Myocardial angiotensin receptor type 1 gene expression in a rat model of cardiac volume overload.

To investigate the regulation of the angiotensin receptor type 1 (AT1) in different organs in cardiac volume overload, we measured AT1 mRNA content in the atria, left and right ventricle, kidney and liver of rats with an aortocaval shunt, produced by infrarenal aortocaval puncture 4 weeks earlier. For angiotensin receptor mRNA quantitation a novel quantitative PCR procedure based on liquid phase hybridization was used that allowed the determination of absolute AT1 mRNA copy numbers and its comparison in different organs. Glyceraldehydephosphate dehydrogenase (GAPDH) mRNA was measured by RT-PCR to control externally equal mRNA content and quality of RNA extraction in shunt animals and controls. Heart weight was increased in the shunt animals, with the greatest increase in the atria. Blood pressure, plasma renin activity, plasma angiotensin I and II and aldosterone concentrations were not significantly altered. The AT1 mRNA content was significantly increased in the atria (shunt: 1167 +/- 350 copies AT1 mRNA/ng RNA vs controls: 803 +/- 240; p < 0.05). No change was found in the right or left ventricle, in the kidney and liver. The findings document that atrial hypertrophy in cardiac volume overload parallel with a significant increase in atrial AT1 mRNA content.