Atrial natriuretic peptide-induced inhibition of aldosterone secretion: a quest for mediator(s)

Anti-Hypertensive Activity of Some Selected Unani Formulations: An Evidence-Based Approach for Verification of Traditional Unani Claims Using LC-MS/MS for the Evaluation of Clinically Relevant Blood Parameters in Laboratory Rats

Background: Systemic arterial hypertension, which is associated with an increased risk of cardiovascular disease(CVD), is the most significant modifiable risk factor for mortality and morbidity worldwide. WHO has recognized Unanipathy as an alternate system of medicine. The aim of the present study is to investigate the anti-hypertensive activity of some selected unani formulations using L-NAME model. Method: Group I or hypertensive control group: L-NAME administered for 7 days and left for the next 7 days; Group II or KASgroup: L-NAME administered (i.p) for 7 days and L-NAME + KAS (1000 mg/kg b.w) for the next 7 days; Group III or DMM group: L-NAME administered (i.p) for 7 days and L-NAME + DMM (2000 mg/kg b.w) for the next 7 days; Group IV or MSR group: L-NAME administered (i.p) for 7 days and L-NAME + MSR (300 mg/kg b.w) for the next 7 days; Group V or HJ group: L-NAME administered (i.p) for 7 days and L-NAME + HJ (113 mg/kg b.w) for the next 7 days; Group VI or KGS group: L-NAME administered (i.p) for 7 days and L-NAME +KGS (2000 mg/kg b.w) for the next 7 days. Non-invasive systolic blood pressure and RR-interval (ECG) was measured. Plasma was investigated forsodium, potassium, nitrite, ANP, adrenaline, noradrenaline and aldosterone on day 0, 7 and 14 using LC-MS/MS. Result: Treatment showed a non-significant lowreduction in SBP (systolic blood pressure) of KAS, MSR and HJ while that of DMM was quite significant (p < 0.05), but in the case of KGS, SBP increased. DMM on day 14 significantly (p < 0.05) reduced plasma nitrite while no significant plasma Na+ was noted. In the case of both DMM and KGS, potassium increased significantly (p < 0.05) on day 14. No significant changes in plasma ANP and aldosterone was observed against DMM and KGS while blood levels of adrenaline and noradrenaline significantly (p < 0.05) changed. No significant change in body weight was found. Conclusions: L-NAME KAS, MSR and HJ showed no change in SBP while DMM showed a significant reduction in SBP with decreased plasma nitrite. Probably, DMM may have anti-hypertensive activity mediated through NO inhibition while KGS may involve central sympathomimetic action.

Understanding the Pathobiology of Pulmonary Hypertension Due to Left Heart Disease

The development of pulmonary hypertension (PH) is common and has adverse prognostic implications in patients with heart failure due to left heart disease (LHD), and thus far, there are no known treatments specifically for PH-LHD, also known as group 2 PH. Diagnostic thresholds for PH-LHD, and clinical classification of PH-LHD phenotypes, continue to evolve and, therefore, present a challenge for basic and translational scientists actively investigating PH-LHD in the preclinical setting. Furthermore, the pathobiology of PH-LHD is not well understood, although pulmonary vascular remodeling is thought to result from (1) increased wall stress due to increased left atrial pressures; (2) hemodynamic congestion-induced decreased shear stress in the pulmonary vascular bed; (3) comorbidity-induced endothelial dysfunction with direct injury to the pulmonary microvasculature; and (4) superimposed pulmonary arterial hypertension risk factors. To ultimately be able to modify disease, either by prevention or treatment, a better understanding of the various drivers of PH-LHD, including endothelial dysfunction, abnormalities in vascular tone, platelet aggregation, inflammation, adipocytokines, and systemic complications (including splanchnic congestion and lymphatic dysfunction) must be further investigated. Here, we review the diagnostic criteria and various hemodynamic phenotypes of PH-LHD, the potential biological mechanisms underlying this disorder, and pressing questions yet to be answered about the pathobiology of PH-LHD.

