Novel molecular mechanisms in the inhibition of adrenal aldosterone synthesis: Action of tolvaptan via vasopressin V 2 receptor-independent pathway

Abstract

Background and Purpose: We investigated the inhibitory effect and associated molecular mechanisms of tolvaptan on angiotensin II (AngII)-induced aldosterone production in vitro and in vivo. Experimental Approach: 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. Key Results: 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 V 2 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. Conclusions and Implications: Tolvaptan inhibited AngII-stimulated aldosterone production via a V 2 receptor-independent pathway, which can counteract or even surpass its potential activating effect of diuresis-induced aldosterone secretion in certain aldosterone-mediated pathological conditions.