[Activation of the renin-angiotensin system and blood pressure variability in rats]

This study was designed to assay, using spectral analysis, the influence of the renin-angiotensin system activation on the blood pressure variability. Rats were surgically prepared with a supra-renal catheter inserted via the left carotid artery to perform local infusions and with a femoral artery catheter to measure blood pressure (BP) and heart rate (HR). The beta-adrenoceptors stimulation by isoprenaline was used to increase the plasma renin activity (PRA). A first group (n = 8) was infused with isoprenaline (0, 0.003, 10, 100, 300 ng/kg/min) at a rate of 20 microL/min. A second group (n = 8) received a bolus of the angiotensin II (AII) AT1 receptor-antagonist valsartan (2 mg/kg/mL, i.a.) prior to isoprenaline infusions. Five groups were used for blood sampling (one group infused with one concentration of isoprenaline) to assay PRA and catecholamines (CA). BP recordings were analysed using the fast Fourier transforms (FFT) on 2048 points time series (204.8 s). Isoprenaline from the concentration of 10 ng/kg/min increased PRA with a maximum effect of 8.5 fold with the highest concentration (300 ng/kg/min, p < 0.05); CA were not modified. Isoprenaline amplified the low-frequency (LF: 0.02-0.20 Hz) component of the systolic BP (SBP) variability (10 ng/kg/min: 4.16 +/- 0.62 mmHg2 versus: 2.90 +/- 0.44 mmHg2 for control value, p < 0.05) even if it did not modify BP and HR levels. Isoprenaline lowered BP and had a tachycardic effect at concentrations > or = 100 ng/kg/mL (at 100 ng/kg/mL: SBP = 115 +/- 3 mmHg, HR = 464 +/- 15 bpm, versus control: SBP = 128 +/- 3 mmHg, HR = 351 +/- 7 bpm, p < 0.05). Valsartan modified neither BP levels nor BP variability but exerted a tachycardic effect (+25 bpm, p < 0.001). Valsartan prevented the amplification of the LF oscillations of SBP induced by isoprenaline (10 ng/kg/min: 2.53 +/- 0.38 mmHg2 versus: 2.20 +/- 0.25 mmHg2 for control value (valsartan), ns). We conclude that a moderate endogenous production of renin increases SBP variability in the LF range in the conscious rat. This effect which does not affect BP and HR levels is mediated by AII AT1 receptors and does not involve the sympathetic nervous system.