Atrial secretion of ANP is suppressed in renovascular hypertension: shifting of ANP secretion from atria to the left ventricle

Herbal medicine Oryeongsan (Wulingsan): Cardio-renal effects via modulation of renin-angiotensin system and atrial natriuretic peptide system

Background

Oryeongsan (Wulingsan, Goreisan) has long been used for the treatment of impaired body fluid metabolism. However, the action mechanisms have not been clearly defined. Recently, effects of Oryeongsan on the body fluid and Na+ metabolism and the action mechanisms have been shown more clearly. The present review focuses on the recent findings on the effects of Oryeongsan in the cardio-renal system in relation with body fluid metabolism and action mechanisms leading to a decrease in blood pressure in animal models of hypertension.

Methods

The new and recent findings were searched by using searching systems including PubMed-NCBI and Google-Scholar.

Results

Oryeongsan induced an increase in glomerular filtration rate, and natriuresis and diuresis with a decreased osmolality and resulted in a contraction of the body fluid and Na+ balance. These findings were associated with a suppression of abundance of Na+-H +-exchanger isoform 3 expression and V2 receptor/aquaporin2 water channel signaling pathway in the kidney. Further, treatment with Oryeongsan accentuated atrial natriuretic peptide secretion in the atria from spontaneously hypertensive rats in which the secretion was suppressed. In addition, Oryeongsan ameliorated impaired vasodilation in spontaneously hypertensive rats.

Conclusion

The effects of Oryeongsan in the kidney, atria, and vessel were accompanied by a suppression of AT1 receptor and concurrent accentuation of abundance of AT2/Mas receptors expression and modulation of the natriuretic peptide system in these organs from hypertensive rats. The review shows multiple sites of action of Oryeongsan and mechanisms involved in the regulation of volume and pressure homeostasis in the body.

Amelioration of Hypertension by Oryeongsan through Improvements of Body Fluid and Sodium Balance: Roles of the Renin-Angiotensin System and Atrial Natriuretic Peptide System

Oryeongsan (Wulingsan in China and Goreisan in Japan), a formula composed of five herbal medicines, has long been used for the treatment of imbalance of the body fluid homeostasis in Asian countries. However, the mechanism by which Oryeongsan (ORS) improves the impaired body fluid and salt metabolism is not clearly defined. The present study was performed to define the role of the cardiorenal humoral system in the ORS-induced changes in blood pressure and renal function in hypertension. Experiments were performed in normotensive and two-kidney, one-clip hypertensive rats. Changes in the fluid and salt balance were measured in rats individually housed in metabolic cages. Changes in the systemic and local renin-angiotensin system (RAS) and cardiac natriuretic peptide hormone system (NPS) were evaluated. ORS water extract was administered by oral gavage (100 mg/kg daily) for 3 weeks. ORS induced diuresis and natriuresis along with an increase in glomerular filtration rate and downregulation of the Na⁺/H⁺ exchanger 3 (NHE3) and aquaporin 2 expression in the renal cortex and medulla, respectively. Furthermore, treatment with ORS significantly decreased systolic blood pressure with contraction of body sodium and water accumulation in hypertensive rats. ORS-induced changes were accompanied by modulation of the RAS and NPS, downregulation of the systemic RAS and cardiorenal expression of angiotensin-converting enzyme (ACE) and angiotensin II subtype 1 (AT₁) receptor, and upregulation of the plasma ANP concentration and cardiorenal expression of ANP, ACE2, Mas receptor, and AT₂ receptor. These findings indicate that ORS induces beneficial effects on the high blood pressure through modulation of the RAS and NPS of the cardiorenal system, suppression of the prohypertensive ACE-AT₁ receptor pathway and NHE3, accentuation of the antihypertensive ACE2-Mas axis/AT₂ receptor pathway in the kidney, suppression of the systemic RAS, and elevation of the plasma ANP levels and its synthesis in the heart. The present study provides a biological basis for the use of ORS in the treatment of impaired volume and pressure homeostasis.