Transgenic Mice Overexpressing Human Alpha-1 Antitrypsin Exhibit Low Blood Pressure and Altered Epithelial Transport Mechanisms in the Inactive and Active Cycles

Human alpha-1 antitrypsin (hAAT) is a versatile protease inhibitor, but little is known about its targets in the aldosterone-sensitive distal nephron and its role in electrolyte balance and blood pressure control. We analyzed urinary electrolytes, osmolality, and blood pressure from hAAT transgenic (hAAT-Tg) mice and C57B/6 wild-type control mice maintained on either a normal salt or high salt diet. Urinary sodium, potassium, and chloride concentrations as well as urinary osmolality were lower in hAAT-Tg mice maintained on a high salt diet during both the active and inactive cycles. hAAT-Tg mice showed a lower systolic blood pressure compared to C57B6 mice when maintained on a normal salt diet but this was not observed when they were maintained on a high salt diet. Cathepsin B protein activity was less in hAAT-Tg mice compared to wild-type controls. Protein expression of the alpha subunit of the sodium epithelial channel (ENaC) alpha was also reduced in the hAAT-Tg mice. Natriuretic peptide receptor C (NPRC) protein expression in membrane fractions of the kidney cortex was reduced while circulating levels of atrial natriuretic peptide (ANP) were greater in hAAT-Tg mice compared to wild-type controls. This study characterizes the electrolyte and blood pressure phenotype of hAAT-Tg mice during the inactive and active cycles and investigates the mechanism by which ENaC activation is inhibited in part by a mechanism involving decreased cathepsin B activity and increased ANP levels in the systemic circulation.

Pathophysiology of Hyponatremia in Children

Hyponatremia is a common electrolyte disorder in children. It is generally defined as plasma sodium of less than 135 mmol/l. Sodium homeostasis is essential for maintaining intravascular volume and is tightly linked to water balance. Plasma water volume is regulated mainly by the secretion of an antidiuretic hormone (ADH) and by the thirst mechanism. ADH is synthesized in the hypothalamus and stored in the posterior hypophysis. It binds to V2 receptors in the distal nephron and induces translocation of aquaporin water channels in the plasma membrane to retain water. There are two main types of receptors involved in the control of the body water balance-osmoreceptors and baroreceptors. Osmoreceptors reside in hypothalamus and respond to changes of extracellular fluid (ECF) osmolality. Baroreceptors are mechanoreceptors that sense blood pressure in the vessel wall. Response reflexes from baroreceptors influence sympathetic outflow, vessel tonus, and cardiac output. An increase of 1% of plasma osmolality may cause an increase in ADH levels, while the threshold of volume receptors for ADH secretion is higher. However, significant hypotension is a more potent stimulus for ADH secretion than increased osmolality. The main cause of pediatric hyponatremia is an abundance of free water. This may occur in hypovolemic children with low ECF volume, normovolemic patients with inappropriately increased ADH secretion, and also in hypervolemic individuals with decreased effective circulating volume and appropriately increased ADH levels. Proper understanding of the pathophysiology of hyponatremic states is essential for establishing the correct diagnosis and appropriate therapy.

Signaling Interactions in the Adrenal Cortex

The major physiological stimuli of aldosterone secretion are angiotensin II (AII) and extracellular K(+), whereas cortisol production is primarily regulated by corticotropin (ACTH) in fasciculata cells. AII triggers Ca(2+) release from internal stores that is followed by store-operated and voltage-dependent Ca(2+) entry, whereas K(+)-evoked depolarization activates voltage-dependent Ca(2+) channels. ACTH acts primarily through the formation of cAMP and subsequent protein phosphorylation by protein kinase A. Both Ca(2+) and cAMP facilitate the transfer of cholesterol to mitochondrial inner membrane. The cytosolic Ca(2+) signal is transferred into the mitochondrial matrix and enhances pyridine nucleotide reduction. Increased formation of NADH results in increased ATP production, whereas that of NADPH supports steroid production. In reality, the control of adrenocortical function is a lot more sophisticated with second messengers crosstalking and mutually modifying each other's pathways. Cytosolic Ca(2+) and cGMP are both capable of modifying cAMP metabolism, while cAMP may enhance Ca(2+) release and voltage-activated Ca(2+) channel activity. Besides, mitochondrial Ca(2+) signal brings about cAMP formation within the organelle and this further enhances aldosterone production. Maintained aldosterone and cortisol secretion are optimized by the concurrent actions of Ca(2+) and cAMP, as exemplified by the apparent synergism of Ca(2+) influx (inducing cAMP formation) and Ca(2+) release during response to AII. Thus, cross-actions of parallel signal transducing pathways are not mere intracellular curiosities but rather substantial phenomena, which fine-tune the biological response. Our review focuses on these functionally relevant interactions between the Ca(2+) and the cyclic nucleotide signal transducing pathways hitherto described in the adrenal cortex.

