Blood pressure variability in established L-NAME hypertension in rats

Methods Blood pressure variability was evaluated in conscious Wistar control rats and rats with established L-NAME hypertension (20 mg/kg pr 24 h, 4 weeks). Results Final systolic arterial pressure was 185 +/- 5 and 132 +/- 4 mmHg in the N-omega-nitro-L-arginine methyl ester (L-NAME)-treated and control rats, respectively, The standard deviation of systolic arterial pressure in the L-NAME group was 70% greater than in the control rats, indicating a significant increase in the overall variability. Arterial pressure in the L-NAME rats exhibited aperiodical, abrupt rises and falls and data was grossly non-stationary. Blood pressure variability was therefore evaluated using Poincare plot analysis. The variance of the difference (delta) between two successive values of systolic arterial pressure, determined for time intervals of 0.2 to 5 s (0.2 s increment), was always significantly higher in the L-NAME group compared with untreated animals. The variance of delta systolic arterial pressure increased with the time interval and plateaued for time intervals of 2.4 and 1.4 s in hypertensive and normotensive rats, respectively. These differences vanished when the sudden events observed in L-NAME rats were omitted in the construction of Poincare plots. Acute administration of prazosin (1 mg/kg), but not losartan (10 mg/kg) markedly reduced the variance of delta systolic arterial pressure in hypertensive rats. Conclusions Nitric oxide participates in the control of arterial pressure variability. The sympathetic nervous system seems to be a major determinant of the increased short-term variability of arterial pressure in this model. (C) Lippincott Williams & Wilkins.