Endogenous ET-1 Mediates Hypoxia-induced Atrial ANP Secretion

Objective:Roles of the hypoxia inducible factor-1 alpha (HIF-1alpha) and extracellular signal-regulated kinase (ERK) signaling pathway on the atrial production and release of endothelin-1 (ET-1) are not clear. Therefore, present study is to investigate effect of acute hypoxia on atrial expression of HIF-1alpha and its role on the regulation of ET-1 release in isolated perfused beating rabbit atria. The effect of ERK on govern of ET-1 release in acute hypoxic atria was also to be tested.Methods:Isolated perfused beating rabbit atrial model was used and level of ET-1 was measured by radioimmunoassay. The protein levels of atrial HIF-1alpha and ET-1 receptors were determined by western blot analysis.Results:Acute hypoxia significantly increased levels of atrial HIF-1alpha and phosphorylated ERK (pERK) protein. Hypoxia-induced HIF-1 alpha protein level was abolished not only by its antagonists rotenone (0.5μmol/L) and CAY10585 (10.0 μmol/L), but also by pERK inhibitor PD98059 (30.0μmol/L) respectively. Acute hypoxia also obviously increased atrial ET-1 release and upregulated both of its receptors, ET receptor type A (ETRa) and type B (ETRB), expressions. ERK inhibitor PD98059 dramaticly reversed the hypoxia-induced atrial release of ET-1 and an antagonist of HIF-1alpha rotenone was mimicked role of PD98059 on the regulation of hypoxia-induced of ET-1 release.Conclusion:The findings of the present study indicate that ERK signaling pathway mediates release of ET-1 by controlling HIF-1 alpha protein.Objective:As an important regulator of cardiac function, endothelin-1 (ET-1) is the most potent stimulus for atrial natriuretic peptide (ANP) secretion. However, the mechanism by which endogenous ET-1 regulates hypoxia-induced atrial secretion of ANP is not well known. Therefore, the present study is to investigate the effects of endogenous ET-1 receptors and its downstream mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway on the regulation of hypoxia-induced ANP secretion in isolated perfused beating rabbit atria.Methods:Isolated perfused beating rabbit atrial model was used and levels of ET-1 as well as ANP were measured by radioimmunoassay. The protein levels of atrial ET receptor type A (ETRA), type B (ETRB), phosphorylated ERK (pERK), and the GATA binding protein-4 (GATA-4) were determined by western blot analysis.Results:Acute hypoxia significantly increased atrial ET-1 release and upregulated its ETRA and ETRB concomitantly with potently stimulation of ANP secretion in beating rabbit atria. Hypoxia-induced ANP secretion was obviously attenuated by antagonists of ETRA and ETRB, BQ123 and BQ788. The increase level of pERK induced by hypoxia was reversed by BQ123 as well as BQ788 and ERK inhibitor PD98059 was mimicked the effect of ET receptors antagonists on the regulation of hypoxia-induced ANP secretion. Furthermore, the hypoxia-elevated level of atrial GATA-4 protein was also dramaticly attenuated by antagonists of ET receptors.Conclusions:Acute hypoxia significantly promotes atrial endogenous ET-1 release and which is in turn contributes in the regulation of hypoxia-stimulated ANP secretion through activation of ETR-ERK-GATA-4 signaling pathway.Objective:Lipocalin-type prostaglandin D synthase (L-PGDS) plays an important protective role in the heart under hypoxia and ischemia. However, the effect of L-PGDS on the regulation of hypoxia-induced atrial natriuretic peptide (ANP) secretion is not understood. The present study is to investigate the role of L-PGDS in the hypoxia-induced stimulation of ANP secretion in isolated perfused rabbit atria.Methods:Isolated perfused beating rabbit atrial model was used and levels of ET-1 as well as ANP were measured by radioimmunoassay. The protein level of L-PGDS is determined by western blot analysis.Results:Acute hypoxia significantly increased ANP secretion concomitantly with upregulated expression of L-PGDS. In parallel, acute hypoxia increased atrial endothelin-1 (ET-1) secretion. Hypoxia-induced atrial L-PGDS was dramatically attenuated by antagonists of ET receptors and inhibitors of L-PGDS were mimicked the effect of ET receptors antagonists. In addition, pretreatment of the atria with inhibitors of L-PGDS and endothelin receptors significantly attenuated the hypoxia-induced stimulation of ANP secretion. Combined treatment with inhibitors of L-PGDS and endothelin receptors showed no more effect than individual modulators. Furthermore, inhibitor of L-PGDS was failed to modulation the action of ET-1 on the regulation of ANP secretion as well as atrial dynamics in normal atria and the increase of ET-1 release in hypoxic atria.Conclusion:Results of the present study indicate that ET-1-ETR-L-PGDS pathway is involved in the hypoxia-induced stimulation of ANP secretion in isolated perfused beating rabbit atria.