Variable renal atrial natriuretic factor gene expression in hypertension

Cardiac Natriuretic Peptide Profiles in Chronic Hypertension by Single or Sequentially Combined Renovascular and DOCA-Salt Treatments

The involvement of natriuretic peptides was studied during the hypertrophic remodeling transition mediated by sequential exposure to chronic hemodynamic overload. We induced hypertension in rats by pressure (renovascular) or volume overload (DOCA-salt) during 6 and 12 weeks of treatment. We also studied the consecutive combination of both models in inverse sequences: RV 6 weeks/DS 6 weeks and DS 6 weeks/RV 6 weeks. All treated groups developed hypertension. Cardiac hypertrophy and left ventricular ANP gene expression were more pronounced in single DS than in single RV groups. BNP gene expression was positively correlated with left ventricular hypertrophy only in RV groups, while ANP gene expression was positively correlated with left ventricular hypertrophy only in DS groups. Combined models exhibited intermediate values between those of single groups at 6 and 12 weeks. The latter stimulus associated to the second applied overload is less effective than the former to trigger cardiac hypertrophy and to increase ANP and BNP gene expression. In addition, we suggest a correlation of ANP synthesis with volume overload and of BNP synthesis with pressure overload-induced hypertrophy after a prolonged treatment. Volume and pressure overload may be two mechanisms, among others, involved in the differential regulation of ANP and BNP gene expression in hypertrophied left ventricles. Plasma ANP levels reflect a response to plasma volume increase and volume overload, while circulating BNP levels seem to be regulated by cardiac BNP synthesis and ventricular hypertrophy.

The interplay between chromogranin A-derived peptides and cardiac natriuretic peptides in cardioprotection against catecholamine-evoked stress

Chromogranin A (CgA) is the major soluble protein co-stored and co-released with catecholamines (CAs) from secretory vesicles in the adrenal medulla chromaffin cells. Present in the diffuse neuroendocrine system, it has also been detected in rat and human cardiac secretory granules where it co-stores with natriuretic peptide hormones (NPs). Mounting evidence shows that CgA is a marker of cardiovascular dysfunctions (essential hypertension, hypertrophic and dilatative cardiomyopathy, heart failure) and precursor of the cardioactive peptides vasostatin-1 (VS-1) and catestatin (Cts). This review focuses on recent knowledge regarding the myocardial, coronary and anti-adrenergic actions of VS-1. In particular, the negative inotropism, lusitropism and coronary dilation effects of rat CgA1-64 (rCgA) and human recombinant STACgA1-78 (hrSTACgA1-78) are summarized with attention on their counteracting isoproterenol- and endothelin-1-induced positive inotropism, as well as ET-1-dependent coronary constriction. The interactions between vasostatins (VSs), NPs and CA receptors are proposed as a paradigm of the heart capacity to organize complex connection-integration processes for maintaining homeostasis under intense cardio-excitatory stimuli (myocardial stress).

Local action of endogenous renal tubular atrial natriuretic peptide

Up-regulation of atrial natriuretic peptide (ANP) mRNA in the kidneys in several disorders has been demonstrated; however, evidence that ANP synthesized by the kidney exerts a local function has never been produced. Therefore, we investigated whether endogenous ANP could modulate high glucose-stimulated TGF-beta1, collagen type I and nuclear factor-kappaB (NF-kappaB) in NRK-52E cells using transfection of ANP and ANP small interfering RNA (siANP). NRK-52E cells were grown with or without transfection with ANP plasmid; cells were also transfected with ANP siRNA or control siRNA. These cells were then stimulated with a high glucose concentration to modulate ANP, TGF-beta1, collagen type I, NF-kappaB and IkappaB-alpha, and the results showed that ANP, TGF-beta1, collagen type I and NF-kappaB significantly increased in untransfected cells, and the transfection of ANP significantly attenuated high glucose-activated TGF-beta1, collagen I and NF-kappaB expression. ANP siRNA knocked-down ANP but significantly increased TGF-beta1 and collagen I under normal glucose conditions; ANP siRNA decreased IkappaB-alpha but strongly enhanced high glucose-activated TGF-beta1, collagen type I and NF-kappaB. In contrast, medium from ANP-transfected cells attenuated high glucose-activated TGF-beta1 and collagen type I expression in NRK-52E cells transfected with siANP. In conclusion, our results demonstrated that siANP increased activation of TGF-beta1, collagen type I and NF-kappaB in NRK-52E cells under high glucose conditions, and medium from ANP-transfected cells attenuated high glucose-activated TGF-beta1 and collagen type I. This is the first study to demonstrate the auto/paracrine action of endogenous ANP in renal tubular cells on the attenuation of hyperglycemia-activated TGF-beta1 and NF-kappaB expression. J. Cell. Physiol. 219: 776-786, 2009. (c) 2009 Wiley-Liss, Inc.

