Baroreflex control of sympathetic outflow in pregnant rats: effects of captopril

1990 ◽  
Vol 258 (6) ◽  
pp. R1417-R1423 ◽  
Author(s):  
M. E. Crandall ◽  
C. M. Heesch
Keyword(s):  
Base Line ◽  
Operating Pressure ◽  
Sympathetic Outflow ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Pregnant Rats ◽  
Baroreflex Control ◽  
Renal Sympathetic Nerve Activity ◽  
Near Term ◽  
Renal Sympathetic

Arterial baroreflex control of renal sympathetic nerve activity (RSNA) was compared in nonpregnant (NP) and near-term pregnant (P) chloralose-anesthetized rats. Baroreflex curves were obtained by recording reflex changes in RSNA (expressed as a percent of base line) due to increases and decreases in mean arterial pressure (MAP) [intravenous phenylephrine and nitroprusside (NTP)]. The slope, midpoint (EP50), and threshold pressures of the baroreflex curves were compared. Base-line MAP was significantly lower in the pregnant animals (P = 96 +/- 3 vs. NP = 113 +/- 5 mmHg). The baroreflex curves of pregnant animals also had significantly lower threshold (P = 95 +/- 3 vs. NP = 110 +/- 5 mmHg) and midpoint values (P = 105 +/- 4 vs. NP = 119 +/- 5 mmHg). The response to unloading the baroreceptors was attenuated in the pregnant animals as indicated by a decrease in slope of the NTP portion of the baroreflex curve (P = 0.95 +/- 0.17 vs. NP = 1.61 +/- 0.29% nerve activity/mmHg). Responses to blockade of angiotensin-converting enzyme with captopril (2 mg/kg iv) were also examined. There were no differences in EP50 or slope among the control, captopril, and recovery baroreflex curves within either the nonpregnant or pregnant animals. However, after captopril, MAP decreased to a greater extent in the pregnant rats, yet RSNA increased to the same level for the two groups. Thus pregnancy results in a leftward shift of the baroreflex function curve toward a lower operating pressure range. In addition, pregnant rats demonstrated an impaired ability to increase sympathetic outflow above base-line values in response to a hypotensive challenge.

Effects of pregnancy and progesterone metabolites on arterial baroreflex in conscious rats

1997 ◽  
Vol 272 (3) ◽  
pp. R924-R934 ◽  
Author(s):  
S. Masilamani ◽  
C. M. Heesch
Keyword(s):  
Sympathetic Nerve Activity ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Renal Sympathetic Nerve Activity ◽  
Conscious Rats ◽  
Progesterone Metabolites ◽  
Progesterone Metabolite ◽  
In Pregnancy ◽  
Renal Sympathetic

Previous experiments in anesthetized rats suggested that sympathoexcitatory responses were attenuated in pregnant (P) rats. The major progesterone metabolite, 3alpha-hydroxy-dihydroprogesterone (3alpha-OH-DHP), is elevated in pregnancy and reportedly potentiates central gamma-aminobutyric acidergic mechanisms, whereas the 3beta-isomer (3beta-OH-DHP) is inactive. This study obtained baroreflex curves in conscious rats by recording reflex changes in renal sympathetic nerve activity (RSNA) and heart rate (HR) due to perturbations in mean arterial pressure (MAP) [i.v. phenylephrine (PE) and nitroprusside (NTP)] in P rats and in virgin (V) rats before (control) and 15 min after infusion (i.v.) of 3alpha-OH-DHP or 3beta-OH-DHP. Baseline MAP was lower in P rats (P = 102 +/- 2 vs. V = 124 +/- 3 mmHg). Compared with V rats, P rats exhibited less "sympathetic reserve" to respond to a hypotensive challenge, as evidenced by decreased maximum NA and decreased slope of RSNA baroreflex responses to NTP. However, HR baroreflex curves were similar in P and V rats. Acute intravenous administration of 3alpha-OH-DHP to conscious V rats mimicked the effects of pregnancy. Baroreflex sympathoexcitatory responses were decreased, whereas baroreflex control of HR was unaffected. The 3beta-isomer of DHP had no effect on NA or HR baroreflex responses. These results suggest that pregnancy may have differential effects on baroreflex control of sympathetic outflow and HR, and the major metabolite of progesterone, 3alpha-OH-DHP, may contribute to this adaptation of pregnancy.

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

2011 ◽  
Vol 96 (8) ◽  
pp. 736-744 ◽  
Author(s):  
Lindsea C. Booth ◽  
Alistair J. Gunn ◽  
Simon C. Malpas ◽  
Carolyn J. Barrett ◽  
Joanne O. Davidson ◽  
...  
Keyword(s):  
Heart Rate ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Fetal Sheep ◽  
Renal Sympathetic Nerve Activity ◽  
Renal Sympathetic Nerve ◽  
Near Term ◽  
Renal Sympathetic

Central mechanisms of acute ANG II modulation of arterial baroreflex control of renal sympathetic nerve activity

