Differential responses of frequency components of renal sympathetic nerve activity to arterial pressure changes in conscious rats

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 289; no. 4; pp. R1074 - R1082
• Main Authors: Bertram, Delphine, Orea, Valerie, Chapuis, Bruno, Barres, Christian, Julien, Claude
• Format: Journal Article
• Language: English
• Published: United States 01.10.2005
• Subjects: Adaptation, Physiological - physiology; Animals; Baroreflex - physiology; Blood Pressure - physiology; Computer Simulation; Consciousness - physiology; Heart Rate - physiology; Kidney - blood supply; Kidney - innervation; Kidney - physiology; Male; Models, Cardiovascular; Rats; Rats, Sprague-Dawley; Sympathetic Nervous System - physiology
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00270.2005

Département de Physiologie et Pharmacologie Clinique, Faculté de Pharmacie, Université Claude Bernard Lyon 1, Lyon, France Submitted 14 April 2005 ; accepted in final form 29 May 2005 The present study examined the effects of baroreceptor loading and unloading on the various rhythms present in the renal sympathetic nerve activity (RSNA) of 10 conscious rats. Short-lasting (4–5 min), steady-state decreases (from –10 to –40 mmHg) and increases (from 5 to 30 mmHg) in arterial pressure (AP) were induced by the intravenous infusion of sodium nitroprusside and phenylephrine, respectively. The relationship between changes in AP level and RSNA total power (fast Fourier transform analysis; 0–25 Hz) was characterized by an inverse sigmoid function. Basal AP was located 6.3 mmHg above AP at the midrange of the curve, that is, near the lower plateau. Sigmoid relationships were also observed for spectral powers in the low (LF, 0.030–0.244 Hz), respiratory (0.79–2.5 Hz) and high-frequency (HF, 2.5–25 Hz) bands. In contrast, in the MF band (0.27–0.76 Hz) containing oscillations associated with Mayer waves, the AP-RSNA power relationship showed a bell curve shape with a maximum at 21 mmHg below basal AP. Similarly, changes in RSNA power at the frequency of the heart beat were well characterized by a bell curve reaching a maximum at 22 mmHg below basal AP. Under baseline conditions, LF, MF, respiratory and HF powers contributed 3, 10, 18, and 69% of the total RSNA power, respectively. The pulse-synchronous oscillation of RSNA accounted for only 11 ± 1% of HF power. The contribution of HF power to total power did not change consistently with AP changes. Therefore, most of the baroreflex-induced changes in RSNA are mediated by changes in the amplitude of fast, irregular fluctuations. cardiac-related rhythm; baroreceptor reflex; Mayer waves; spectral analysis Address for reprint requests and other correspondence: Claude Julien, Faculté de Pharmacie, 8, Ave. Rockefeller, 69373 Lyon Cedex 08, France (e-mail: julien{at}univ-lyon1.fr )