Atrial natriuretic peptide behaviour and myocyte hypertrophic profile in combined pressure and volume-induced cardiac hypertrophy

OBJECTIVE

To investigate cardiomyocyte hypertrophy and hormonal profile in cardiac hypertrophy resulting from sequentially applied overloads.

METHODS

We studied Sprague-Dawley rats with renovascular hypertension (RV), where pressure overload predominates, or deoxycorticosterone acetate (DOCA)-salt (DS), where volume overload predominates, at 2 and 4 weeks of treatment, and the combination of both models in inverse sequence: RV 2 weeks/DS 2 weeks (RV2/DS2) and DS 2 weeks/RV 2 weeks (DS2/RV2), and their sham controls (Sh).

RESULTS

Blood pressure and cardiomyocyte diameter increased to a similar extent in RV and DS at 2 and 4 weeks and in combined models. Cardiomyocyte length increased remarkably in the DS4 group. Circulating atrial natriuretic peptide (ANP) was elevated in all hypertensive groups after 2 and 4 weeks. The RV2/DS2 group showed similar plasma ANP levels to RV4, but DS2/RV2 exhibited a three-fold increase in ANP levels (P<0.001 versus Sh4, DS2 and DS4). Atrial ANP mRNA remained unchanged in all groups. DS treatment alone or in combination with RV increased left ventricular ANP mRNA, meanwhile only RV treatment increased left ventricular B-type natriuretic peptide (BNP) mRNA. Ventricular ANP expression levels, but not circulating ANP, correlated with both cardiomyocyte diameter (r=0.859, P<0.01) and length (r=0.848, P<0.01). Renal expression of natriuretic peptide receptor C (NPR-C) was unchanged in RV4 but decreased to a similar extent in the DS4 group and both combined treatments.

CONCLUSION

Morphometric patterns seem to be more related to the paracrine function of the heart than to the secretion of ANP and the endocrine function. Plasma ANP in the DS2/RV2 group could indicate a different evolution of the remodelling process. ANP expression seems to be a more sensitive marker for volume than for pressure overload.

Evidence that the vasodilator angiotensin-(1-7)-Mas axis plays an important role in erectile function

The vasodilator/antiproliferative peptide angiotensin-(1-7) [ANG-(1-7)] is released into the corpus cavernosum sinuses, but its role in erectile function has yet to be defined. In this study, we sought to determine whether ANG-(1-7) and its receptor Mas play a role in erectile function. The ANG-(1-7) receptor Mas was immunolocalized in rat corpus cavernosum by confocal microscopy. Infusion of ANG-(1-7) into corpus cavernosum at a rate of 15.5 pmol x kg(-1) x min(-1) potentiated the elevation of the corpus cavernosum pressure induced by electrical stimulation of the major pelvic ganglion (MPG) in rats. The facilitatory effect of ANG-(1-7) was completely blunted by the specific ANG-(1-7) receptor blocker A-779 and N(omega)-nitro-L-arginine methyl ester. Nitric oxide (NO) release in the corpus cavernosum was evaluated with the fluorescent dye 4-amino-5 methylamino-2',7'-difluorofluorescein diacetate. Electrical stimulated-release of NO in rat corpus cavernosum was potentiated by ANG-(1-7). Furthermore, incubation of rat and mouse corpus cavernosum strips with ANG-(1-7) at 10 nmol/l resulted in an increase of NO release. This effect was completely abolished in mas-deficient mice. More importantly, genetic deletion of Mas resulted in compromised erectile function as demonstrated by penile fibrosis and severely depressed response to electrical stimulation of the MPG. Furthermore, the attenuated erectile function of DOCA-salt hypertensive rats was fully restored by ANG-(1-7) administration. Together these data provide strong evidence for a key role of the ANG-(1-7)-Mas axis in erectile function.