2002 ◽  
Vol 282 (5) ◽  
pp. H1592-H1602 ◽  
Author(s):  
Max G. Sanderford ◽  
Vernon S. Bishop
Keyword(s):  
Sympathetic Nerve ◽  
Intravenous Infusion ◽  
Sympathetic Nerve Activity ◽  
Ang Ii ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Renal Sympathetic Nerve Activity ◽  
Renal Sympathetic Nerve ◽  
Renal Sympathetic

Short-term intravenous infusion of angiotensin II (ANG II) into conscious rabbits reduces the range of renal sympathetic nerve activity (RSNA) by attenuating reflex disinhibition of RSNA. This action of ANG II to attenuate the arterial baroreflex range is exaggerated when ANG II is directed into the vertebral circulation, which suggests a mechanism involving the central nervous system. Because an intact area postrema (AP) is required for ANG II to attenuate arterial baroreflex-mediated bradycardia and is also required for maintenance of ANG II-dependent hypertension, we hypothesized that attenuation of maximum RSNA during infusion of ANG II involves the AP. In conscious AP-lesioned (APX) and AP-intact rabbits, we compared the effect of a 5-min intravenous infusion of ANG II (10 and 20 ng · kg−1 · min−1) on the relationship between mean arterial blood pressure (MAP) and RSNA. Intravenous infusion of ANG II into AP-intact rabbits resulted in a dose-related attenuation of maximum RSNA observed at low MAP. In contrast, ANG II had no effect on maximum RSNA in APX rabbits. To further localize the central site of ANG II action, its effect on the arterial baroreflex was assessed after a midcollicular decerebration. Decerebration did not alter arterial baroreflex control of RSNA compared with the control state, but as in APX, ANG II did not attenuate the maximum RSNA observed at low MAP. The results of this study indicate that central actions of peripheral ANG II to attenuate reflex disinhibition of RSNA not only involve the AP, but may also involve a neural interaction rostral to the level of decerebration.

Arterial baroreceptor reflex control of renal sympathetic nerve activity following chronic myocardial infarction in male, female, and ovariectomized female rats

2015 ◽  
Vol 309 (2) ◽  
pp. R169-R178 ◽  
Author(s):  
Maximilian I. Pinkham ◽  
Gillian A. Whalley ◽  
Sarah-Jane Guild ◽  
Simon C. Malpas ◽  
Carolyn J. Barrett
Keyword(s):  
Myocardial Infarction ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Sham Group ◽  
Chronic Myocardial Infarction ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Renal Sympathetic Nerve Activity ◽  
Renal Sympathetic

There is controversy regarding whether the arterial baroreflex control of renal sympathetic nerve activity (SNA) in heart failure is altered. We investigated the impact of sex and ovarian hormones on changes in the arterial baroreflex control of renal SNA following a chronic myocardial infarction (MI). Renal SNA and arterial pressure were recorded in chloralose-urethane anesthetized male, female, and ovariectomized female (OVX) Wistar rats 6–7 wk postsham or MI surgery. Animals were grouped according to MI size (sham, small and large MI). Ovary-intact females had a lower mortality rate post-MI (24%) compared with both males (38%) and OVX (50%) ( P < 0.05). Males and OVX with large MI, but not small MI, displayed an impaired ability of the arterial baroreflex to inhibit renal SNA. As a result, the male large MI group (49 ± 6 vs. 84 ± 5% in male sham group) and OVX large MI group (37 ± 3 vs. 75 ± 5% in OVX sham group) displayed significantly reduced arterial baroreflex range of control of normalized renal SNA ( P < 0.05). In ovary-intact females, arterial baroreflex control of normalized renal SNA was unchanged regardless of MI size. In males and OVX there was a significant, positive correlation between left ventricle (LV) ejection fraction and arterial baroreflex range of control of normalized renal SNA, but not absolute renal SNA, that was not evident in ovary-intact females. The current findings demonstrate that the arterial baroreflex control of renal SNA post-MI is preserved in ovary-intact females, and the state of left ventricular dysfunction significantly impacts on the changes in the arterial baroreflex post-MI.

Increase in sympathetic activity with age. I. Role of impairment of arterial baroreflexes

1991 ◽  
Vol 260 (4) ◽  
pp. H1113-H1120 ◽  
Author(s):  
G. Hajduczok ◽  
M. W. Chapleau ◽  
S. L. Johnson ◽  
F. M. Abboud
Keyword(s):  
Sympathetic Nerve Activity ◽  
Carotid Sinus ◽  
Conscious State ◽  
Bolus Administration ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Renal Sympathetic Nerve Activity ◽  
Renal Sympathetic