Endocrine and hypertensive disorders of potassium regulation: primary aldosteronism

The identification of primary aldosteronism as a common cause of resistant hypertension is a significant advance in our ability to care for patients with hypertension. Primary aldosteronism is common, and when unrecognized is associated with an increased incidence of adverse cardiovascular outcomes. Identification of primary aldosteronism is based on use of the plasma aldosterone level, plasma renin activity, and the aldosterone:renin ratio. Differentiation between unilateral and bilateral autonomous adrenal aldosterone production then guides further therapy, with use of mineralocorticoid-receptor blockers for patients with bilateral autonomous adrenal aldosterone production and laparoscopic adrenalectomy for patients with unilateral autonomous aldosterone production. In this review, we discuss in detail the pathogenesis of primary aldosteronism-induced hypertension and potassium disorders, the evaluation of the patient with suspected primary aldosteronism, and the management of primary aldosteronism, both through medications and surgery.

Interactive roles of NPR1 gene-dosage and salt diets on cardiac angiotensin II, aldosterone and pro-inflammatory cytokines levels in mutant mice

OBJECTIVE

The objective of the present study was to elucidate the interactive roles of guanylyl cyclase/natriuretic peptide receptor-A (NPRA) gene (Npr1) and salt diets on cardiac angiotensin II (ANG II), aldosterone and pro-inflammatory cytokines levels in Npr1 gene-targeted (1-copy, 2-copy, 3-copy, 4-copy) mice.

METHODS

Npr1 genotypes included 1-copy gene-disrupted heterozygous (+/-), 2-copy wild-type (+/+), 3-copy gene-duplicated heterozygous (++/+) and 4-copy gene-duplicated homozygous (++/++) mice. Animals were fed low, normal and high-salt diets. Plasma and cardiac levels of ANG II, aldosterone and pro-inflammatory cytokines were determined.

RESULTS

With a high-salt diet, cardiac ANG II levels were increased (+) in 1-copy mice (13.7 ± 2.8 fmol/mg protein, 111%) compared with 2-copy mice (6.5 ± 0.6), but decreased (-) in 4-copy (4.0 ± 0.5, 38%) mice. Cardiac aldosterone levels were increased (+) in 1-copy mice (80 ± 4 fmol/mg protein, 79%) compared with 2-copy mice (38 ± 3). Plasma tumour necrosis factor alpha was increased (+) in 1-copy mice (30.27 ± 2.32 pg/ml, 38%), compared with 2-copy mice (19.36 ± 2.49, 24%), but decreased (-) in 3-copy (11.59 ± 1.51, 12%) and 4-copy (7.13 ± 0.52, 22%) mice. Plasma interleukin (IL)-6 and IL-1α levels were also significantly increased (+) in 1-copy compared with 2-copy mice but decreased (-) in 3-copy and 4-copy mice.

CONCLUSION

These results demonstrate that a high-salt diet aggravates cardiac ANG II, aldosterone and pro-inflammatory cytokine levels in Npr1 gene-disrupted 1-copy mice, whereas, in Npr1 gene-duplicated (3-copy and 4-copy) mice, high salt did not render such elevation, suggesting the potential roles of Npr1 against salt loading.

The ANF-RGC gene motif (669)WTAPELL(675) is vital for blood pressure regulation: biochemical mechanism

ANF-RGC is the prototype membrane guanylate cyclase, both the receptor and the signal transducer of the hormones ANF and BNP. After binding them at the extracellular domain, it, at its intracellular domain, signals activation of the C-terminal catalytic module and accelerates production of the second messenger, cyclic GMP. This, in turn, controls the physiological processes of blood pressure, cardiovascular function, fluid secretion, and others: metabolic syndrome, obesity, and apoptosis. The biochemical mechanism by which this single molecule controls these diverse processes, explicitly blood pressure regulation, is the subject of this study. In line with the concept that the structural modules of ANF-RGC are designed to respond to more than one yet distinctive signals, the study demonstrates the construction of a novel ANF-RGC-In-gene-(669)WTAPELL(675) mouse model. Through this model, the study establishes that (669)WTAPELL(675) is a vital ANF signal transducer motif of the guanylate cyclase. Its striking physiological features linked with their biochemistry are the following. (1) It controls the hormonally dependent cyclic GMP production in the kidney and the adrenal gland. Its deletion causes (2) hypertension and (3) cardiac hypertrophy. (4) These mice show higher levels of the plasma aldosterone. For the first time, a mere seven-amino acid-encoded motif of the mouse gene has been directly linked with the physiological control of blood pressure regulation, a detailed biochemistry of this linkage has been established, and a model for this linkage has been described.

