The baroreflex constitutes the only hitherto known buffer of rapid arterial blood pressure fluctuations. In order to investigate the influence of sinoaortic and cardiopulmonary baroreflex pathways and nitric oxide (NO) on the dynamic properties of short- term blood pressure control, we determined the power spectra of 24h- blood pressure time series of adult, conscious, freely moving foxhounds under a normal sodium diet. This was done in the intact state (N=6), during blockade of NO-synthesis via a bolus injection of the false substrate NG-nitro-L-arginine ((L-NNA), 16.5±2mg/kg body weight i.v., N=5) and in animals devoid of baroreceptor and cardiopulmonary reflexes (N=5). After L-NNA, blood pressure (BP) increased from 116±4 to 137±6mmHg (P<0.01), heart rate decreased by roughly 30beats/min to 68±3beats/min (P<0.01). The power of spontaneous fluctuations in blood pressure within the frequency range of 0.1Hz - 0.5Hz was tripled by L-NNA (P<0.05). By comparison, total sinoaortic and cardiopulmonary denervation increased power of slower oscillations (<0.1Hz) by a factor of 4.7 (P<0.05), whereas the power within 0.1Hz- 0.5Hz was not significantly different from the control values.

It is concluded that NO and the baroreceptor reflex both play an important role as physiological blood pressure buffers. The NO - system influences predominantly rapid (0.1 - 0.5Hz) and the baroreflex slower fluctuations (<0.1Hz) of arterial blood pressure.