The effect of changes in blood volume on low frequency blood pressure fluctuations in spontaneously hypertensive rats

This study is based on the hypothesis that the development of essential hypertension is due to a defect in cardiovascular control. Young, prehypertensive, spontaneously hypertensive (SHR) rats were compared with normotensive Wistar Kyoto (WKY) rats. Spectral analysis of blood pressure (ABP) fluctuations previously demonstrated that baseline low-frequency fluctuations (0.04-0.1 Hz) are reduced in the SHR rats even before they develop hypertension. In the present study, 20-min-long ABP traces were sampled with the focus on frequencies as low as 0.004 Hz. The effect caused by a perturbation in blood pressure was investigated in young SHR versus WKY rats. A sudden drop in blood volume (2-ml bleeding) caused a clear increase in low-frequency ABP fluctuations, more pronounced in SHR than in WKY rats. The decrease in mean ABP was larger in SHR (-42%) than in WKY rats (-21%). Alpha₁ -blockade (prazosin) affected the reaction of both species to bleeding differently. The results indicate that the SHR rats exhibit an abnormal nervous response (α-sympathetic) to a drop in blood pressure, which might be at the basis of the development of hypertension