Differences in vasomotor control as expressed by changes in the diastolic decay constant in normotensive versus spontaneously hypertensive rats

In order to characterize vasomotor control, the authors studied the compensatory changes in the diastolic decay constant (/spl tau/) caused by abrupt changes in arterial blood pressure (ABP). According to the Windkessel model, /spl tau/ depends on vascular resistance and compliance. For each BP pulse, the authors computed /spl tau/ by parametrical estimation. Conscious, 4 months old, spontaneously hypertensive rats (SHR) were compared to normotensive controls (WKY). Bolus injections of vasoconstrictor, and vasodilator were used to induce abrupt changes in ABP. The response /spl Delta//spl tau/ to changes in mean ABP (/spl Delta/MBP) was observed at baseline and under vagal and /spl beta/-sympathetic blockade. Gain and time delays of /spl Delta//spl tau/ vs. /spl Delta/MBP were extracted. SHR, had higher mean /spl tau/ than WKY. SHR also had reduced gain and shorter delay times, for /spl Delta/MBP>0, and higher delay times for /spl Delta/MBP<0. Blockade abolished these differences. The authors´ findings thus suggest that in SHR vasomotor regulation is abnormal.