Antihypertensive Effect of 5-HT1A Agonist Buspirone and 5-HT2B Antagonists in Experimentally Induced Hypertension in Rats

We investigated the antihypertensive effect of 5-HT1A agonist (buspirone) and 5-HT2B antagonists (SB204741 and SB200646) in deoxycorticosterone acetate (DOCA)-salt-induced hypertensive rats. Experiments were divided into two sets: in the first set, sham-operated control and DOCA-treated hypertensive rats received buspirone (1 mg/kg/day p.o. for 4 weeks) and in the second set, in vivo and in vitro studies were carried out. In the case of in vivo studies, sham-operated control and DOCA-treated hypertensive rats received SB204741 or SB200646 (1 mg/kg/week i.v. for 4 weeks). Blood pressure was measured weekly by tail-cuff method. After completion of the treatment schedule, blood pressure and vascular reactivity to various agonists like 5-HT, noradrenaline and adrenaline were recorded. Chronic administration of buspirone, SB204741 and SB200646 produced a significant reduction in blood pressure and vascular reactivity to agonists in DOCA-salt hypertensive rats, implying an antihypertensive effect. However, chronic administration of the same drugs in sham control rats did not alter blood pressure and vascular reactivity to various agonists. For in vitro studies a similar treatment schedule was followed as in vivo studies and a cumulative concentration response curve of 5-HT was recorded on isolated thoracic aorta. Treatment with 5-HT2B antagonists shifted the concentration response curve of 5-HT to the right on isolated aorta. We conclude that 5-HT1A agonist and 5-HT2B antagonists possess an antihypertensive effect.

Regulation of renal CYP4A expression and 20-HETE synthesis by nitric oxide in pregnant rats

20-Hydroxyeicosatetraenoic acid (20-HETE), which promotes renal vasoconstriction, is formed in the rat kidney primarily by cytochrome P-450 (CYP) 4A isoforms (4A1, 4A2, 4A3, 4A8). Nitric oxide (NO) has been shown to bind to the heme moiety of the CYP4A2 protein and to inhibit 20-HETE synthesis in renal arterioles of male rats. However, it is not known whether NO interacts with and affects the activity of CYP4A1 and CYP4A3, the major renal CYP4A isoforms in female rats. Incubation of recombinant CYP4A1 and 4A3 proteins with sodium nitroprusside (SNP) shifted the absorbance at 440 nm, indicating the formation of a ferric-nitrosyl-CYP4A complex. The absorbance for CYP4A3 was about twofold higher than that of CYP4A1. Incubation of SNP or peroxynitrite (PN; 0.01-1 mM) with CYP4A recombinant membranes caused a concentration-dependent inhibition of 20-HETE synthesis, with both chemicals having a greater inhibitory effect on CYP4A3-catalyzed activity. Moreover, incubation of CYP4A1 and 4A3 proteins with PN (1 mM) resulted in nitration of tyrosine residues in both proteins. In addition, PN and SNP inhibited 20-HETE synthesis in renal microvessels from female rats by 65 and 59%, respectively. We previously showed that microvessel CYP4A1/CYP4A3 expression and 20-HETE synthesis are decreased in late pregnancy. Therefore, we investigated whether such a decrease is dependent on NO, the synthesis of which has been shown to increase in late pregnancy. Administration of NG-nitro-l-arginine methyl ester (l-NAME) to pregnant rats for 6 days (days 15-20 of pregnancy) caused a significant increase in systolic blood pressure, which was prevented by concurrent treatment with the CYP4A inhibitor 1-aminobenzotriazole (ABT). Urinary NO2/NO3 excretion decreased by 40 and 52% in l-NAME- and l-NAME + ABT-treated groups, respectively. Interestingly, renal microvessel 20-HETE synthesis showed a marked increase following l-NAME treatment, and this increase was diminished with coadministration of ABT. These results demonstrate that NO interacts with CYP4A proteins in a distinct manner and it interferes with renal microvessel 20-HETE synthesis, which may play an important role in the regulation of blood pressure and renal function during pregnancy.

