BLOOD-PRESSURE VARIABILITY IS BUFFERED BY NITRIC-OXIDE

The baroreflex constitutes the only hitherto known buffer of rapid blo od pressure oscillations. In order to investigate the influence of nit ric oxide (NO) and the sinoaortic and cardiopulmonary baroreflex pathw ays on the dynamic properties of blood pressure control, we determined the power spectra of 24-h blood pressure time series of conscious dog s. This was done in the intact state (n = 6), during blockade of NO sy nthesis via the false substrate N-G-nitro-L-arginine ((L-NNA), 16.5 +/ - 2 mg/kg body weight i.v., n = 5) and in animals devoid of barorecept or reflexes (n = 5). After L-NNA, blood pressure (BP) increased by rou ghly 20 mmHg to 137 +/- 6 mmHg(P < 0.01), heart rate decreased from 97 +/- 6 to 68 +/- 3 beats/min (P < 0.01). The power of blood pressure v ariations within the frequency range 0.1-0.5 Hz was tripled by L-NNA ( P < 0.05). By comparison total sinoaortic and cardiopulmonary denervat ion increased power of slower oscillations (< 0.1 Hz) by a factor of 4 .7 (P < 0.05). Thus, NO and the baroreceptor reflex both play an impor tant role as physiological blood pressure buffers, NO for rapid (0.1-0 .5 Hz) and the baroreflex for slower fluctuations (< 0.1 Hz).