Blood pressure variability in conscious spontaneously hypertensive rats during endothelin A receptor inhibition

Spontaneously hypertensive rats (SHR) and normotensive Wistar rats were treated with the endothelin(A) (ET(A)) receptor antagonist BQ-123 16.4 nmol/kg.min i.v. at an infusion rate of 25 microl/min for 50 min. Blood pressure was measured in the femoral artery with a Gould/Statham P23ID transducer connected to the computerized data acquisition system Biopac MP100WS. Values of interpulse interval, systolic, diastolic and mean arterial pressure were determined in every heart cycle. Spectrum analysis of systolic, diastolic and mean arterial pressure and interpulse interval variabilities was performed using fast Fourier transform algorithm. In contrast to normotensive rats, BQ-123 infusion in SHR increased mid-frequency band in systolic, diastolic and mean arterial pressure (p < 0.05). The baroreflex sensitivity obtained by the alpha-coefficient in the mid-frequency region (square root of the relation PMFIPI/PMFSAP in msec/mmHg) did not differ between Wistar and SHR before and during BQ-123 administration. Endogenous endothelin acting via endothelin(A) receptors modulates the effects of the sympathetic nervous system on the variations of systolic, diastolic and mean arterial pressure in the hypertensive state. This interrelation between endogenous endothelin and the sympathetic nervous system is not dependent on the arterial baroreflex and is most likely to be realized locally on the vessel level.