Arterial baroreflex resetting mediates postexercise reductions in arterial pressure and heart rate

1998 ◽  
Vol 275 (5) ◽  
pp. H1627-H1634 ◽  
Author(s):  
Margaret P. Chandler ◽  
David W. Rodenbaugh ◽  
Stephen E. DiCarlo
Keyword(s):  
Heart Rate ◽  
Arterial Pressure ◽  
Acute Exercise ◽  
Operating Point ◽  
Arterial Baroreflex ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Single Bout ◽  
Before And After ◽  
The Relationship

We tested the hypothesis that postexercise reductions in arterial pressure and heart rate (HR) are mediated by a lowering of the operating point and a reduction in the gain of the arterial baroreflex. To test this hypothesis, spontaneous changes in arterial pressure and the reflex responses of HR were examined before and after a single bout of mild to moderate dynamic exercise in 19 spontaneously hypertensive rats (SHR, 10 male and 9 female). Eleven SHR subjected to sinoaortic denervation (SAD) (6 male, 5 female) were also studied. All rats were instrumented with an arterial catheter for the measurement of arterial pressure and HR. After exercise, arterial pressure and HR were reduced below preexercise levels. Furthermore, the operating point and spontaneous gain (G) of the arterial baroreflex were reduced. Specifically, after exercise, the spontaneous range of HR (P1, 50%), the pressure at the midpoint of the pressure range (P3, 13%) and the HR at the midpoint of the HR range (H3, 10%), the spontaneous minimum HR (P4, 8%) and maximum HR (10%), and G (76%) were significantly attenuated. SAD significantly attenuated the relationship between arterial pressure and HR by reducing G (males 94%, females 95%). These results demonstrate that acute exercise resulted in a postexercise resetting of the operating point and a reduction in the gain of the arterial baroreflex. Furthermore, these data suggest that postexercise reductions in arterial pressure and HR are mediated by a lowering of the operating point of the arterial baroreflex.

Sinoaortic denervation prevents postexercise reductions in arterial pressure and cardiac sympathetic tonus

1997 ◽  
Vol 273 (6) ◽  
pp. H2738-H2745 ◽  
Author(s):  
Margaret P. Chandler ◽  
Stephen E. Dicarlo
Keyword(s):  
Heart Rate ◽  
Arterial Pressure ◽  
Spontaneously Hypertensive Rats ◽  
Acute Exercise ◽  
Dynamic Exercise ◽  
Arterial Baroreflex ◽  
Hypertensive Rats ◽  
Experimental Conditions ◽  
Spontaneously Hypertensive ◽  
Single Bout

Arterial pressure, cardiac sympathetic tonus (ST), and heart rate (HR) are reduced after a single bout of dynamic exercise in spontaneously hypertensive rats (SHR). To test if the arterial baroreflex is required for these postexercise responses, intact ( n = 9) and sinoaortic-denervated (SAD) rats ( n = 5) were chronically instrumented with an arterial catheter for the measurement of arterial pressure and HR and for the infusion of cardiac autonomic antagonists. Five days after instrumentation, cardiac ST and parasympathetic tonus (PT) were determined under two experimental conditions (no exercise and postexercise). SAD rats did not alter no-exercise cardiac ST (intact 47 ± 3 vs. SAD 50 ± 3 beats/min); however, no-exercise PT was reduced (intact −24 ± 2 vs. SAD −4 ± 4 beats/min, P < 0.05). Acute exercise reduced arterial pressure (postexertional hypotension, −20 ± 3 mmHg, P < 0.05), cardiac ST (no exercise 47 ± 3 vs. postexercise 24 ± 3 beats/min, P < 0.05), and PT (no exercise −24 ± 2 vs. postexercise −11 ± 2 beats/min, P < 0.05) in intact SHR. In contrast, SAD prevented postexercise reductions in arterial pressure and cardiac ST (no exercise 50 ± 3 vs. postexercise 59 ± 7 beats/min). Furthermore, SAD had no effect on postexercise PT (no exercise −4 ± 4 vs. postexercise −7 ± 4 beats/min). These results demonstrate that the arterial baroreflex is required for the reduction in arterial pressure and cardiac ST that occurs in SHR after a single bout of dynamic exercise.

