In order to investigate if slow oscillations in blood pressure are related to oscillations induced by the parasympathetic or sympathetic nervous system, we made a fourier analysis of blood pressure, sympathetic efferent nerve activity (splanchnic nerve activity) and vagal afferent and efferent activity (thoracic vagal nerve activity) in 6 conscious WKY rats. The control measurement was made after a 0.2 ml saline bolus i.v. injection and during a constant saline perfusion of 2 ml/h. In a second protocol we gave a 20 μg bolus injection (0.2 ml) of Metyl-Scopolamine. Thereafter, the measurement began during a constant perfusion of 200 μg/h Metyl-Scopolamine (2 ml/h). One day after these protocols, a bolus infusion of 100 μg Prazosin (0.2 ml) was given. A further measurement was then made during a constant i.v. Prazosin infusion of 3 mg/h (6 ml/h).

To test if the slow frequency oscillations prevail over the entire measuring period, three dimensional plots of frequency vs. power vs. time were performed (10 min. at 40 Hz). In the blood pressure plots two peaks were regularly found: one coinciding with the heart rate (between 6-7 Hz) and another corresponding to oscillations in sympathetic and vagal nerve activity at 0.5-1.5 Hz. The latter peak was blunted by Metyl-Scopolamine and the frequency of these oscillations were shifted to the right (1.5-2.5 Hz). During application of Prazosin the oscillations remained in vagal and sympathetic nerve activity, however the corresponding blood pressure peak was accentuated in its power.

In conclusion, blood pressure, sympathetic nerve activity and vagal nerve activity have corresponding slow frequency oscillations. The oscillations in blood pressure can be blunted by blockade of the parasympathetic system and augmented by sympathetic blockade.