Energy Deregulation Precedes Alteration in Heart Energy Balance in Young Spontaneously Hypertensive Rats: A Non Invasive In Vivo 31P-MR Spectroscopy Follow-Up Study

Introduction Gradual alterations in cardiac energy balance, as assessed by the myocardial PCr/ATP-ratio, are frequently associated with the development of cardiac disease. Despite great interest for the follow-up of myocardial PCr and ATP content, cardiac MR-spectroscopy in rat models in vivo is challenged by sensitivity issues and cross-contamination from other organs. Methods Here we combined MR-Imaging and MR-Spectroscopy (Bruker BioSpec 9.4T) to follow-up for the first time in vivo the cardiac energy balance in the SHR, a genetic rat model of cardiac hypertrophy known to develop early disturbances in cytosolic calcium dynamics. Results We obtained consistent P-31-spectra with high signal/noise ratio from the left ventricle in vivo by using a double-tuned (P-31/H-1) surface coil. Reasonable acquisition time (< 3.2min) allowed assessing the PCr/ATP-ratio comparatively in SHR and age-matched control rats (WKY): i) weekly from 12 to 21 weeks of age; ii) in response to a bolus injection of the beta-adrenoreceptor agonist isoproterenol at age 21 weeks. Discussion Along weeks, the cardiac PCr/ATP-ratio was highly reproducible, steady and similar (2.35 +/- 0.06) in SHR and WKY, in spite of detectable ventricular hypertrophy in SHR. At the age 21 weeks, PCr/ATP dropped more markedly (-17.1%+/- 0.8% vs. -3,5%+/- 1.4%, P< 0.001) after isoproterenol injection in SHR and recovered slowly thereafter (time constant 21.2min vs. 6.6min, P< 0.05) despite similar profiles of tachycardia among rats. Conclusion The exacerbated PCr/ATP drop under beta-adrenergic stimulation indicates a defect in cardiac energy regulation possibly due to calcium-mediated abnormalities in the SHR heart. Of note, defects in energy regulation were present before detectable abnormalities in cardiac energy balance at rest.