Dynamic exercise shifts the operating point and reduces the gain of the arterial baroreflex in rats

1998 ◽  
Vol 275 (6) ◽  
pp. R2043-R2048 ◽  
Author(s):  
Heather R. Burger ◽  
Margaret P. Chandler ◽  
David W. Rodenbaugh ◽  
Stephen E. DiCarlo
Keyword(s):  
Pressure Range ◽  
Dynamic Exercise ◽  
Treadmill Running ◽  
Operating Point ◽  
Arterial Baroreflex ◽  
Hypertensive Rats ◽  
Baroreflex Control ◽  
Spontaneously Hypertensive ◽  
The Relationship ◽  
Carotid Arterial

We tested the hypothesis that dynamic exercise resets the operating point and attenuates the gain of the arterial baroreflex regulation of heart rate (HR) in rats. Seven adult female spontaneously hypertensive rats (SHR) were chronically instrumented with left carotid arterial catheters. After the rats recovered, arterial baroreflex function was examined by recording reflex changes in HR in response to spontaneous changes in arterial pressure (AP) during a preexercise condition and during steady-state treadmill running at 6 and 18 m/min. Dynamic exercise at 6 and 18 m/min, respectively, reduced the spontaneous range (by 55 and 70%) and spontaneous gain (by 64 and 82%) of the arterial baroreflex control of HR. Dynamic exercise at 6 and 18 m/min, respectively, also increased the pressure at the midpoint of the spontaneous pressure range (by 7 and 12%), the spontaneous minimum HR response (by 35 and 59%), the HR at the midpoint of the spontaneous HR range (by 31 and 52%), and the spontaneous maximum HR response (by 27 and 46%). Sinoaortic denervation eliminated the relationship between AP and HR by reducing the spontaneous gain 95%. These results demonstrate that dynamic exercise shifted the operating point of the arterial baroreflex to a higher pressure and reduced the spontaneous gain in female SHR.

Exercise Training Improves the Depressed Sensitivity of the Baroreceptors in Spontaneously Hypertensive Rats

Hypertension ◽  
2000 ◽  
Vol 36 (suppl_1) ◽  
pp. 700-701
Author(s):  
Gustavo J J Silva ◽  
Edson D Moreira ◽  
Carlos E Negrao ◽  
Patricia C Brum ◽  
Eduardo M Krieger
Keyword(s):  
Blood Pressure ◽  
Arterial Pressure ◽  
Spontaneously Hypertensive Rats ◽  
Systolic Arterial Pressure ◽  
Arterial Baroreflex ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Baroreceptor Function ◽  
Low Intensity Exercise ◽  
The Relationship

P43 We have previously demonstrated that low-intensity exercise traning (ET) diminishes blood pressure and partially restores the sensitivity of the baroreflex bradycardia and tachycardia that are depressed in spontaneously hypertensive rats (SHR). Presently, the influence of the exercise trainig (ET) on the afferent part of the baroreflex (baroreceptor function curve) and its implication on the baroreflex was analysed in SHR and in normal control rats (NCR). NCR and SHR were subdivided in sedentary (S) and ET groups: SHR-S (n=8) and SHR-ET (n=6), and NCR-S (n=8) and NCR-ET (n=8). ET was performed on treadmill, during 60 min, 5 days/wk, at 50% of VO 2 max, for 12 wk. Arterial baroreflex sensitivity was evaluated by bradycardiac responses to phenylephrine (0.5;1;2;4;8 and 16 μg/ml, i.v.) and tachycardiac responses to sodium nitroprusside (0.5;1;2;4;8 and 16 μg/ml, i.v.). Aortic baroreceptor function curve was evaluated under pentobarbital anesthesia (40 mg/kg) during rapid variations of arterial pressure (AT/CODAS, 3kHz per channel). The relationship between changes in baroreceptor discharge (0-100%) and systolic arterial pressure was analysed using a sigmoidal regression. Mean arterial pressure was reduced in SHR-ET compared to SHR-S group (165±7 vs. 183±4 mmHg) but remained inaltared in NCR-ET compared to NCR-S (112±3 vs. 115±3 mmHg). In SHR, ET increased the sensitivity of baroreflex bradycardia (1.9±0.1 vs. 0.7±0.1 bpm.mmHg -1 ) and tachycardia (2.9±0.1 vs. 1.8±0.2 bpm.mmHg -1 ) which were depressed. In NCR-ET baroreflex bradycardia was decreased (1.4±0.1 vs. 1.7±0.1 bpm.mmHg -1 ) but baroreflex tachycardia was increased (4.6±0.5 vs. 3.0±0.2 bpm.mmHg -1 ). ET increased the aortic baroreceptor gaing-sensitivity in both groups: SHR (0.9±0.1 vs. 0.7±0.1 %.mmHg -1 ) and NCR (2.1±0.1 vs. 1.4±0.1 %.mm Hg -1 ). Conclusion:1. ET increases aortic baroreceptor gain-sensitivity in NCR as well in SHR; 2. The improvement of the baroreflex produced by ET in SHR is partially explainedd by the recovery of the baroreceptor sensitivity, which may also participate in the reduction of high blood pressure.

