THE CHARACTERISTICS OF ENDOGENOUS OUABAIN SECRETION FROM CULTURED BOVINE ADRENOCORTICAL CELLS

Objective To compare the characteristics or endogenous ouabaln(EO) secretion with the other adrenocortical hormones and determine the effects of angiotensin I (Ang I ), and ad reno corticotrophin (ACTH ) on the secretion or EO. Methods EO was measured by radioimmunoassay from primary cultured bovine adrenocotical cells (BAC). Results oouabain was determined in the media or cultured BAC. Both EO and aldosterone secretion were decreased from the 6uter to inner layer or the cultured adrenal cortex, and the responses to Ang I and ACTH were hlgher than that in the mld layer (P <o. o5) and inner layer (P <o. o1 ). Cortisol secretion was activated by Ang I or ACTH was slgnificantly higher in the mid layer and in the inner layer than that in the outer layer. The tlme-course experlment showed that the gradually rising amounts or aldosterone and cortisol could be determined during the continuous incubation to 48h wlth or without Ang I or ACTH. However, EO did not increase continuously arter 24h or incubation in the basal secreting sltuation and arter 12h of lncubatiou in the stimulating situation by Ang,or ACTH. There were obvlous drops in aldosterone and cortisol secretlou from 3rd day during a 21 day-perlod cell culture, but the peak secretion of ouabain was in 7th day. Conclusion it suggests that the secretory mechanism might be different between EO and aldosterone or cortisol. Also, Ang I and ACTR might be involved in the regulation of Eo secretion.

Angiotensin receptor blocker drugs and inhibition of adrenal beta-arrestin-1-dependent aldosterone production: Implications for heart failure therapy

Aldosterone mediates many of the physiological and pathophysiological/cardio-toxic effects of angiotensin II(Ang II). Its synthesis and secretion from the zona glomerulosa cells of the adrenal cortex, elevated in chronic heart failure(HF), is induced by Ang II type 1 receptors(AT1Rs). The AT1R is a G protein-coupled receptor, mainly coupling to Gq/11 proteins. However, it can also signal through β-arrestin-1(βarr1) or-2(βarr2), both of which mediate G protein-independent signaling. Over the past decade, a second, Gq/11 proteinindependent but βarr1-dependent signaling pathway emanating from the adrenocortical AT1R and leading to aldosterone production has become appreciated. Thus, it became apparent that AT1R antagonists that block both pathways equally well are warranted for fully effective aldosterone suppression in HF. This spurred the comparison of all of the currently marketed angiotensin receptor blockers(ARBs, AT1R antagonists or sartans) at blocking activation of the two signaling modes(G protein-, and βarr1-dependent) at the Ang IIactivated AT1R and hence, at suppression of aldosterone in vitro and in vivo. Although all agents are very potent inhibitors of G protein activation at the AT1R, candesartan and valsartan were uncovered to be the most potent ARBs at blocking βarr activation by Ang II and at suppressing aldosterone in vitro and in vivo in post-myocardial infarction HF animals. In contrast, irbesartan and losartan are virtually G protein-"biased" blockers at the human AT1R, with very low efficacy for βarr inhibition and aldosterone suppression. Therefore, candesartan and valsartan(and other, structurally similar compounds) may be the most preferred ARB agents for HF pharmacotherapy, as well as for treatment of other conditions characterized by elevated aldosterone.

Nicotine-induced adrenal beta-arrestin1 upregulation mediates tobacco-related hyperaldosteronism leading to cardiac dysfunction

BACKGROUND Tobacco-related products,containing the highly addictive nicotine together with numerous other harmful toxicants and carcinogens,have been clearly associated with coronary artery disease,heart failure,stroke,and other heart diseases.Among the mechanisms by which nicotine contributes to heart disease is elevation of the renin-angiotensin-aldosterone system(RAAS)activity.Nicotine,and its major metabolite in humans cotinine,have been reported to induce RAAS activation,resulting in aldosterone elevation in smokers.Aldosterone has various direct and indirect adverse cardiac effects.It is produced by the adrenal cortex in response to angiotensin II(AngII)activating AngII type 1 receptors.RAAS activity increases in chronic smokers,causing raised aldosterone levels(nicotine exposure causes the same in rats).AngII receptors exert their cellular effects via either G proteins or the twoβarrestins(βarrestin1 and-2).AIM Since adrenal?arrestin1 is essential for adrenal aldosterone production and nicotine/cotinine elevate circulating aldosterone levels in humans,we hypothesized that nicotine activates adrenal?arrestin1,which contributes to RAAS activation and heart disease development.METHODS We studied human adrenocortical zona glomerulosa H295R cells and found that nicotine and cotinine upregulateβarrestin1 mRNA and protein levels,thereby enhancing AngII-dependent aldosterone synthesis and secretion.RESULTS In contrast,siRNA-mediatedβarrestin1 knockdown reversed the effects of nicotine on AngII-induced aldosterone production in H295 R cells.Importantly,nicotine promotes hyperaldosteronism via adrenalβarrestin1,thereby precipitating cardiac dysfunction,also in vivo,since nicotine-exposed experimental rats with adrenal-specificβarrestin1 knockdown display lower circulating aldosterone levels and better cardiac function than nicotine-exposed control animals with normal adrenalβarrestin1 expression.CONCLUSION Adrenalβarrestin1 upregulation is one of the mechanisms by which tobacco compounds,like nicotine,promote cardio-toxic hyperaldosteronism in vitro and in vivo.Thus,adrenalβarrestin1 represents a novel therapeutic target for tobaccorelated heart disease prevention or mitigation.