BEAT-TO-BEAT FLUCTUATIONS IN THE BP RELATED SIGNALS IN RATS - CAN IT CONTRIBUTE TO THE UNDERSTANDING OF THE DEVELOPMENT OF HYPERTENSION

The goal of this study was to investigate the alterations in blood pre ssure control in young spontaneously hypertensive rats (SHR), as refle cted in the power distribution of blood pressure fluctuations. We stud ied six SHR preceding the onset of overt hypertension, compared to six age matched control rats, the normotensive Wistar-Kyoto rats (WKY), a nd analyzed the power density distribution of several blood pressure r elated signals, namely: arterial blood pressure (ABP), systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP) an d heart rate (HR). ABP fluctuations exhibited a basic difference in th e power distribution pattern between the strains: at low frequencies ( < 0.15 Hz) more power was observed in WKY than in SHR, while in the (0 .35-1.00 Hz) range, more power was observed in SHR. These significant differences in patterns which existed at baseline, were abolished by p razosin (2.5 mg/kg). Observing the power distribution in the BP relate d signals, the patterns were different from that found in the ABP itse lf. At baseline, in SEP and DBP, the most dominant power was located a t low frequencies < 0.04 Hz, like in ABP. However, unlike ABP, the rem ainder of the power was located in the high frequency region (HF: 1.5- 3.0 Hz), mainly in SHR. Prazosin had a marked effect on PP power spect ra; it shifted the power to the HF region in both strains. In PP, powe r spectra differences observed between the strains at baseline in KF w ere eliminated by prazosin. This seems to indicate that, in SHR compar ed to WKY, respiratory fluctuations which are low at baseline in PP, a re a mechanical reflection of the higher sympathetic tone in SHR befor e alpha(1) sympathetic blockade. This study supports previous findings in which differences in cardiovascular control occur in SHR already a t the prehypertensive stage. The above results suggest that alpha(1) s ympathetic control is altered in the SHR strain, and therefore, when t his limb is blocked, some of the differences between the strains disap pear. Furthermore, the analysis of the BP related signals enable us to identify alterations existing in the control mechanisms in SHR, which involve adjunct control mechanisms enhanced under alpha(1) sympatheti c blockade. Finally, an important result is, that for all BP related s ignals under study, excluding HR, the response to alpha(1)-blockade re duces the power density in the 0.07-0.15 Hz region indicating that thi s region is directly associated with the activity of alpha control. (C ) 1998 Elsevier Science B.V. All rights reserved.