SYMPATHECTOMY AND CARDIOVASCULAR SPECTRAL COMPONENTS IN CONSCIOUS NORMOTENSIVE RATS

We examined the extent to which sympathetic influences are reflected b y spectral powers of blood pressure and pulse interval in specific fre quency bands in spontaneously behaving Wistar-Kyoto rats subjected to continuous intraarterial blood pressure recording. The rats were pretr eated with 6-hydroxydopamine (150 mg/kg twice in 1 week, n=19) to prod uce chemical sympathectomy or received vehicle (n=15). In the sympathe ctomized group, additional monitoring sessions were performed with rat s under alpha-adrenergic receptor blockade with phenoxybenzamine (n=8) , beta-receptor blockade with propranolol (n=7), or cholinergic recept or blockade with atropine (n=8). Blood pressure signals were analyzed by a computer to calculate spectral powers (fast Fourier transform) in the low-frequency (0.025 to 0.1 Hz), mid-frequency (0.1 to 0.6 Hz), a nd high-frequency (0.8 to 3.0 Hz) bands. In sympa thectomized rats, lo w-frequency power of blood pressure was 70% greater than in intact rat s, whereas mid-frequency power was 60% smaller (P<.05 for both) and hi gh-frequency power was unchanged. High-frequency power of pulse interv al was also unchanged in sympathectomized rats, whereas low- and mid-f requency powers were reduced by approximately 50% (P<.05). No further alterations in spectral powers were observed by adding alpha- or beta- adrenergic blockade to sympathectomy, whereas adding cholinergic block ade caused a striking reduction in all pulse interval powers. Thus, mi d-frequency blood pressure power depends on sympathetic but also to a substantial extent on nonsympathetic influence influences do not contr ibute to low-frequency blood pressure power, having instead a restrain ing effect. The low- and mid-frequency pulse interval powers depend on both sympathetic and vagal influences. Thus, no blood pressure or pul se interval power in the mid- and low-frequency ranges can be regarded as a specific marker of sympathetic activity.