Increased renal ANP synthesis, but decreased or unchanged cardiac ANP synthesis in water-deprived and salt-restricted rats

Mid-regional pro-atrial natriuretic peptide levels before and after hemodialysis predict long-term prognosis

BACKGROUND

Mid-regional pro-atrial natriuretic peptide (MR-proANP) is a strong prognostic biomarker in cardiovascular disease but there is limited data for its use among patients undergoing dialysis.

METHODS

This was a cohort study of patients receiving maintenance hemodialysis from two Danish centers. Blood sampling and echocardiography were performed before and after a dialysis session. We calculated the area under the curve (AUC) for the receiver operating characteristics for diagnosing heart failure and Cox regressions for cardiovascular events and all-cause mortality.

RESULTS

Of the 306 patients, 284 (93%) had MR-proANP measurements both before and after dialysis. Median concentration was 642 pmol/L (IQR 419-858) before and 351 pmol/L (IQR 197-537) after dialysis, a mean decrease of 330 pmol/L (43%, CI 296-364, P < 0.001). MR-proANP concentration both before and after dialysis was negatively correlated to left ventricular ejection fraction with no difference in predictive ability for heart failure, AUC before and after dialysis were 0.60 (CI 0.50-0.70) and 0.61 (CI 0.51-0.71) (P = 0.40). Median follow-up was 32 months (IQR 31-33), during which 99 patients (32%) had a cardiovascular event and 110 (36%) died. A doubling of MR-proANP concentration was associated with a hazard ratio (HR) of 1.6 (CI 1.3-1.9) before and 1.7 (CI 1.4-2.0) after dialysis for mortality and a HR of 1.5 (CI 1.2-1.9) before and 1.4 (CI 1.2-1.7) after dialysis for cardiovascular events (all P < 0.001).

CONCLUSION

The MR-proANP concentration is elevated among patients undergoing hemodialysis and decreases during dialysis. MR-proANP concentration both before, after and intra-dialysis change strongly predicted cardiovascular events and all-cause mortality.

Sex- and age-dependent differences in the hormone and drinking responses to water deprivation

Maintenance of the volume and osmolality of body fluids is important, and the adaptive responses recruited to protect against osmotic stress are crucial for survival. The objective of this work was to compare the responses that occur in aging male and female rats during water deprivation. For this purpose, groups of male and female Wistar rats aged 3 mo (adults) or 18 mo (old) were submitted to water deprivation (WD) for 48 h. The water and sodium (0.15 M NaCl) intake, plasma concentrations of oxytocin (OT), arginine vasopressin (AVP), corticosterone (CORT), atrial natriuretic peptide (ANP), and angiotensin II (ANG II) were determined in hydrated and water-deprived animals. In response to WD, old male and female rats drank less water and saline than adults, and both adult and old females drank more water and saline than respective males. Dehydrated old animals displayed lower ANG II plasma concentration and CORT response compared with the respective normohydrated rats. Dehydrated adult males had higher plasma ANP and AVP as well as lower CORT concentrations than dehydrated adult females. Moreover, plasma OT and CORT levels of old female rats were higher than those in the dehydrated old male rats. Relative expression of ANG II type 1 receptor mRNA was decreased in the subfornical organ of adult and old male rats as well as adult female rats in response to WD. In conclusion, the study elucidated the effect of sex and age on responses induced by WD, altering the degree of dehydration induced by 48 h of WD.

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.

Natriuretic peptide/natriuretic peptide receptor-A (NPR-A) system has inhibitory effects in renal fibrosis in mice

OBJECT

This study was designed to examine whether natriuretic peptide/natriuretic peptide receptor-A (NPR-A) system attenuates renal fibrosis in a unilateral ureteral obstruction (UUO) model and also examined the mechanism involved.

METHODS

Three groups were studied: untreated UUO in wild-type mice; untreated UUO in NPR-A KO mice; and ANP treated (0.05 microg/kg/min) UUO in wild-type mice. We measured histological and immunohistochemical findings (alpha-SMA and F4/80), tissue cGMP levels, various mRNA expression levels by real-time PCR analysis, and transcription factor levels (AP-1 and NF-kappaB) in renal tissue.

RESULTS

Compared with wild-type UUO mice, NPRA-KO UUO mice had abnormal morphological findings (fibrous area: +26%, alpha-SMA expression: +30%) with lower tissue cGMP levels and increases in the mRNA expression levels of TGF-beta, collagen I, collagen III, PAI-1, renin and angiotensinogen, whereas there were no differences in F4/80 positive cells or the mRNA expression levels of ICAM-1, osteopontin, or MCP-1 between the two groups. In contrast, ANP pre-treatment significantly improved morphological changes with increase of tissue cGMP levels and reduction in the mRNA expression level of TGF-beta, collagen I, collagen III, PAI-1, ICAM-1, osteopontin, MCP-1, renin, and angiotensinogen. NPRA-KO UUO mice had higher AP-1 levels than wild-type UUO mice and ANP pre-treatment reduced AP-1 and NF-kappaB activity.