Arterial baroreflex regulation of regional vascular conductance at rest and during exercise

2000 ◽  
Vol 278 (6) ◽  
pp. R1634-R1642 ◽  
Author(s):  
Brenda Martínez-Nieves ◽  
Heidi L. Collins ◽  
Stephen E. DiCarlo
Keyword(s):  
Mean Arterial Pressure ◽  
Arterial Pressure ◽  
Dynamic Exercise ◽  
Treadmill Running ◽  
Arterial Baroreflex ◽  
Hypertensive Rats ◽  
Vascular Conductance ◽  
Spontaneously Hypertensive ◽  
Spontaneous Baroreflex ◽  
The Relationship

We tested the hypothesis that dynamic exercise resets the operating point and attenuates the spontaneous gain of the arterial baroreflex regulation of mesenteric and hindlimb vascular conductance in hypertensive rats. Eleven adult male spontaneously hypertensive rats were chronically instrumented with left carotid arterial catheters and Doppler ultrasonic flow probes around the superior mesenteric and left common iliac arteries. After the rats recovered, arterial baroreflex function was examined by recording reflex changes in conductance in response to spontaneous changes in mean arterial pressure before exercise and during steady-state treadmill running at 6 and 18 m/min. Dynamic exercise reduced the spontaneous baroreflex gain of mesenteric conductance (by 51 and 36%) and maximum mesenteric conductance (by 24 and 32%) at 6 and 18 m/min, respectively. In sharp contrast, dynamic exercise increased the spontaneous maximum iliac conductance (by 32 and 47%) without changing the spontaneous gain. Sinoaortic denervation eliminated the relationship between mean arterial pressure and conductance by reducing the mesenteric (92%) and iliac (68%) vascular conductance gain. These results demonstrate that dynamic exercise has differential effects on the regulation of mesenteric and iliac vascular conductance in hypertensive rats.

Regression of myocardial hypertrophy and influence of adrenergic system

1983 ◽  
Vol 244 (1) ◽  
pp. H97-H101 ◽  
Author(s):  
S. Sen ◽  
R. C. Tarazi
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Regression Analysis ◽  
Arterial Pressure ◽  
Spontaneously Hypertensive Rats ◽  
Myocardial Hypertrophy ◽  
Cardiac Response ◽  
Adrenergic System ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive

Studies of regression of myocardial hypertrophy in spontaneously hypertensive rats (SHR) suggest that the adrenergic system may play an important role in the reversal of hypertrophy. The effect of propranolol on reversal of hypertrophy, however, is still controversial. This study describes the effect of propranolol, given alone or in combination with hydralazine in different ratios for 4 wk, on blood pressure (BP), ventricular weight, and myocardial catecholamine (MC) concentrations. The data show that a certain ratio of propranolol to hydralazine (750:30) leads to moderate BP control (196-156 mmHg) without increased MC (634 vs. 552 ng/g) and moderately reduced hypertrophy. Reduction of BP alone with increased MC (hydralazine alone) or reduction of MC without BP control (propranolol alone) failed to reduce hypertrophy. A significant correlation between both ventricular weight and heart rate with MC (r = 0.6) was obtained by multiple regression analysis. This study suggests that adrenergic factors seem to play an important role in modulating structural cardiac response to variations in arterial pressure.

Clonidine fails to reduce pressor responsiveness of conscious spontaneously hypertensive rats to vasopressin

1986 ◽  
Vol 64 (3) ◽  
pp. 284-289 ◽  
Author(s):  
Sunil Datar ◽  
William H. Laverty ◽  
J. Robert McNeill
Keyword(s):  
Heart Rate ◽  
Arterial Pressure ◽  
Spontaneously Hypertensive Rats ◽  
Reflex Activity ◽  
Unexpected Finding ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Wky Rats ◽  
Wistar Kyoto ◽  
Shr And Wky Rats

Pressor responses and heart rate responses to intravenous injections (3.5–50.0 pmol/kg) of arginine vasopressin (AVP) were recorded in saline- and clonidine-treated spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Clonidine (20 μg/kg, i. v.) caused a marked fall of arterial pressure in SHR but not in WKY rats so that, 20 min after the injection of the α2-adrenoceptor agonist, arterial pressure was similar in the two strains of rats. The curve expressing the relationship between the dose of AVP and the increase of arterial pressure for saline-treated SHR was positioned to the left of that for saline-treated WKY rats. This enhanced pressor responsiveness of SHR to AVP may have been related to impaired reflex activity since heart rate fell much less in SHR than in WKY rats for a given elevation in pressure. Pressure responses to AVP were augmented by clonidine in both SHR and WKY rats so that, similar to saline-treated rats, pressor responsiveness to the peptide was still greater in SHR. Heart rate responses to AVP were not altered significantly by clonidine. The results indicate that clonidine fails to enhance reflex activity and reduce pressor responsiveness of SHR to AVP. The increased pressor responsiveness of both SHR and WKY rats to AVP following clonidine was an unexpected finding and may be related to a peripheral interaction between α-adrenergic agonists and AVP.

