Regulation of Natriuretic Peptide Family mRNA Induced by Head-down Suspension in Rats / 항공우주의학회지

BACKGROUND: Head-down suspension (HDS) of rats has been used as a model for the simulation of a microgravity environment. Natriuretic peptide family including atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptides (CNP), and their receptors are responsible for body fluid homeostasis and blood pressure control. However, little is known about the long-term responses and the simultaneous observations of both natriuretic peptide family and their receptors following HDS. This study was analyzed the regulation of cardiac, hypothalamic and renal natriuretic peptides and their receptors 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 -45degrees head-down tilt using the tail-traction technique (HDS rats). This study observed the cardiac, hypothalamic and renal syntheses of natriuretic peptides as a expression of ANP, BNP and CNP mRNA. The mRNA expressions of A-type natriuretic peptide receptor (NPR-A), B-type NPR (NPR-B) and clearance receptor (NPR-C) were also determined. The expressions of natriuretic peptide and their receptor mRNA were measured by reverse transcription-polymerase chain reaction with [32P]-dCTP following 4 weeks of HDS in both control and HDS rats. RESULTS: After 4 weeks of HDS, the expressions of ANP mRNA were significantly decreased in the right atrium and the kidney, and showed the non-significant decreasing trend in the left atrium and the hypothalamus of HDS rats. BNP mRNA expressions were decreased in the heart especially in the left atrium, while its mRNA in the left ventricle was showed the non-significant increasing trend following 4 weeks of HDS. The expressions of CNP mRNA were increased in the hypothalamus and showed the non-significant increasing trend in the kidney of the HDS rats. After 4 weeks of HDS, NPR-A mRNA expressions were decreased in the kidney and hypothalamus, but NPR-C mRNA expression was showed the non-significant increasing trend in the kidney of HDS rats compared with controls. CONCLUSION: These results suggest that the regulation of natriuretic peptide mRNA following 4 weeks of HDS exerts to maintain the blood volume through an attenuation of syntheses in natriuretic peptide family of the heart and the kidney.

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 in Renal Expression of Natriuretic Peptides and Their Receptors mRNA Induced by Head-down Suspension in Rats

BACKGROUND: Head-down suspension (HDS) of rats has been used as a model for the simulation of a microgravity environment. Atrial natriuretic peptide (ANP), C-type natriuretic peptides (CNP) and their receptors are found in the kidney, suggesting that these peptides could play a significant physiological role in the kidney. Therefore, this study was investigated the changes in the adaptations of renal natriuretic peptides and their receptors syntheses after 4 weeks of HDS in rats. METHODS: Unanesthetized, unrestrained, male Sprague-Dawley rats were subjected to either a horizontal position (control rats) or a -45degreeshead-down tilt using the tail-traction technique (HDS rats). This study observed the renal syntheses of natriuretic peptides as a expression of ANP and CNP mRNA, and also determined the expression of A-type natriuretic peptide receptor (NPR-A) mRNA and B-type NPR (NPR-B) mRNA. The expressions of natriuretic peptide and NPR mRNA were measured by reverse transcription-polymerase chain reaction with [(32)P]-dCTP following 4 weeks of HDS in the kidney of both control and HDS rats. RESULTS: After 4 weeks of HDS, the expression of ANP mRNA significantly (P<0.01) decreased, while CNP mRNA expression was showed the non-significant increasing trend in the kidney of HDS rats. NPR-A, which binds with ANP, was significantly (P<0.001) decreased in renal mRNA expression of HDS rats compared with controls. Expression in mRNA of NPR-B, which binds with CNP, showed a slightly decreasing trend in the kidney of rats following HDS. CONCLUSION: These results suggest that the renal adaptation following 4 weeks of HDS exerts to maintain the blood volume and electrolyte balance through attenuation of syntheses in the natriuretic peptide and its binding receptor, especially in ANP rather than in CNP systems.

Effects of Long-Term Head-down Suspension on Changes in Body Weight, Daily Water Intake and Hematological Data in Rats

BACKGROUND: This study was aimed to observe the changes in body weight, water intake and hematological data during and after long-term head-down suspension (HDS) in rats. HDS rats induced by tail suspension has evolved as a useful model for the simulation of a microgravity or zero-gravity environment. METHODS: Unanesthetized, unrestrained, male Sprague-Dawley rats, weighing 230-270 g, were subjected to either a hori-zontal position (control horizontal, CH rats) or a 45 degreeshead-down suspension (HDS rats) for 4 weeks. We deter-mined the body weight and daily water intake in both CH and HDS rats. Hematological data including white and red blood cell counts, hemoglobin concentration and hematocrit were measured. The characteristics of red blood cell were also calculated from above hematological data in the both rats after 4 weeks of observa-tion. RESULT: In CH rats, body weight was significantly increased (P<0.05) after 4 weeks of experiment, where-as the body weight of HDS rats was only showed a small increase but was significantly decreased (P<0.05) after 4 weeks of HDS compared with that of CH rats. Daily water intake was increased (P<0.05) after 2 week in HDS rats but the overall changes of the rest period were no difference between both CH and HDS rats. White blood cell counts did not show any changes in both rat groups while red blood cell counts showed a decreas-ing trend after 4 weeks HDS. After HDS, hemoglobin concentration, hematocrit and mean corpuscular hemoglobin were significantly decreased (P<0.05) compared with CH rats. CONCLUSION: These results represent that the long-term HDS could attenuate the increase in body weight of young rats and induce the decrease in hemato-logical data, especially in the characteristics of red blood cell.