CONCLUSION

The endogenous natriuretic peptide/NPR-A system may inhibit renal fibrosis partly via inhibition of the angiotensin/AP-1/TGF-beta/collagen pathway and exogenous ANP pre-treatment may inhibit it partly via both the angiotensin/AP-1/TGF-beta/collagen and NF-kappaB/inflammatory pathways.

Atrial natriuretic peptide attenuates high glucose-activated transforming growth factor-beta, Smad and collagen synthesis in renal proximal tubular cells

Atrial natriuretic peptide, besides its role in the regulation of volume homeostasis, has been noted to exert cytoprotective effects in several cell types from hypoxia. The present study was performed to explore the effect of ANP on high glucose-activated transforming growth factor-beta1 (TGF-beta1), Smad and collagen synthesis in renal proximal epithelial cells. Cultured NRK-52E cells were divided into five groups: (1) normal glucose (5.5 mM), (2) high glucose (35 mM), (3) D-mannitol (29.5 mM), (4) high glucose plus ANP (10(-6)-10(-9) M), and (5) high glucose plus ANP (10(-6) M) and guanylate cyclase inhibitor LY83583 (10(-7) M) groups. Messenger RNA levels of TGF-beta1, Smad2, and collagens were measured by RT-PCR. ELISA, immunocytochemistry and Western blotting were used to detect protein levels of TGF-beta1, Smad2, phospho-Smad 2/3 and collagen type 1. We found high glucose to significantly increase mRNA levels of TGF-beta1, Smad 2, collagen types I and III and protein levels of TGF-beta1, phospho-Smad 2/3 and collagen type 1, but mannitol did not affect their expression. The addition of ANP significantly attenuated high glucose-enhanced mRNA and protein levels of TGF-beta1, Smad and collagens. LY83583 blocked the influence of ANP on high glucose-activated TGF-beta1, Smad and collagen synthesis. This is the first study to demonstrate that activation of TGF-beta1, Smad and collagen synthesis stimulated by high glucose can also be inhibited by exogenous ANP in renal tubular epithelial cells.

Influence of intravenously administered leptin on nitric oxide production, renal hemodynamics and renal function in the rat

We investigated the effect of leptin on systemic nitric oxide (NO) production, arterial pressure, renal hemodynamics and renal excretory function in the rat. Leptin (1 mg/kg) was injected intravenously and mean arterial pressure (MAP), heart rate (HR), renal blood flow (RBF) and renal cortical blood flow (RCBF), were measured for 210 min after injection. Urine was collected for seven consecutive 30-min periods and blood samples were withdrawn at 15, 45, 75, 105, 135, 165 and 195 min after leptin administration. Leptin had no effect on MAP, HR, RBF, RCBF and creatinine clearance, but increased urine output by 37.8% (0-30 min), 32.4% (31-60 min) and 27.0% (61-90 min), as well as urinary sodium excretion by 175.8% (0-30 min), 136.4% (31-60 min) and 124.2% (61-90 min). In contrast, leptin had no effect on potassium and phosphate excretion. Plasma concentration of NO metabolites, nitrites + nitrates (NOx), increased following leptin injection at 15, 45, 75 and 105 min by 27.7%, 178.1%, 156.4% and 58.7%, respectively. Leptin increased urinary NOx excretion by 241.6% (0-30 min), 552.6% (31-60 min), 430.7% (61-90 min) and 88.9% (91-120 min). This was accompanied by increase in plasma and urinary cyclic GMP. These data indicate that leptin stimulates systemic NO production but has no effect on arterial pressure and renal hemodynamics.

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.

The effect of water deprivation on the expression of atrial natriuretic peptide and its receptors in the spinifex hopping mouse, Notomys alexis

This study investigated the mRNA expression of the atrial natriuretic peptide (ANP) system (peptide and receptors) during water deprivation in the spinifex hopping mouse, Notomys alexis, a native of central and western Australia that is well adapted to survive in arid environments. Initially, ANP, NPR-A and NPR-C cDNAs (partial for receptors) were cloned and sequenced, and were shown to have high homology with those of rat and mouse. Using a semi-quantitative multiplex PCR technique, the expression of cardiac ANP mRNA and renal ANP, NPR-A, and NPR-C mRNA was determined in 7- and 14-day water-deprived hopping mice, in parallel with control mice (access to water). The levels of ANP mRNA expression in the heart remained unchanged, but in the kidney ANP mRNA levels were increased in the 7-day water-deprived mice, and were significantly decreased in the 14-day water-deprived mice. NPR-A mRNA levels were significantly higher in 7-day water-deprived mice while no change for NPR-A mRNA expression was observed in 14-day water-deprived mice. No variation in NPR-C mRNA levels was observed. This study shows that water deprivation differentially affects the expression of the ANP system, and that renal ANP expression is more important than cardiac ANP in the physiological adjustment to water deprivation.