The purpose of this study was to evaluate changes in arterial baroreflex function with aging. Mean arterial pressure (MAP) obtained in the awake state was 110 +/- 7 mmHg in the young animals (1 yr; n = 5) and 128 +/- 6 mmHg in the old beagles (11 yr; n = 11) (P less than 0.05). In response to bolus administration of varying doses of phenylephrine and nitroglycerin in the conscious state, the slope relating heart rate (HR) to MAP was attenuated significantly in the old animals compared with the young (-0.87 +/- 0.30 vs. -2.35 +/- 0.44 beats.min-1.mmHg-1; P less than 0.05). After atropine, the baroreflex control of HR was abolished in both groups. After anesthesia and sectioning of the aortic depressor nerves, and with isolated carotid sinus pressures (CSP) held at 50 mmHg, absolute renal sympathetic nerve activity (RSNA) was significantly greater in the old (368 +/- 40 Hz) vs. the young animals (41 +/- 9 Hz). In the old, the gains of baroreflex inhibition of MAP (0.78 +/- 0.09) and normalized RSNA (0.38 +/- 0.14%/mmHg) during increases in CSP were decreased significantly compared with the young (MAP, 1.16 +/- 0.17 mmHg, and RSNA, 0.72 +/- 0.06%/mmHg). In a subgroup of old normotensive animals (n = 5), the baroreflex gain of RSNA was still attenuated (0.43 +/- 0.11%/mmHg) compared with the young. The reflex reduction in absolute RSNA as a function of baseline RSNA was also impaired in old vs. young beagles.(ABSTRACT TRUNCATED AT 250 WORDS)

Arterial baroreflex during pregnancy and renal sympathetic nerve activity during parturition in rabbits

1998 ◽  
Vol 274 (5) ◽  
pp. H1635-H1642 ◽  
Author(s):  
Kathleen P. O’Hagan ◽  
Susan M. Casey
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Renal Sympathetic Nerve Activity ◽  
Renal Sympathetic Nerve ◽  
Reflex Gain ◽  
Maximal Gain ◽  
Renal Sympathetic

The arterial baroreflex control of renal sympathetic nerve activity (RSNA) was evaluated in nine term pregnant (P) and 12 nonpregnant (NP) conscious New Zealand White rabbits. In an additional four P rabbits, the RSNA response to spontaneous parturition was measured. The blood pressure (BP)-RSNA relationship was generated by sequential inflations of aortic and vena caval perivascular occluders. Rest BP (P: 61 ± 2 vs. NP: 73 ± 2 mmHg) and the centering point of the baroreflex (P: 57 ± 2 vs. NP: 70 ± 2 mmHg) were lower ( P < 0.05) in term pregnancy. Baroreflex range (P: 246 ± 14% vs. NP 263 ± 24% of rest RSNA) was not affected by pregnancy. However, maximal reflex gain was moderately depressed (−44%) in P rabbits (P: −15 ± 1 vs. NP: −27 ± 4% of rest RSNA/mmHg; P < 0.05) due to a significant reduction in the slope coefficient. Delivery of a fetus was associated with strong renal sympathoexcitation. Peak RSNA averaged 80 ± 37% of smoke-elicited RSNA or 1,221 ± 288% of rest RSNA (mean ± SD). These results suggest that, in contrast to rat pregnancy, depressed arterial baroreflex control of RSNA in rabbit pregnancy is due primarily to a reduction in maximal gain rather than a reduction in the maximal sympathetic response to hypotension.

Gestational effects on volume-sensitive cardiopulmonary receptor reflexes in the rat

1995 ◽  
Vol 268 (3) ◽  
pp. R736-R743 ◽  
Author(s):  
T. Hines ◽  
S. W. Mifflin
Keyword(s):  
Sympathetic Nerve Activity ◽  
Right Atrial ◽  
Nerve Activity ◽  
Pregnant Rats ◽  
Renal Sympathetic Nerve Activity ◽  
Cell Discharge ◽  
Afferent Stimulus ◽  
Gallamine Triethiodide ◽  
Renal Sympathetic ◽  
Stimulation Of

We tested the hypothesis that augmented reflex sympathoinhibition mediated by volume-sensitive cardiopulmonary (CP) receptors contributes to the vasodilation of pregnancy by comparing responses to acute volume expansion in 21-day-pregnant and age-matched virgin rats (n = 7) that were anesthetized (pentobarbital sodium, 50 mg/kg ip), paralyzed (gallamine triethiodide, 25 mg/kg iv), ventilated, and had undergone bilateral sinoaortic denervation. CP receptors were stimulated with intra-atrial injections of saline (50, 100, 200, and 300 microliter), and the following variables were recorded: 1) mean right atrial pressure (MRAP) to index the afferent stimulus intensity; 2) cell discharge in the nucleus tractus solitarii (NTS), the primary central terminus for CP afferents; and 3) mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) to assess efferent reflex effects. Basal MAP was significantly lower in pregnant (71.5 +/- 3.8 mmHg) than in virgin rats (86.6 +/- 3.1 mmHg), and plasma volume was expanded in the pregnant group (17.6 +/- 1.1 vs. 10.0 +/- 0.7 ml, P < 0.05). Baseline MRAP was similar between groups. Saline injections evoked graded increases in MRAP, which were larger in gravid animals (P < 0.05). Volume injections evoked similar changes in NTS cell discharge between groups, but the responses were nongraded. Despite larger changes in MRAP in gravid rats, reflex effects on RSNA and HR were similar to those in control animals, and effects on MAP were attenuated in the pregnant group. We conclude that larger changes in MRAP in pregnant rats during stimulation of CP receptors are not associated with larger changes in central or efferent components of this reflex.(ABSTRACT TRUNCATED AT 250 WORDS)

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