Oryeongsan (Wulingsan) ameliorates impaired ANP secretion of atria from spontaneously hypertensive rats

Oryeongsan (ORS), a herbal medicine formula, has long been used for the treatment of impaired body water balance in Asian countries. Recently, it was shown that ORS administration modulates the renin-angiotensin system (RAS). Purpose of the present study was to determine characteristics of atrial ANP secretion and effects of ORS on the secretion in the atria from spontaneously hypertensive rats (SHR). Normotensive WKY groups (WKY-V, WKY-ORS, WKY-LOS) and hypertensive SHR groups (SHR-V, SHR-ORS, SHR-LOS) treated with vehicle, ORS, and losartan as a positive control group, respectively, were used. Experiments were performed in perfused beating atria (1.3 Hz) allowing atrial distension, acetylcholine (ACh) stimulation, and serial collection of atrial perfusates. The secreted ANP concentration was measured using radioimmunoassay. Interstitial fluid (ISF) translocation was measured using [³H]inulin clearance. Stepwise increase in atrial distension by 1.1, 2.0, and 2.7 cmH₂O above basal distension further increased ANP secretion proportionally in the atria from WKY-V, but the response was significantly suppressed in the atria from SHR-V. Cardiomyocyte ANP release, the first step of atrial ANP secretion, was suppressed in the atria from SHR-V compared to those from WKY-V (-8.02 ± 2.86, -15.86 ± 2.27, and -20.09 ± 3.62%; n = 8, for SHR-V vs. 8.59 ± 2.81, 15.65 ± 7.14, and 38.12 ± 8.28%; n = 8, for WKY-V; p < 0.001 for all stepwise distension, respectively). Chronic treatment with ORS reversed the suppressed ANP release in atria from SHR-ORS group (6.76 ± 3.92, 9.12 ± 2.85, and 28.79 ± 1.79% for SHR-ORS; n = 5 vs. SHR-V; n = 8; p = 0.01, p < 0.001, p < 0.001, respectively). The effects of ORS were comparable to those of losartan. Trans-endocardial translocation of ISF, the second step of atrial ANP secretion was similar in the atria from the hypertensive SHR-V and normotensive WKY-V. ACh-induced ANP secretion and cardiomyocyte ANP release were also suppressed in the atria from SHR-V compared to WKY-V and ORS reversed the suppression. These findings were accompanied with accentuation of the AT₁ receptor expression and suppression of the AT₂/Mas receptor, M₂ mACh receptor and GIRK4, a molecular component of K_ACh channel, expression in the atria from SHR-V. Further, treatment with ORS or losartan reversed the expressions in the groups of SHR-ORS and SHR-LOS. These results show that ANP secretion is suppressed in the atria from SHR in association with accentuation of AT₁ receptor and suppression of AT₂/Mas receptor and K_ACh channel expression. Treatment with ORS ameliorates impaired ANP secretion through improving cardiomyocyte ANP release with modulation of the cardiac RAS and muscarinic signaling. These findings provide experimental evidence which supports the effect of ORS on the regulation of atrial ANP secretion in the atria from SHR.

Deterioration of diabetic nephropathy via stimulating secretion of cytokines by atrial natriuretic peptide

BACKGROUND

Atrial natriuretic peptide (ANP) is a cardiovascular and metabolic hormone that has been identified recently as being associated with chronic kidney disease (CKD) without diabetes. Cytokines such as interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and adiponectin (ADP) contribute to the development of type 2 diabetes (T2DM). The aim here was to investigate the relationships of ANP with cytokine levels and clinical variables in T2DM nephropathy patients.

METHODS

A total of 81 participants with T2DM were recruited, including 37 patients with normoalbuminuria, 23 patients with microalbuminuria and 21 patients with macroalbuminuria. Serum concentrations of ANP and cytokines were measured using enzyme-linked immunosorbent assay (ELISA) kits. The correlations between ANP and clinical variables were analyzed. Multiple linear regression and logistic regression models were constructed to test the associations between ANP and the severity and presence of albuminuria.

RESULTS

The macroalbuminuria patients exhibited higher plasma levels of ANP, TNF-α, IL-6, and ADP; higher serum creatinine (Cr) and blood urea nitrogen (BUN); and longer duration of diabetes mellitus (DM) than the patients with normoalbuminuria and microalbuminuria. Plasma ANP level was significantly associated with TNF-α (r = 0.876, p < 0.001), IL-6 (r = 0.816, p < 0.001) and ADP (r = 0.772, p < 0.001), independent of the duration of DM or the BUN concentration.

CONCLUSION

ANP is higher in type 2 diabetes mellitus nephropathy subjects, especially those who have macroalbuminuria, which is associated with compensatory responses to inflammation.

Synthesis and Excretion of Atrial Natriuretic Peptide in Secretory Cardiomyocytes in Experimental Hypertension

The intensity of accumulation and excretion of atrial natriuretic peptide in myocytes of the right atrium in rat models of renovascular hypertension and salt loading was studied by immunocytochemical analysis and transmission electron microscopy. The data suggest that high BP is not the decisive factor affecting secretion of atrial natriuretic peptide in atrial cardiomyocytes. The regulatory mechanisms of the accumulation and release of the peptide from myocyte granules can vary and depend on the pathogenesis of hypertension.