Effects of amlodipine and lacidipine on cardiac remodelling and renin production in salt-loaded stroke-prone hypertensive rats

1. Calcium channel blockers (CCBs) are anti-hypertensive drugs that are usually considered to act mainly as vasodilators. We investigated the relation between the reduction of blood pressure evoked by two long-acting CCBs and their protective effect against cardiac and renal damage in salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP). 2. SHRSP were exposed to high dietary salt intake (1% NaCl in drinking solution) from 8 to 14 weeks of age, with or without amlodipine or lacidipine at three dosage regimens producing similar effects on blood pressure. 3. The lowest dosages of both drugs had non-significant effects on blood pressure but inhibited the paradoxical increases in plasma renin activity (PRA) and in renin mRNA in kidney that were found in salt-loaded SHRSP. The lowest dosage of lacidipine (but not of amlodipine) restored the physiological downregulation of renin production by high salt and reduced left ventricular hypertrophy and mRNA levels of atrial natriuretic factor and transforming growth factor-beta1. 4. The intermediate dosages reduced blood pressure and PRA in a comparable manner, but cardiac hypertrophy was more reduced by lacidipine than by amlodipine. 5. Although the highest doses exhibited a further action on blood pressure, they had no additional effect on cardiac hypertrophy, and they increased PRA and kidney levels of renin mRNA even more than in the absence of drug treatment. 6. We conclude that reduction of blood pressure is not the sole mechanism involved in the prevention of cardiac remodelling by CCBs, and that protection against kidney damage and excessive renin production by low and intermediate dosages of these drugs contributes to their beneficial cardiovascular effects.

Up-regulation of adrenal cortical and medullary atrial natriuretic peptide and gene expression in rats with deoxycorticosterone acetate-salt treatment

Our previous study demonstrated that human adrenal medulla is a site of atrial natriuretic peptide (ANP) synthesis. To further evaluate the role of adrenal ANP in body fluid homeostasis, we investigated the changes in adrenal ANP in rats receiving deoxycorticosterone acetate (DOCA)-salt treatment. In situ hybridization and immunohistochemical study showed that adrenal ANP messenger RNA (mRNA) and ANP-like immunoreactivities (ANP-LI) were mainly localized in the zona glomerulosa and medulla of vehicle-treated rats. DOCA-salt treatment activated ANP mRNA and peptide expression in all adrenal zones, especially in the zona fasciculata/reticularis from 12 h to the entire 8-day study period. Using a semiquantitative RT-PCR technique, the relative quantities of ANP mRNA in the adrenals of the DOCA-salt-treated group were significantly increased from 1 to 8 days, whereas the adrenal weights of DOCA-salt-treated rats were significantly decreased from day 2 to day 8. Our results are the first to indicate that ANP is synthesized not only in the adrenal medulla but also in the adrenal cortex and their syntheses are markedly increased in DOCA-salt-treated rats. These results imply that adrenal ANP may participate in the intraadrenal regulation of adrenal function on water-electrolyte homeostasis in an autocrine or paracrine manner.

Increased nitric oxide synthase mRNA expression in the renal medulla of water-deprived rats

Increased nitric oxide synthase mRNA expression in the renal medulla of water-deprived rats.

BACKGROUND

Experiments were performed to investigate whether renal nitric oxide synthase (NOS) mRNA and protein expression are responsive to the alteration of body volume.

METHODS

Four days of water deprivation (WD) was initiated in 16 male Wistar rats, and 16 normal rats (NC) served as the control group. Neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS) mRNAs and immunoreactivity were measured by reverse transcription-polymerase chain reaction (RT-PCR) followed by Southern blot hybridization and immunohistochemistry, respectively. Plasma angiotensin II, vasopressin, and atrial natriuretic peptide (ANP) concentrations were measured by radioimmunoassay.

RESULTS

The four-day WD increased plasma sodium and osmolality levels, but severely decreased daily urine sodium excretion and urine volume. Plasma angiotensin II and vasopressin concentrations were increased, but the plasma ANP level was significantly decreased in WD rats. nNOS, eNOS, and iNOS mRNA levels were increased by 5.2-, 3.3-, and 3. 4-fold in the outer medulla and 1.7-, 1.5-, and 1.8-fold in the inner medulla, whereas no significant difference was found in the renal cortex of WD rats as compared with NC rats. Additionally, immunohistochemistry revealed that the immunostaining intensity of nNOS, eNOS, and iNOS was clearly enhanced in the medullary thick ascending limb, proximal straight tubule, inner medullary collecting duct, and proximal convoluted tubule in WD rats. Kidney angiotensin II content as well as renin mRNA levels in renal cortex, outer medulla, and inner medulla in WD rats were apparently increased.

CONCLUSIONS

Our results indicate that the increases of nNOS, eNOS, and iNOS synthesis in the kidney, particularly in the renal medulla, may have a role in the adaptation of renal function to volume depletion in the face of an increase of systemic and intrarenal vasoconstrictive substances.