Endogenous renin and related short-term blood pressure variability in the conscious rat

This study was designed to investigate, by use of spectral analysis, the bl ood pressure variability changes induced in the conscious rat by activation of plasmatic renin activity. Rats were surgically prepared with a supra-re nal catheter inserted via the left carotid artery to perform the infusions, and with a femoral artery catheter to measure blood pressure and heart rat e. Secretion of renin was induced using beta-adrenoceptor stimulation produ ced by isoprenaline. A first group (n = 8) was infused with isoprenaline: 0 .003, 10, 100 and 300 ng/kg/min, at a rate of 20 mu l/min. A second group ( n = 8) was given a bolus injection of the angiotensin AT(1) receptor antago nist, valsartan (2 mg/kg, i.a.), prior to isoprenaline infusions. The lack of effect of infusion per se was checked in additional animals (n = 8) infu sed with saline only (20 mu l/min). Five other groups of animals were prepa red with arterial catheters as mentioned previously. Each group received on e concentration of infused isoprenaline and samples of blood were collected for further determinations of plasma renin activity and catecholamine conc entrations. Blood pressure recordings were analysed using the fast Fourier transform on 2048 points time series (204.8 s). Isoprenaline increased plas ma renin activity and did not modify plasma catecholamine concentrations. T he low-frequency (0.02-0.2 Hz) component of the systolic blood pressure var iability was amplified by isoprenaline (10 ng/kg/min isoprenaline: 4.16 +/- 0.62 mm Hg-2 vs. 2.90 +/- 0.44 mm Hg-2 for control value, P < 0.05), a con centration that did not alter either blood pressure or heart rate levels. I soprenaline lowered blood pressure and increased heart rate, starting at co ncentrations of 100 ng/kg/min. Valsartan, whose principal effect was genera tion of tachycardia (+ 25 bpm) modified neither blood pressure levels nor b lood pressure variability. Valsartan prevented the amplification of the low -frequency oscillations of systolic blood pressure induced by isoprenaline (10 ng/kg/min isoprenaline: 2.53 +/- 0.38 mm Hg-2 vs. 2.20 +/- 0.25 mm Hg-2 for control value (valsartan, ns). We conclude that a moderate increase of plasma renin activity enhanced systolic blood pressure variability in the low-frequency range, without affecting blood pressure and heart rate levels . (C) 2000 Elsevier Science B.V. All rights reserved.