2,Ileu4]AVP greater than oxytocin greater than d(CH2)5[Tyr(Me)2]AVP greater than d(CH2)5[sarcosine7]AVP, which is typical of a selective V2 radioligand. Autoradiographic localization of [3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP binding sites in kidney showed dense binding in the inner and outer medulla with less binding in the cortex, which is consistent with known renal V2 receptor distribution.