Endogenous nitric oxide buffers blood pressure variability between
0.2 hz and 0.6 hz in the conscious rat.
Nafz, Benno, Claus D. Wagner, and Pontus B. Persson.
Physiologisches Institut der Humboldt Universit[umlaut]at zu Berlin
(Charit[acute]e)
APStracts 3:0383H, 1996.
Shear?- stress is a potent stimulus for the formation and release of
nitric oxide (NO). It seems therefore possible that a short?- term
increase in arterial blood pressure (BP), which leads to a
concomitant rise in endothelial shear?- stress, enhances NO?-
release. The latter elicits a relaxation of vascular smooth muscle
cells which, in turn, counteracts the initial rise in BP. Thus, this
chain of events may constitute a negative feedback loop reducing
blood pressure variability (BPV). To test this hypothesis, blood
pressure time series were determined via telemetry in freely moving,
conscious Sprague Dawley (SD) rats. Since it was reported recently
that NO?- effects on BP are more pronounced in females, the
experiments were performed on two groups consisting of 10 female and
11 male animals. This was done under control conditions and after
fixing NO?- plasma levels via an i.v. bolus of 15?mg/kg bwt. NG
-nitro-L-arginine methyl ester (L-NAME) together with a continuous
infusion of nitroprusside (15+/-0.8?[mu]g/min). This combined
infusion maintained mean BP and heart rate at physiological levels,
thus avoiding as much as possible interferences with other reflexes,
e.g. the baroreflex. In order to quantitate BPV fast Fourier
transforms of the blood pressure time series were determined. The
absolute power in the frequency range below 1?Hz increased during
fixed NO to about 350% versus control (female control: 2.1*109+/
-1.5*108?mmHg2 vs. fixed NO: 8.0*109+/-1.3*109?mmHg2, P<0.005;
male control: 3.4*109+/-4.6*108?mmHg2 vs. 8.3*109+/-2.0*109?mmHg2,
P<0.05). This was mainly caused by a substantial rise in the
power ranging from 0.2?Hz to 0.6?Hz which increased roughly fourfold
in both females and males. It is concluded, that the NO system is a
potent buffer of spontaneous blood pressure oscillations in the
freely moving rat. This system is most efficient in buffering
frequencies within the range of 0.2?Hz to 0.6?Hz and shows no gender
specific differences with respect to its blood pressure buffering
capacity.
Received 4 March 1996; accepted in final form 6 August 1996.
APS Manuscript Number H207-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996