**Marco Simonini, Paola Casanova, Lorena Citterio, Elisabetta Messaggio, Chiara Lanzani and Paolo Manunta \***

Genomics of Renal Disease and Hypertension Unit, IRCCS San Raffaele Scientific Institute, Università Vita Salute San Raffaele, 20132 Milan, Italy; simonini.marco@hsr.it (M.S.); casanova.paola@hsr.it (P.C.); citterio.lorena@hsr.it (L.C.); messaggio.elisabetta@hsr.it (E.M.); lanzani.chiara@hsr.it (C.L.)

**\*** Correspondence: manunta.paolo@hsr.it; Tel.: +39-02-2643-3890 (ext. 5330)

Received: 22 May 2018; Accepted: 29 June 2018; Published: 3 July 2018

**Abstract:** The endogenous ouabain (EO) is a steroid hormone secreted by the adrenal gland with cardio-tonic effects. In this article, we have reviewed and summarized the most recent reports about EO, particularly with regard to how it may interact with specific genetic backgrounds. We have focused our attention on the EO's potential pathogenic role in several diseases, including renal failure, essential hypertension and heart failure. Notably, these reports have demonstrated that EO acts as a pro-hypertrophic and growth-promoting hormone, which might lead to a cardiac remodeling affecting cardiovascular functions and structures. In addition, a possible role of EO in the development of acute kidney injury has been hypothesized. During the last decays, many important improvements permitted a deeper understanding of EO's metabolisms and functions, including the characteristics of its receptor and the effects of its activation. Such progresses indicated that EO has significant implications in the pathogenesis of many common diseases. The patho-physiological role of EO in the development of hypertension and other cardiac and renal complications have laid the basis for the development of a new selective compound that could selectively modulate the genetic and molecular mechanisms involved in EO's action. It is evident that the knowledge of EO has incredibly increased; however, many important areas remain to be further investigated.

**Keywords:** cardio-tonic steroids; endogenous ouabain; adducin; hypertension; renal damage
