Changes in Hypothalamic Expressions of Natriuretic Peptide mRNA following Head-down Suspension in Rats

BACKGROUND: Head-down suspension (HDS) of rats has been used as a model for simulation of a microgravity environment. C-type natriuretic peptides (CNP) and atrial natriuretic peptide (ANP) are produced in the central nervous system, especially in hypothalamus, to complement their peripheral natriuretic effects. Therefore, this study investigated the changes in the central adaptations of hypothalamic ANP and CNP syntheses to 4 weeks of HDS in rats. METHODS: Unanesthetized, unrestrained, male Sprague-Dawley rats were subjected to either a horizontal position (control rats) or a -45 degrees head-down tilt using the tail-traction technique (HDS rats). We determined the hypothalamic syntheses of natriuretic peptides as an expression of ANP and CNP mRNA. The expression of natriuretic peptide mRNA was measured by reverse transcription-polymerase chain reaction with [32P]-dCTP following 4 weeks of HDS in the hypothalamus of control and HDS rats. RESULTS: After 4 weeks of HDS, the expression of ANP mRNA showed a decreasing trend in the hypothalamus of HDS rats. In contrast with ANP, CNP mRNA expression was significantly (p<0.01) increased in the hypothalamus of HDS rats. There were different changes in the hypothalamic CNP and ANP mRNA expressions of HDS rats compared with that of the control rats.CONCLUSION: These results represent that the hypothalamic syntheses of natriuretic peptides are differently responded and the role of CNP is augmented to compensate for the decrement of ANP action in the central nervous system following 4 weeks of HDS.

Changes of mRNA and Plasma Levels of Atrial Natriuretic Peptide in Subtotal Nephrectomized Rats after High Salt Intake / 대한신장학회잡지

High salt intake produces volume expansion and electrolyte imbalance in chronic renal failure and modifies the synthesis and secretion of atrial natriuretic peptide(ANP) to compensate the abnormalities in fluid and sodium handling. This study was performed to investigate the effect of high salt intake on modulation of cardiac and noncardiac ANP mRNA as well as plasma ANP levels in 5/6 subtotal nephrectomized (NPX) rats as a model of chronic renal failure. Adult male Sprague-Dawley rats were divided into sham and NPX rats. NPX rats were induced by 2/3 pole ligation and contralateral nephrectomy. Sham and NPX rats had access to normal chow with tap water for 8 weeks or normal chow with 0.45% NaCl solution(HS) for last 2 weeks. Plasma ANP levels were measured by radioimmunoassay. ANP mRNA from the right atrium, left ventricle, hypothalamus and kidney were analyzed by RT-PCR with 32P-dCTP at 8 weeks after surgical operation in both sham and NPX rats. Blood urea nitrogen(BUN) was measured to evaluate impaired renal function. Body weight, daily water intake, hemoglobin, red blood cell, hematocrit, arterial pressure and heart rate were also monitored. Arterial pressure in NPX+HS rat was significantly increased. Both percent increase of body weight and hematologic findings were decreased in NPX rats. Daily water intake was increased in NPX rats, especially in NPX+HS rat. BUN also increased in NPX rats. Plasma ANP concentration was significantly increased in sham+HS rat, but other significant increases were not shown in NPX rats. The levels of right atrial ANP mRNA represented the increasing trend like as plasma ANP. Left ventricular ANP mRNA was increased in sham+HS rat, while the level in NPX+HS rat was decreased comparing with that of sham+HS rat. Hypothalamic ANP mRNA was decreased in NPX+HS rat. In the kidney, the level of ANP mRNA in sham+HS rat was increased comparing with sham rat, but ANP synthesis in NPX+HS rat was significantly lower than in sham, sham+HS and in NPX rats. These findings represent that the high salt intake in NPX rat does not alter the plasma levels and cardiac synthesis of ANP but suppresses the renal ANP mRNA. The diminished renal ANP synthesis may attenuate the regulatory role of ANP system in the kidney and result in volume expansion and hypertension.

Expression of Atrial and Extra-atrial ANP mRNA in Rats with Chronic Renal Failure / 대한신장학회잡지

Chronic renal failure(CRF) may lead to fluid retention and electrolyte imbalance, and consequently increases the extracellular volume and blood pressure. These changes can trigger secretion and synthesis of atrial natriuretic peptide(ANP) as a compensatory regulator for increases in the glomerular filtration rate and excretion of water and sodium due to the reduced number of functional nephrons. ANP may exert important regulatory role on body fluid balance and blood pressure in CRF. We assessed changes in gene expression of atrial and extra-atrial ANP associated with progression of renal failure in subtotal nephrectomized rats. Adult male Sprague-Dawley rats were divided into sham and CRF rats. CRF rats were induced by 5/6 subtotal nephrectomy. We determined the plasma ANP level using by radioimmunoassay and the ANP mRNA from the right atrium, left ventricle, hypothalamus and kidney were measured by reverse transcription-polymerase chain reaction with 32P- dCTP at 8 wk in sham, and at 8 and 12 wk in CRF rats. Serum urea nitrogen(SUN) was also checked as an indicator of impaired renal function. SUN was significantly increased in CRF rats and the level was higher at CRF 12 wk rat than CRF 8 wk rat. Plasma concentration of ANP also increased in CRF rats compared with sham rat, but was not statistically significant. Altered patterns of ANP mRNA expression were different in each tissue. Right atrial and renal ANP mRNA expressions were slightly increased in CRF rats. Left ventricular ANP mRNA was significantly increased in CRF 8 wk rat compared with sham rat and maintained high at CRF 12 wk rat. However hypothalamic ANP mRNA expressions at CRF rats were decreased and the expression in CRF 12 wk was significantly lower than that at CRF 8 wk. SUN showed positive correlations with expression in left ventricular and renal ANP mRNA, but had a significant negative relationship with hypothalamic ANP mRNA. Plasma ANP concentration was positively correlated with the ANP mRNA expressions in both right atrium and kidney. The present study demonstrated that ANP mRNA in the right atrium, left ventricle, kidney and hypothalamus were differentially expressed upon CRF. This suggests that roles of the local ANP in these tissues are regulated by different mechanisms to compensate the fluid and electrolyte imbalance in rats with experimental chronic renal failure.

Atrial mRNA and Plasma Levels of Atrial Natriuretic Peptides in Rats with Chronic Renal Failure / 대한신장학회잡지

The aim of this study was to assess the adaptive changes in plasma level of atrial natriuretic peptide(ANP) and its atrial mRNA expression in experimental rat model of chronic renal failure(CRF). Male Sprague-Dawley rats weighing 250-300g were divided into control rats, sham operated rats and 5/6 nephrectomized rats. CRF was induced by 5/6 nephrectomy, in that two thirds of the left kidney was ligated and the contralateral kidney was removed 1 week later. In the rats with 2/3 pole ligation, there were no significant changes in mean arterial pressure(MAP), heart rate, BUN and serum creatinine compared to sham operated rats. Expression of atrial ANP mRNA showed initially higher values and plasma renin activity(PRA) was lower than the sham operated rats. After 5/6 nephrectomy, MAP, heart rate, BUN and serum creatinine increased, and PRA showed the sustained lower values than the control rats. The changing pattern of plasma ANP level was similar to the that of ANP mRNA expression that showed biphasic peaks with the first increase at 1 to 3 days and the second increase at 28 days after nephrectomy. There were a significant positive correlation between plasma ANP level and MAP, and a negative correlation between plasma ANP and PRA. These results suggest that the secretion and the synthesis of ANP respond rapidly to the reduced renal mass, and ANP may play an important regulatory role during the renal adapting process in rats with experimental CRF.