HEART RATE VARIABILITY DURING nNOS INHIBITION IN SPONTANEOUSLY HYPERTENSIVE RATS

PURPOSE: The current study investigated role of nitric oxide (NO), produced by neuronal nitric oxide synthase (nNOS) on heart rate variability (HRV) in spontaneously hypertensive rats (SHR). METODS: The selective neuronal nitric oxide synthase (nNOS) inhibition was performed by application of 7-Nitroindazole (7NI) in conscious normotensive Wistar rats (n=10) and in SHR (n=10), intravenously in a dose 2mg/kg/h. Blood pressure wave was registered directly through a femoral artery catheter in a control period and during nNOS inhibition. In spectrograms of heart rate, derived by FFT algorithm, spectral power (P) in the low (LF), mid (MF) and high (HF) frequency band were studied. Throughout relation, PMF/PHF the sympatho-vagal balance was determined. RESULTS: The nNOS derivate NO in Wistar rats decreased PMF from 1.39±0.34 to 0.43±0.03 ms, p<0.05 and altered PMF/PHF ratio from 0.80±0.1 to 0.44±0.03, (p<0.05). In SHR, nNOS inhibition did not affect HRV. CONCLUSIONS: The absence of inhibiting action of nNOS-derived NO on sympathetic neurotransmission in normotensive rats led to a decrease of sympathetically mediated oscillations in heart rate and to displacement of sympatho-vagal balance. The lack of effect of nNOS-derived NO inhibition in SHR on the HRV may be a result of the impaired nNOS signaling pathway in SHR.