Aldosterone and aldosterone receptor antagonists in patients with chronic heart failure

Aldosterone is a mineralocorticoid hormone synthesized by the adrenal glands that has several regulatory functions to help the body maintain normal volume status and electrolyte balance. Studies have shown significantly higher levels of aldosterone secretion in patients with congestive heart failure compared with normal patients. Elevated levels of aldosterone have been shown to elevate blood pressure, cause left ventricular hypertrophy, and promote cardiac fibrosis. An appreciation of the true role of aldosterone in patients with chronic heart failure did not become apparent until the publication of the Randomized Aldactone Evaluation Study. Until recently, the use of aldosterone receptor antagonists has been limited to patients with severe heart failure and patients with heart failure following myocardial infarction. The Eplerenone in Mild Patients Hospitalization and Survival Study in Heart Failure (EMPHASIS-HF) study added additional evidence to support the expanded use of aldosterone receptor antagonists in heart failure patients. The results of the EMPHASIS-HF trial showed that patients with mild-to-moderate (New York Heart Association Class II) heart failure had reductions in mortality and hospitalizations from the addition of eplerenone to optimal medical therapy. Evidence remains elusive about the exact mechanism by which aldosterone receptor antagonists improve heart failure morbidity and mortality. The benefits of aldosterone receptor antagonist use in heart failure must be weighed against the potential risk of complications, ie, hyperkalemia and, in the case of spironolactone, possible endocrine abnormalities, in particular gynecomastia. With appropriate monitoring, these risks can be minimized. We now have evidence that patients with mild-to-severe symptoms associated with systolic heart failure will benefit from the addition of an aldosterone receptor antagonist to the standard therapies of angiotensin-converting enzyme inhibitors and beta-blockers. This review will address the pharmacologic basis of aldosterone receptor antagonists in patients with heart failure and the clinical impact of this therapy.

Guanylyl cyclase/natriuretic peptide receptor-A gene disruption causes increased adrenal angiotensin II and aldosterone levels

Disruption of the guanylyl cyclase-A/natriuretic peptide receptor-A (GC-A/NPRA) gene leads to elevated arterial blood pressure and congestive heart failure in mice lacking NPRA. This study was aimed at determining whether Npr1 (coding for GC-A/NPRA) gene copy number affects adrenal ANG II and aldosterone (Aldo) levels in a gene-dose-dependent manner in Npr1 gene-targeted mice. Adrenal ANG II and Aldo levels increased in 1-copy mice compared with 2-copy mice, but decreased in 3-copy and 4-copy mice. In contrast, renal ANG II levels decreased in 1-copy (25%), 3-copy (38%), and 4-copy (39%) mice compared with 2-copy mice. The low-salt diet stimulated adrenal ANG II and Aldo levels in 1-copy (20 and 2,441%), 2-copy (15 and 2,339%), 3-copy (20 and 424%), and 4-copy (31 and 486%) mice, respectively. The high-salt diet suppressed adrenal ANG II and Aldo levels in 1-copy (46 and 29%) and 2-copy (38 and 17%) mice. On the other hand, the low-salt diet stimulated renal ANG II levels in 1-copy (45%), 2-copy (45%), 3-copy (59%), and 4-copy (48%) mice. However, the high-salt diet suppressed renal ANG II levels in 1-copy (28%) and 2-copy (27%) mice. In conclusion, NPRA signaling antagonizes adrenal ANG II and Aldo levels in a gene-dose dependent manner. Increased adrenal ANG II and Aldo levels may play an important role in elevated arterial blood pressure and progressive hypertension, leading to renal and vascular injury in Npr1 gene-disrupted mice.

