THE BLOOD-PRESSURE BUFFERING CAPACITY OF NITRIC-OXIDE BY COMPARISON TO THE BARORECEPTOR REFLEX

To compare the contribution of nitric oxide (NO) to the buffering of s hort-term and circadian fluctuations of arterial blood pressure with t hat of the baroreceptor reflex, conscious foxhounds were subjected to continuous 24-h blood pressure recordings. A pressure transducer was p laced into the lumen of the abdominal aorta. Telemetry recordings were done under control conditions, following blockade of NO formation by intravenous bolus injection of N-G-nitro-L-arginine (L-NNA; 16.5 +/- 2 mg/kg body wt) and after total sinoaortic and cardiopulmonary denerva tion in five dogs each. L-NNA produced a sustained elevation of mean a rterial pressure (MAP; 137.2 +/- 6.4 mmHg vs. control, 112.9 +/- 3.7 m mHg). After denervation, no significant increase of MAP was found (113 .5 +/- 4.1 mmHg), but the standard deviation of the MAP histogram was significantly greater (22.5 +/- 3.1 vs. 10.6 +/- 0.9 mmHg, P < 0.05). Sequential spectral analysis showed that total power between 0 and 0.5 Hz was elevated more than twofold after L-NNA (P < 0.05). This was du e primarily to increased power in the range above 0.1 Hz. After denerv ation, total power increased about threefold (P < 0.05), almost exclus ively occurring below 0.04 Hz. Power in the range above 0.2 Hz was dim inished, although not significantly. It is concluded that in the consc ious dog, NO, as well as the baroreceptor reflex, is an effective bloo d pressure buffer. NO is most effective above 0.1 Hz, whereas the baro receptors primarily buffer fluctuations slower than 0.04 Hz.