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 -45°head-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 [32P]-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.
Head-down suspension,ANP,CNP,Natriuretic peptide receptor,mRNA,Kidney