Contribution of the renin-angiotensin and kallikrein-kinin systems to short-term variability of blood pressure in two-kidney, one-clip hypertensive rats

Abstract

Spectral analysis was recently chosen to characterize the fast oscillations, depending on the autonomic nervous system, in heart rate and blood pressure variabilities. Humoral stimuli could impinge on the low-frequency domain of blood pressure variability since the time lag to humoral system activation is greater. This study was designed to analyse low-frequency components of short-term variability of blood pressure of conscious rats in conditions where humoral systems were activated. We studied rats with two-kidney, one-clip Goldblatt hypertension in which the blood pressure level was dependent upon the renin-angiotensin and kallikrein-kinin systems. Spectral powers of the systolic and diastolic blood pressure and heart rate were computed in the high (respiratory)-, mid (0.2-0.6 Hz)- and low (0.02-0.2 Hz)-frequency bands, as detected by the fast Fourier transform technique in consecutive 102-s stationary periods. Hypertensive rats exhibited a marked low-frequency component of systolic (+261%) and diastolic (+169%) blood pressure variabilities when compared to sham-operated animals. First, losartan, a selective non-peptide angiotensin AT1 receptor antagonist, reduced this low-frequency component (-44% and -25% for systolic and diastolic blood pressure). In a second series of hypertensive rats, HOE 140, D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]bradykinin, a bradykinin B2 receptor antagonist, decreased the low-frequency component of systolic (-28%) and diastolic (-40%) blood pressure. Losartan, added after HOE 140, induced a supplementary decrease of the low-frequency component (-60% and -42% for systolic and diastolic blood pressure). After the combined blockade, the low-frequency components of systolic and diastolic blood pressure variabilities of the hypertensive rats were equivalent to those of the control rats. Two-kidney, one-clip hypertension was also associated with an elevation of the mid-frequency component of the systolic blood pressure (+55%). The administration of HOE 140 did not change this component while losartan, alone or added after HOE 140, led to an increase (around +100%) in mid-frequency oscillations of systolic blood pressure. The high-frequency oscillations of systolic blood pressure were increased by losartan in the two series of hypertensive rats. Losartan increased the mid-frequency component of heart rate variability in sham-operated rats while the heart rate variability was not modified during any of the treatment periods in two-kidney, one-clip rats. In conclusion, an increase in the low-frequency component of blood pressure variability was observed in a model of hypertension where the blood pressure is dependent upon humoral activities. The reduction of the slow fluctuations following the combined blockade of the kallikrein-kinin and the renin-angiotensin systems suggested the contribution of these humoral systems to this low-frequency component of blood pressure variability.