Cardiac expressions of natriuretic peptide mRNA following 4 weeks of head-down suspension in rat

BACKGROUND: Head-down suspension (HDS) of rats has evolved as a useful model for the simulation of a microgravity environment. Atrial natriuretic peptides (ANP) and brain natriuretic peptide (BNP) have been considered to comprise the cardiac natriuretic peptide family responsible for body fluid homeostasis and blood pressure control. However, little is known about the long-term responses and the simultaneous observations of both ANP and BNP following HDS. Therefore, this study was aimed to characterize the long-term adaptations of cardiac ANP and BNP syntheses to 4 weeks of HDS in rats. METHOD: Unanesthetized, unrestrained, male Sprague-Dawley rats were subjected to either a horizontal position (control rats) or a 45degree head-down tilt using the tail-traction technique (HDS rats). We determined the cardiac synthesis of natriuretic peptides as a expression of ANP and BNP mRNA, The expressions of natriuretic peptide mRNA were measured by reverse transcription-polymerase chain reaction with [32P]-dCTP following 4 weeks of HDS in the each cardiac chamber of control and HDS rats. RESULT: After 4 weeks of HDS, the expressions of ANP mRNA were decreased in the both right (p<0.05) and left atria. The ANP mRNA in the ventricles did not show significant changes compared with control values. In contrast with ANP, BNP mRNA was only decreased in the left atrium (p<0.05) and revealed the non-significant decreasing trend in the right ventricle. There were no remarkable changes of BNP mRNA expression compared with control rats in the both right atrium and left ventricle. CONCLUSION: Collectively, these results represent that the cardiac syntheses of natriuretic peptides following 4 weeks of HDS are attenuated to prevent any decrement of body fluid as a long-term adaptive response to simulated microgravity and ANP and BNP genes have the differential expression in the each chamber of the heart.

Mechanism of Renal Oxidative Damage following 4-week Head-down Suspension in Rats

The purpose of this study was to observe the variation of malondialdehyde (MDA), an indirect index of oxidative damage, following 4-week of head-down suspension (HDS) at -45degreein rats as a model of simulated weightlessness. We also measured the activities of antioxidant enzymes, such as superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase for clarifying the mechanisms of renal oxidative damage. MDA was increased (p<0.05) at the 4th week of HDS rats compared to control horizontal positioned rats. Following HDS, the renal activity of SOD was also significantly increased (p<0.01) at the 4th week of HDS whereas the changes of renal GSH-Px and catalase activities were not significantly different from controls. The expression of renal SOD mRNA used by polymerase-chain reaction method showed the similar pattern with the change of renal SOD activity and was more increased (p<0.05) than control horizontal positioned rat. These results indicate that simulated weightlessness induces the augmented SOD gene expression in the kidney which results in increased SOD activity, and thus increased production of MDA due to increased production of hydrogen peroxide. And under this condition, GSH-Px and catalase do not play their protective roles against hydrogen peroxide.

Expression of Atrial Natriuretic Peptide mRNA during 2 Weeks of Head-down Suspension in Rats

The aim of this study was to determine the adaptation of atrial natriuretic peptide(ANP) to simulated weightlessness. The level of immunoreactive plasma ANP level and the expression of right atrial ANP mRNA were assessed in male Sparague-Dawley rats during 2 weeks of head-down suspension(HDS) The rats were placed in a -45 degrees anti-orthostatic position. The plasma ANP level was investigated by radioimmunoassay and ANP mRNA was expressed by Northern blot analysis. The changes in daily water intake, body weight and arterial hematocrit did not show the statistical significances during HDS. The plasma ANP level slightly increased after 1 day of HDS, the response was transient and then decreased below the control levels. The expression of the ANP mRNA increased after 1 day, the peak value occurred at 3 days of HDS and thereafter ANP mRNA showed the similar patterns compared to the changes of plasma level. On the basis of these findings, we conclude that the initial adaptation of ANP to increased control blood volume in rats occurs between 3 and 7 days of HDS, and the ANP acts an important role during regulatory process to central hypervolemia at both synthetic and secretory levels within the early stage of HDS.

Activities of Hepatic Antioxidant Enzymes in Rats during 14 Days of Head-down Suspension as a Model of Simulated Weightlessness

Cells and tissues of human and animal are protected against free radicals by several complex mechanisms including the action of antioxidant enzymes, such as superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase. There had been a few reports that simulated or actual weightlessness induced the decrease in activity of antioxidant enzymes and the increase in lipid peroxidation, The purpose of this study was to observe the time-course variation of antioxidant enzymes activities in rats during 14 days of head-down suspension(HDS) at -45 degrees as a model of simulated weightlessness. During HDS, the hepatic activity of SOD significantly decreased (p<0.05) at 3 day of HDS and then maintained a lower value compared to control horizontal position, GSH-Px activity also significantly decreased (p<0.05) at 3 and 7 day of HDS, thereafter showed a slight increasing trend to control horizontal value. The activity of hepatic catalase increased during HDS and the value at the end of HDS showed significant increase (p<0.05). From these results, there is a possibility that weightlessness induce the increase of oxygen free radicals according to the decrease of some antioxidant enzyme activities. The main scavenger to oxygen free radicals is operated via catalase system in rats during HDS. Therefore, we suggest that it is necessary to administrate the antioxidants for protection of the body against oxygen free radicals during first 1 week after exposure of weightlessness, at least.