Arterial Baroreflex Control of Cardiac Vagal Outflow in Older Individuals Can Be Enhanced by Aerobic Exercise Training

Deley, Gaëlle; Picard, Glen; Taylor, J. Andrew

doi:10.1161/hypertensionaha.109.130039

Cited by 48 publications

(74 citation statements)

References 61 publications

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“…6 The data is relevant since baroceptor reflex is largely studied in different models and strains of rats aiming to prevent hypertension development in humans 12,27-29 , because reduced baroreflex function is indicative of cardiovascular disease. [30][31][32][33] In conclusion, we found differences of baroreflex function among WKY rats. The majority of animals (82%) presented attenuated parasympathetic activity of the baroreflex (reduced bradycardic responses to increase in arterial pressure and reduced baroreflex gain tested with PE) while 22% presented decreased sympathetic activity of the baroreflex (reduced tachycardic responses to decreased arterial pressure and reduced baroreflex gain tested with SNP).…”

Section: Discussionmentioning

confidence: 94%

Intra-strain variations of baroreflex sensitivity in young Wistar-Kyoto rats

Valenti

Imaizumi²,

Abreu³

et al. 2009

CIM

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Clin Invest Med 2009; 32 (6): E251-E257. AbstractPurpose: To compare baroreflex sensitivity among conscious rats of the same strain. Methods: Male WKY rats (eight weeks old) were studied. Cannulas were inserted into the abdominal aortic artery through the right femoral artery to measure mean arterial pressure (MAP) and heart rate (HR). Baroreflex gain was calculated as the ratio between variation of HR in function of the MAP variation (ΔHR/ΔMAP) tested with a depressor dose of sodium nitroprusside (SNP, 50µg/kg, iv) and with a pressor dose of phenylephrine (PE, 8µg/kg, iv). We divided the rats into four groups: 1) Low bradycardic baroreflex (LB), BG between -1 and -2 bpm/mmHg tested with PE; 2) High bradycardic baroreflex (HB), BG < -2 bpm/mmHg tested with PE; 3) Low tachycardic baroreflex (LT), BG between -1 and -2 bpm/mmHg tested with SNP and; 4) High tachycardic baroreflex (HT), BG < -2 bpm/ mmHg tested with SNP. Significant differences were considered for p<0.05.Results: Approximately 82% of the rats presented reduced bradycardic reflex while 22 showed attenuated tachycardic reflex. No alterations were noted regarding basal MAP and HR, tachycardic and bradycardic peak and HR range. Conclusions: There was alteration in baroreflex sensitivity among rats of the same strain. Care should be taken when interpreting studies employing WKY as a control for the SHR.In 1963, Okamoto and Aoki 1 reported that they had selectively bred Wistar rats to be spontaneously hypertensive. Established as an inbred strain in 1969 at the National Institutes of Health (NIH), the spontaneously hypertensive rat (SHR) remains the most widely studied animal model of essential hypertension (i.e., persistent high blood pressure of unknown causation), and the strain presents similar characteristic to hypertension in humans. As controls for the SHR, most workers have employed normotensive descendants of Wistar rats that NIH investigators obtained in 1971 from the colony in Kyoto from which the SHR strain was originally derived (Wistar-Kyoto rats, WKY). 2 Baroreflex function is one of the body's homeostatic mechanisms to sustain arterial pressure. It offers a negative feedback loop in which the increased arterial pressure reflexively causes blood pressure to de-

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Section: Discussionmentioning

confidence: 94%

Intra-strain variations of baroreflex sensitivity in young Wistar-Kyoto rats

Valenti

Imaizumi²,

Abreu³

et al. 2009

CIM

View full text Add to dashboard Cite

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“…Whereas baseline AP is unaltered after training, the controlling mechanisms are changed. There is evidence supporting the increase in baroreflex gain in trained subjects (6,7,(9)(10)(11)23,29). Exercise training of normotensive male rats enhanced hypotension-induced tachycardia, whereas the bradycardic response was decreased or unchanged (7,23).…”

