Spectral analysis of renal microcirculation in spontaneously hypertensive rat (SHR) using the new developed wavelet method

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The kidney exhibits an ability to maintain the blood flow and glomerular filtration rate constant when the renal perfusion pressure is altered. Two factors contribute to this autoregulatory response, tubuloglomerular feedback and myogenic response.Previously, the renal autoregulation was studied using the micropuncture technique. In this study, we investigated the renal cortical blood flow using the spectral analysis (Maximum entropy method; MEM and Wavelet method) to determine the role of nitric oxide and angiotensin II on the renal autoregulation in SHR.Methods: Study 1. The chloralose-anesthetized male WKY/Izm, SHR/Izm and SHRSP/Izm (17 weeks old) were used. Renal homodynamic responses to NO synthesis inhibitor (L-NAME; 0.5, 1.0 mg/kg ia) were studied. Renal cortical blood flow (RBF) was measured by the laser-Doppler flowmeter. The spectral analysis of RBF variability was performed using maximum entropy method. TGF oscillations (30-50mHz) were confirmed by furosemide. Study 2. WKY/I … More zm and SHR/Izm were used. Angiotensin II (Ang II; 5, 15, 50, 100 ng/kg/min, 20-min iv) was infused. RBF was analyzed by Wavelet method.Results: (1) Left ventricle and aorta weights were increased in SHRSP. (2) Baseline mean arterial pressure (MAP) was 131±4, 182±3 and 214±3 mmHg in WKY, SHR and SHRSP, respectively. Baseline RBF was 49±1, 39±2, and 36±1 ml/min/100g in WKY, SHR and SHRSP, respectively. L-NAME increased MAP and decreased RBF. (3) L-NAME significantly increased TGF oscillations in WKY and SHR, but did not affect in SHRSP. (4) Wavelet could analyze RBF simultaneously ever 5 sec. Ang II tended to increased TGF oscillations in both strains. Compared with conventional spectrogram approach based on MEM, wavelet analysis yields a better time-frequency resolution.Conclusions: Tubuloglomerular feedback response was attenuated in SHRSP. Nitric oxide did not play a major role in TGF in SHRSP. This disorder of TGF might be affected by target organ damage. These results suggest that the effects of Nitric oxide on renal autoregulation are impaired in SHRSP. Wavelet method provides improved resolution of analysis and can be used as general indexes of TGF oscillations in rats. Less