Baroreflex control of lumbar and renal sympathetic nerve activity in conscious rats

Abstract

Kanbar R, Chapuis B, Oréa V, Barrès C, Julien C. Baroreflex control of lumbar and renal sympathetic nerve activity in conscious rats. Am J Physiol Regul Integr Comp Physiol 295: R8 -R14, 2008. First published April 30, 2008 doi:10.1152/ajpregu.00147.2008This study compared the baroreflex control of lumbar and renal sympathetic nerve activity (SNA) in conscious rats. Arterial pressure (AP) and lumbar and renal SNA were simultaneously recorded in six freely behaving rats. Pharmacological estimates of lumbar and renal sympathetic baroreflex sensitivity (BRS) were obtained by means of the sequential intravenous administration of sodium nitroprusside and phenylephrine. Sympathetic BRS was significantly (P Ͻ 0.05) lower for lumbar [3.0 Ϯ 0.4 normalized units (NU)/mmHg] than for renal (7.6 Ϯ 0.6 NU/mmHg) SNA. During a 219-min baseline period, spontaneous lumbar and renal BRS were continuously assessed by computing the gain of the transfer function relating AP and SNA at heart rate frequency over consecutive 61.4-s periods. The transfer gain was considered only when coherence between AP and SNA significantly differed from zero, which was verified in 99 Ϯ 1 and 96 Ϯ 3% of cases for lumbar and renal SNA, respectively. When averaged over the entire baseline period, spontaneous BRS was significantly (P Ͻ 0.05) lower for lumbar (1.3 Ϯ 0.2 NU/mmHg) than for renal (2.3 Ϯ 0.3 NU/mmHg) SNA. For both SNAs, spontaneous BRS showed marked fluctuations (variation coefficients were 26 Ϯ 2 and 28 Ϯ 2% for lumbar and renal SNA, respectively). These fluctuations were positively correlated in five of six rats (R ϭ 0.44 Ϯ 0.06; n ϭ 204 Ϯ 8; P Ͻ 0.0001). We conclude that in conscious rats, the baroreflex control of lumbar and renal SNA shows quantitative differences but is modulated in a mostly coordinated way. arterial pressure; baroreceptor reflex; sympathetic nervous system; transfer function THE ARTERIAL BARORECEPTOR reflex plays a major role in the short-term control of arterial pressure (AP) mainly through the modulation of efferent sympathetic nerve activity (SNA) to regional circulations (12). In rats, studies aimed at characterizing the baroreflex control of SNA under physiological conditions, i.e., in the conscious state, have been based mostly on recordings of renal SNA (RSNA;3,5,7,10,13,16,20,23,25), mainly because of the purely postganglionic nature of this activity. Most often, authors implicitly assumed that RSNA provided a reliable reflection of other regional SNAs. In the meantime, evidence has accumulated suggesting a differential baroreflex control of regional SNAs in several animal species (22). In the rat, the comparison of the baroreflex control of regional SNAs has been carried out in urethane-chloralose anesthetized animals by using the vasoactive drug injection technique, i.e., the so-called pharmacological method (29,30). In these studies, it was reported that the characteristics of the baroreflex function curves differed between RSNA, lumbar SNA (LSNA), and adrenal SNA. In conscious rats, this information has not...

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