The cellular localization of increased atrial natriuretic peptide mRNA and immunoreactivity in diabetic rat kidneys

Increased intrarenal atrial natriuretic peptide (ANP) mRNA expression has been reported in several disorders. To further investigate the action of renal ANP, we need to elucidate the exact site of its alteration in diseased kidneys. ANP mRNA and ANP were detected by in situ hybridization and immunohistochemistry in the kidneys from five normal and five diabetic rats. Renal ANP mRNA in eight normal and nine diabetic rats was measured by RT-PCR with Southern blot hybridization. In normal and diabetic rats, the distribution of ANP mRNA and ANP-like peptide was mainly located in proximal, distal, and collecting tubules. However, diabetic rats had significant enhancement of ANP mRNA and ANP-immunoreactive staining in the proximal straight tubules, medullary thick ascending limbs, and medullary collecting ducts. ANP mRNA in the outer and inner medulla of nine diabetic rats increased 5.5-fold and 3.5-fold, but only 1.8-fold in the renal cortex. This preliminary study showed that ANP mRNA and ANP immunoreactivity in proximal straight tubules, medullary thick ascending limb, and medullary collecting ducts apparently increased in diabetic kidneys. These findings imply that ANP synthesis in these nephrons may involve in adaptations of renal function in diabetes.

Aquaporin-2 transcript is differentially regulated by dietary salt in Sprague-Dawley and Dahl SS/Jr rats

Aquaporin-2 (AQP-2) is a vasopressin-regulated water channel in the kidney collecting duct. AQP-2 transcript has been identified by transcriptional profiling of rat kidneys as being regulated by dietary salt. We compared renal AQP-2 transcript expression in Sprague-Dawley and Dahl salt-sensitive (SS/Jr) rats using real-time RT-PCR. Expression of AQP-2 transcript is 5-fold less (P<0.01) in the Sprague-Dawley and 3-fold greater in Dahl SS/Jr rats (P<0.01) on high versus basal NaCl diets. The AQP-2 coded sequence was identical in Sprague-Dawley and Dahl SS/Jr rats. The present results provide evidence that: (1)AQP-2 plays a role in salt adaptation and (2) regulation of aquaporin transcript expression by salt is altered in the Dahl SS/Jr rat.

Comparison of angiotensin-converting enzyme (ACE), neutral endopeptidase (NEP) and dual ACE/NEP inhibition on blood pressure and resistance arteries of deoxycorticosterone acetate-salt hypertensive rats

OBJECTIVES

Omapatrilat, an inhibitor of neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE), is an effective antihypertensive agent. Here, we studied the relative roles of NEP and ACE inhibition and their effect on resistance artery structure and function of deoxycorticosterone acetate (DOCA)-salt hypertensive rats.

METHODS

Omapatrilat (40 mg/kg per day), the NEP inhibitor CGS 25462 (CGS, 100 mg/kg per day) and the ACE inhibitor enalapril (10 mg/kg per day), were given for 3 weeks to DOCA-salt hypertensive rats. Effects on small mesenteric resistance arteries were studied on a pressurized myograph. Collagen deposition was evaluated by confocal microscopy.

RESULTS

Systolic blood pressure of DOCA-salt rats was significantly reduced (P < 0.05) by omapatrilat and CGS. Omapatrilat and CGS treatment increased lumen diameter and decreased media width and media/lumen ratio of small arteries of DOCA-salt rats (P < 0.05). Small artery relaxation responses to acetylcholine improved under omapatrilat or CGS treatment. The stress-strain curve shifted leftward in mesenteric arteries from DOCA-salt rats compared to control rats. Omapatrilat or CGS treatment resulted in a rightward shift, which was significantly different from that induced by enalapril. Omapatrilat and CGS decreased collagen deposition in the vessel wall of DOCA-salt rats. Enalapril had no effect on blood pressure, vascular structure, endothelial function or collagen deposition in the vessel wall of DOCA-salt rats.

CONCLUSIONS

Dual inhibition of ACE/NEP in DOCA-salt hypertensive rats resulted in potent anti-hypertensive effects, prevented vascular remodelling and improved endothelial function of resistance arteries. NEP inhibition is involved to a large extent in the effect of omapatrilat in DOCA-salt rats. These actions of omapatrilat may confer protection against end-organ damage characteristic of severe hypertension.