Novel molecular mechanisms in the inhibition of adrenal aldosterone synthesis: Action of tolvaptan via vasopressin V2 receptor-independent pathway.

<bold>Background and Purpose: </bold>We investigated the inhibitory effect and associated molecular mechanisms of tolvaptan on angiotensin II (AngII)-induced aldosterone production in vitro and in vivo.<bold>Experimental Approach: </bold>In vitro, H295R human adrenocarcinoma cells were incubated with 1 μmol·L-1 arginine vasopressin (AVP) or dDAVP, or tolvaptan (0.1, 1, and 3 μmol·L-1 ) in the presence and absence of 100 nmol·L-1 of AngII. In vivo, Sprague-Dawley rats were treated with tolvaptan 0.05% in the diet for 6 days in the presence and absence of 200 pmol·min-1 AngII.<bold>Key Results: </bold>Tolvaptan suppressed AngII-induced aldosterone production in a dose-dependent manner in H295R cells, whereas neither AVP nor dDAVP in the presence or absence of AngII altered aldosterone production, suggesting the vasopressin V2 receptor was not involved in the inhibitory effect of tolvaptan on aldosterone synthesis. In addition, tolvaptan inhibited the AngII-induced increase in aldosterone synthase (CYP11B2) protein levels without suppressing CYP11B2 mRNA expression. Notably, tolvaptan increased the levels of unfolded protein response (UPR) marker DDIT3 and eIF2α phosphorylation (a UPR-induced event), which could block the translation of CYP11B2 mRNA into protein and thereby inhibit aldosterone production. In vivo, tolvaptan significantly inhibited AngII-induced increases in serum and adrenal aldosterone levels and CYP11B2 protein levels. This anti-aldosterone effect was associated with a reduction in the elevated systolic and diastolic BP.<bold>Conclusions and Implications: </bold>Tolvaptan inhibited AngII-stimulated aldosterone production via a V2 receptor-independent pathway, which can counteract or even surpass its potential activating effect of diuresis-induced aldosterone secretion in certain aldosterone-mediated pathological conditions. [ABSTRACT FROM AUTHOR]