Control of aldosterone secretion: a model for convergence in cellular signaling pathways

Aldosterone secretion by glomerulosa cells is stimulated by angiotensin II (ANG II), extracellular K(+), corticotrophin, and several paracrine factors. Electrophysiological, fluorimetric, and molecular biological techniques have significantly clarified the molecular action of these stimuli. The steroidogenic effect of corticotrophin is mediated by adenylyl cyclase, whereas potassium activates voltage-operated Ca(2+) channels. ANG II, bound to AT(1) receptors, acts through the inositol 1,4,5-trisphosphate (IP(3))-Ca(2+)/calmodulin system. All three types of IP(3) receptors are coexpressed, rendering a complex control of Ca(2+) release possible. Ca(2+) release is followed by both capacitative and voltage-activated Ca(2+) influx. ANG II inhibits the background K(+) channel TASK and Na(+)-K(+)-ATPase, and the ensuing depolarization activates T-type (Ca(v)3.2) Ca(2+) channels. Activation of protein kinase C by diacylglycerol (DAG) inhibits aldosterone production, whereas the arachidonate released from DAG in ANG II-stimulated cells is converted by lipoxygenase to 12-hydroxyeicosatetraenoic acid, which may also induce Ca(2+) signaling. Feedback effects and cross-talk of signal-transducing pathways sensitize glomerulosa cells to low-intensity stimuli, such as physiological elevations of [K(+)] (< or =1 mM), ANG II, and ACTH. Ca(2+) signaling is also modified by cell swelling, as well as receptor desensitization, resensitization, and downregulation. Long-term regulation of glomerulosa cells involves cell growth and proliferation and induction of steroidogenic enzymes. Ca(2+), receptor, and nonreceptor tyrosine kinases and mitogen-activated kinases participate in these processes. Ca(2+)- and cAMP-dependent phosphorylation induce the transfer of the steroid precursor cholesterol from the cytoplasm to the inner mitochondrial membrane. Ca(2+) signaling, transferred into the mitochondria, stimulates the reduction of pyridine nucleotides.

The glyceryl ester of prostaglandin E2 mobilizes calcium and activates signal transduction in RAW264.7 cells

Glyceryl prostaglandins (PG-Gs) are generated by the oxygenation of the endocannabinoid, 2-arachidonylglycerol, by cyclooxygenase 2. The biological consequences of this selective oxygenation are uncertain because the cellular activities of PG-Gs have yet to be defined. We report that the glyceryl ester of PGE(2), PGE(2)-G, triggers rapid, concentration-dependent Ca(2+) accumulation in a murine macrophage-like cell line, RAW264.7. Ca(2+) mobilization is not observed after addition of PGE(2), PGD(2)-G, or PGF(2alpha)-G but is observed after addition of PGF(2alpha). Moreover, PGE(2)-G, but not PGE(2), stimulates a rapid but transient increase in the levels of inositol 1,4,5-trisphosphate (IP(3)) as well as the membrane association and activation of PKC. PGE(2)-G induces a concentration-dependent increase in the levels of phosphorylated extracellular signal regulated kinases 1 and 2 through a pathway that requires the activities of PKC, IP(3) receptor, and phospholipase C beta. The results indicate that PGE(2)-G triggers Ca(2+) mobilization, IP(3) synthesis, and activation of PKC in RAW264.7 macrophage cells at low concentrations. These responses are independent of the hydrolysis of PGE(2)-G to PGE(2).

Guanine nucleotide-binding proteins in aortic smooth muscle from hypertensive rats

To explore the hypothesis that altered vascular muscle signal transduction may underlie some of the vascular changes observed in hypertensive models, we measured expression of GTP-binding protein (G protein) alpha-subunits, Gs, G(i), and Gq, in aortic muscle of reduced renal mass and sham-operated rats and proximal and distal aortic segments from rats with interrenal aortic coarctation (IR-AC). G protein expression was measured by immunoblot analysis. When we probed aortic muscle membrane with G(i) and Gq alpha-subunit antibodies, we identified 41- and 42-kD immunoreactive proteins, respectively. Three immunoreactive bands specific to Gs alpha-subunit antibody were resolved. Immunoreactive blot densities were compared. In aortic muscle membrane of reduced renal mass rats (blood pressure, 148 +/- 7 mm Hg), we found significantly reduced Gs and G(i) blot densities compared with sham-operated controls (blood pressure, 99 +/- 12 mm Hg). There were no differences in Gq blot densities between reduced renal mass and control rats. Gs and G(i) blot densities were significantly lower in IR-AC proximal aortic segments (carotid pressure, 165 +/- 5 mm Hg) and distal aortic segments (femoral pressure, 121 +/- 4 mm Hg) than in aortas of sham-operated controls. In contrast, Gq expression was significantly increased in the high-pressure proximal aortic segments compared with low-pressure distal aortic segments from IR-AC rats. Thus, altered G protein expression occurs in aortic muscle from nongenetic rat models of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)