Baroreflex control of renal sympathetic nerve activity and heart rate in near-term fetal sheep

Heart rate (HR) and renal sympathetic nerve activity (RSNA) responses to ramp changes in blood pressure (BP) by (de)pressor agents and to acute volume expansion were recorded in conscious young, mature, and old Wistar rats maintained for 4 wk on diets containing low, control, or high dietary Na. Both HR and RSNA responses to BP increases or decreases were attenuated on low-Na diet compared with control Na diet. On high-Na diet, HR responses to BP changes and RSNA responses to BP increases were also attenuated, but in contrast the excitatory response of RSNA to BP decreases was augmented. The inhibitory RSNA response, but not the HR response, to volume expansion was significantly attenuated in young rats on high-Na diet but not on low-Na diet. The effects of both low and high dietary Na on HR and RSNA responses were most marked in young rats, less in mature rats, and even less in old rats. These results indicate a discordance of high dietary Na-induced changes in HR vs. RSNA control by the arterial and cardiopulmonary baroreflex, which is suggestive of central mechanisms affected by dietary Na. The developing nervous system appears to be the most responsive to dietary Na.

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Baroreflex control of heart rate and renal sympathetic nerve activity in rats with low brain angiotensinogen

Neuropeptides ◽

10.1016/j.npep.2007.12.003 ◽

2008 ◽

Vol 42 (2) ◽

pp. 159-168 ◽

Cited By ~ 11

Author(s):

Sordaini M. Caligiorne ◽

Ana Quênia G. Silva ◽

Marco A.P. Fontes ◽

Jose R. Silva ◽

Ovidiu Baltatu ◽

...

Keyword(s):

Heart Rate ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Nerve Activity ◽

Baroreflex Control ◽

Renal Sympathetic Nerve Activity ◽

Renal Sympathetic Nerve ◽

Renal Sympathetic

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Renal sympathetic nerve activity during asphyxia in fetal sheep

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00063.2012 ◽

2012 ◽

Vol 303 (1) ◽

pp. R30-R38 ◽

Cited By ~ 15

Author(s):

Lindsea C. Booth ◽

Simon C. Malpas ◽

Carolyn J. Barrett ◽

Sarah-Jane Guild ◽

Alistair J. Gunn ◽

...

Keyword(s):

Blood Pressure ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Nerve Activity ◽

Fetal Sheep ◽

Renal Sympathetic Nerve Activity ◽

Renal Sympathetic Nerve ◽

Arterial Blood ◽

Near Term ◽

Renal Sympathetic

The sympathetic nervous system (SNS) is an important mediator of fetal adaptation to life-threatening in utero challenges, such as asphyxia. Although the SNS is active well before term, SNS responses mature significantly over the last third of gestation, and its functional contribution to adaptation to asphyxia over this critical period of life remains unclear. Therefore, we examined the hypotheses that increased renal sympathetic nerve activity (RSNA) is the primary mediator of decreased renal vascular conductance (RVC) during complete umbilical cord occlusion in preterm fetal sheep (101 ± 1 days; term 147 days) and that near-term fetuses (119 ± 0 days) would have a more rapid initial vasomotor response, with a greater increase in RSNA. Causality of the relationship of RSNA and RVC was investigated using surgical (preterm) and chemical (near-term) denervation. All fetal sheep showed a significant increase in RSNA with occlusion, which was more sustained but not significantly greater near-term. The initial fall in RVC was more rapid in near-term than preterm fetal sheep and preceded the large increase in RSNA. These data suggest that although RSNA can increase as early as 0.7 gestation, it is not the primary determinant of RVC. This finding was supported by denervation studies. Interestingly, chemical denervation in near-term fetal sheep was associated with an initial fall in blood pressure, suggesting that by 0.8 gestation sympathetic innervation of nonrenal vascular beds is critical to maintain arterial blood pressure during the rapid initial adaptation to asphyxia.

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Cardiovascular and neurohormonal effects of intravenous adrenomedullin in conscious rabbits

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1995.269.5.r1289 ◽

1995 ◽

Vol 269 (5) ◽

pp. R1289-R1293 ◽

Cited By ~ 11

Author(s):

M. Fukuhara ◽

T. Tsuchihashi ◽

I. Abe ◽

M. Fujishima

Keyword(s):

Heart Rate ◽

Mean Arterial Pressure ◽

Arterial Pressure ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Nerve Activity ◽

Renal Sympathetic Nerve Activity ◽

Renal Sympathetic Nerve ◽

Conscious Rabbits ◽

Renal Sympathetic

Adrenomedullin is a vasodilative peptide and shows slight homology with calcitonin gene-related peptide. In the present study, we investigated the effects of adrenomedullin on cardiovascular and neurohormonal responses in 13 conscious rabbits. The animals were chronically instrumented with bipolar electrodes on the left renal sympathetic nerve. Intravenous administration of human adrenomedullin (10, 100, 1,000, and 3,000 pmol/kg, n = 6) caused a dose-dependent reduction in mean arterial pressure (0 +/- 2, -1 +/- 2, -19 +/- 2, and -29 +/- 4 mmHg, respectively) concomitant with increases in heart rate, renal sympathetic nerve activity, plasma renin activity, and plasma norepinephrine. The significant reduction in mean arterial pressure induced by 1,000 pmol/kg of adrenomedullin occurred within 1 min after injection and lasted for 15 min (n = 7). In contrast, the significant increases in heart rate and renal sympathetic nerve activity lasted for more than 50 min. When mean arterial pressure was decreased by 15 mmHg by adrenomedullin, the increases in heart rate and renal sympathetic nerve activity were 53 +/- 8 beats/min and 78 +/- 13%, respectively, which were significantly smaller than those induced by intravenous injection of sodium nitroprusside (102 +/- 14 beats/min and 155 +/- 34%, respectively). These results suggest that intravenous adrenomedullin exerts a hypotensive action that is associated with the attenuated reflex-mediated sympathetic activation.

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Novel recordings of renal sympathetic nerve activity in conscious fetal sheep and newborn lambs

AJP Renal Physiology ◽

10.1152/ajprenal.1990.258.1.f218 ◽

1990 ◽

Vol 258 (1) ◽

pp. F218-F221 ◽

Cited By ~ 6

Author(s):

F. G. Smith ◽

J. M. Klinkefus ◽

U. C. Kopp ◽

J. E. Robillard

Keyword(s):

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Perinatal Period ◽

Postnatal Period ◽

Left Renal Artery ◽

Nerve Activity ◽

Fetal Sheep ◽

Renal Sympathetic Nerve Activity ◽

Renal Sympathetic Nerve ◽

Renal Sympathetic

This study describes a technique for measuring efferent renal sympathetic nerve activity (RSNA) during the perinatal period. Experiments were carried out in four chronically instrumented fetal sheep (gestational age, 134–140 days) and 6 newborn lambs (postnatal age, 3–7 days). Surgery, performed under halothane anesthesia, consisted of routine catheter insertions and placement of a Doppler flow probe around the left renal artery. In addition, bipolar platinum electrodes were placed on a branch of the left renal postganglionic nerve. At least 24 h after surgery RSNA was measured in conscious fetal and newborn animals. RSNA was pulse synchronous, reduced with pressor agents, and completely inhibited during ganglionic blockade. Using this method, we have provided direct evidence of efferent renal sympathetic nerve traffic in utero and in the immediate postnatal period. This technique opens new avenues into the investigation of the role of the sympathetic nervous system during the perinatal period.

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