Acute exercise and gender alter cardiac autonomic tonus differently in hypertensive and normotensive rats

1998 ◽  
Vol 274 (2) ◽  
pp. R510-R516 ◽  
Author(s):  
Margaret P. Chandler ◽  
Stephen E. Dicarlo
Keyword(s):  
Spontaneously Hypertensive Rats ◽  
Acute Exercise ◽  
Female Rats ◽  
Male Rats ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Cardiac Autonomic Regulation ◽  
Before And After ◽  
Wistar Kyoto ◽  
And Gender

Arterial pressure (AP), heart rate (HR), cardiac sympathetic tonus (ST), and parasympathetic tonus (PT) were determined in spontaneously hypertensive rats (SHR, 8 male and 8 female) and Wistar-Kyoto normotensive rats (WKY, 8 male and 12 female) before and after acute exercise. Before exercise, hypertensive rats (regardless of gender) had an increased ST (+15 beats/min), increased resting HR (+12 beats/min), and decreased PT (−11 beats/min). Similarly, female rats (regardless of strain) also had an increased ST (+15 beats/min), increased resting HR (+39 beats/min), and decreased PT (−14 beats/min). Hypertensive rats had a significant reduction in AP (−17 ± 3 mmHg), ST (−26 beats/min), PT (−7 beats/min), and HR (−14 beats/min) after exercise. In contrast, AP was not reduced in normotensive rats and ST (+18 beats/min) and HR (+42 beats/min) were increased in female normotensive rats after exercise. However, male normotensive rats had a postexercise reduction in ST (−14 beats/min) and HR (−19 beats/min). In summary, AP, ST, and resting HR were higher whereas PT was lower in hypertensive vs. normotensive rats. Furthermore, females had a higher resting HR, intrinsic HR, and ST and lower PT than male rats. These data demonstrate that gender and the resting level of AP influence cardiac autonomic regulation.

scholarly journals Heart rate and arterial pressure variability and baroreflex sensitivity in ovariectomized spontaneously hypertensive rats

Life Sciences ◽  
2009 ◽  
Vol 84 (21-22) ◽  
pp. 719-724 ◽  
Author(s):  
Valdo José Dias da Silva ◽  
Rodrigo Miranda ◽  
Luciano Oliveira ◽  
Carlos Henrique F. Rodrigues Alves ◽  
Glaucia Helana Fortes Van Gils ◽  
...  
Keyword(s):  
Heart Rate ◽  
Arterial Pressure ◽  
Spontaneously Hypertensive Rats ◽  
Baroreflex Sensitivity ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Arterial Pressure Variability

Kappa opioids modulate the arterial baroreflex control of heart rate in conscious young sheep

2007 ◽  
Vol 85 (8) ◽  
pp. 811-817 ◽  
Author(s):  
Wei Qi ◽  
Francine G. Smith
Keyword(s):  
Heart Rate ◽  
Arterial Pressure ◽  
Direct Evidence ◽  
Opiate Receptors ◽  
Random Order ◽  
Arterial Baroreflex ◽  
Baroreflex Control ◽  
Physiological Conditions ◽  
Kappa Opioids ◽  
Before And After

The present study tested the hypothesis that κ-opioids modulate the arterial baroreflex control of heart rate in conscious young sheep. Various parameters governing the arterial baroreflex control of heart rate were assessed before and after activation of κ-opiate receptors (KOR) by i.v. administration of the specific KOR agonist U-50488H (experiment 1) or vehicle (experiment 2) to conscious, chronically instrumented lambs aged 42 ± 2 days (n = 6). The 2 experiments were administered in random order at minimum intervals of 48 h. Thirty min after U-50488H treatment, there was an increase in diastolic and mean arterial pressure and in heart rate, returning to control levels by 90 min. A significant increase in the arterial pressure at the midpoint of the baroreflex range and in the minimum heart rate as well as a significant decrease in the heart rate range over which the arterial baroreflex operates were also seen at 30 min after U-50488H, gradually returning to control levels over 120 min. Vehicle had no effect on any of the parameters governing the arterial baroreflex control of heart rate. These data provide the first direct evidence that under physiological conditions in young lambs, the arterial baroreflex control of heart rate is altered after administration of the specific KOR agonist U-50488H, revealing a previously unidentified role for this opioid receptor.

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