Selectivity of d[Cha4]AVP and SSR149415 at human vasopressin and oxytocin receptors:: evidence that SSR149415 is a mixed vasopressin V1b/oxytocin receptor antagonist

1 A possible role of arginine vasopressin (AVP) V-1b receptor subtype in stress-related disorders has been recently highlighted by the discovery of the agonist [1-deamino-4-cyclohexylalanine] AVP (d[Cha(4)]AVP) and the antagonist SSR149415. Both compounds have been proposed to target specifically V-1b receptors, since the reported affinities for the related V-1a, V-2 and oxytocin receptors are in the micromolar or submicromolar range. In the present study, we further investigated the binding affinities of d[Cha(4)]AVP and SSR149415 at recombinant human vasopressin V-1b (hV(1b)) and oxytocin (hOT) receptors expressed in Chinese hamster ovary (CHO) cells and functional properties of both compounds at hV(1b), hV(1a), hV(2) and hOT receptors. 2 d[Cha4] AVP bound to hV(1b) receptors and hOT receptors with pK(i) values of 9.68 +/- 0.06 and 7.68 +/- 0.09, respectively. SSR149415 showed pK(i) values of 9.34 +/- 0.06 at hV(1b) and 8.82 +/- 0.16 at hOT receptors. 3 d[Cha(4)]AVP stimulated [Ca2+](i) increase in hV(1b)-CHO cells with a pEC(50) value of 10.05 +/- 0.15. It showed pEC(50) values of 6.53 +/- 0.17 and 5.92 +/- 0.02 at hV(1a) and hV(2) receptors, respectively, and behaved as a weak antagonist at hOT receptors (pK(B) 6.31 +/- 0.12). SSR149415 inhibited the agonist-nduced [Ca2+](i) increase with pK(B) values of 9.19 +/- 0.07 in hV(1b)-CHO and 8.72 +/- 0.15 in hOT-CHO cells. A functional pKi value of 7.23 +/- 0.10 was found for SSR1494151 at hV(1a) receptors, whereas it did not inhibit 20 nM AVP response at hV(2) receptors up to 3 mu M. 4 Data obtained confirmed the high potency and selectivity of d[Cha(4)] AVP at hV(1b) receptors, but revealed that SSR149415, in addition to the high potency at hV(1b) receptors, displays a significant antagonism at hOT receptors.