Section: Discussionmentioning

confidence: 97%

“…In contrast, resting bradycardia in young trained male rats has been more closely associated with alterations in cardiac pacemakers (4,5). Moreover, improvement in baroreflex control of HR observed in trained male animals (6)(7)(8) and humans (9)(10)(11) may also play a role in basal HR changes. Additionally, few studies have so far analyzed the effects of exercise training on cardiopulmonary reflex, which plays a role in the homeostasis of fluid balance.…”

Section: Introductionmentioning

confidence: 98%

Tonic and reflex cardiovascular autonomic control in trained-female rats

Sanches

Sartori

Jorge

et al. 2009

Braz J Med Biol Res

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The effects of exercise training on cardiovascular and autonomic functions were investigated in female rats. After an aerobic exercise training period (treadmill: 5 days/week for 8 weeks), conscious female Wistar (2 to 3 months) sedentary (S, N = 7) or trained rats (T, N = 7) were cannulated for direct arterial pressure (AP) recording in the non-ovulatory phases. Vagal (VT) and sympathetic tonus (ST) were evaluated by vagal (atropine) and sympathetic (propranolol) blockade. Baroreflex sensitivity was evaluated by the heart rate responses induced by AP changes. Cardiopulmonary reflex was measured by the bradycardic and hypotensive responses to serotonin. Resting bradycardia was observed in T (332 ± 7 bpm) compared with S animals (357 ± 10 bpm), whereas AP did not differ between groups. T animals exhibited depressed VT and ST (32 ± 7 and 15 ± 4 bpm) compared to S animals (55 ± 5 and 39 ± 10 bpm). The baroreflex and cardiopulmonary bradycardic responses were lower in T (-1.01 ± 0.27 bpm/mmHg and -17 ± 6 bpm) than in the S group (-1.47 ± 0.3 bpm/mmHg and -41 ± 9 bpm). Significant correlations were observed between VT and baroreflex (r = -0.72) and cardiopulmonary (r = -0.76) bradycardic responses. These data show that exercise training in healthy female rats induced resting bradycardia that was probably due to a reduced cardiac ST. Additionally, trained female rats presented attenuated bradycardic responses to baro- and cardiopulmonary receptor stimulation that were associated, at least in part, with exercise training-induced cardiac vagal reduction

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“…38 Although the concept of targeted therapy for both cardiovagal and sympathetic baroreflex sensitivity clearly requires further clinical validation, it is relevant to note that the enhancement of cardiovagal baroreflex function with regular exercise has been shown recently to occur through selective changes in the neural component. 39 Therefore, as an example, exercise prescription may be more effective in patients who experience morning orthostatic intolerance presenting with low neural sensitivity. Future work should be directed at understanding the changes in the mechanical and neural components of the baroreflex under different disease states and determining how baroreflex-enhancing effects of medications, such as angiotensin-converting enzyme inhibitors and ␤-blockers, 40 or lifestyle factors, such as a low-salt diet 41 and physical activity, 34 are ultimately achieved.…”

Section: Clinical Perspectivesmentioning

confidence: 99%

Diurnal Variation in the Mechanical and Neural Components of the Baroreflex

et al. 2011

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Abstract-Diminished baroreflex sensitivity in the morning negatively influences morning coronary blood flow and blood pressure control in hypertensive patients. Our aim was to determine the contribution of the mechanical and neural components of the cardiac baroreflex to diurnal variation in blood pressure control. In 12 healthy participants, we used the modified Oxford method to quantify baroreflex sensitivity for rising (G up ) and falling (G down ) pressures in the morning (7:00 AM) and afternoon (4:00 PM). Beat-to-beat blood pressure, R-R intervals, and carotid artery diameter measurements were recorded. Integrated sensitivity was determined by plotting R-R intervals against systolic blood pressure. The mechanical component was carotid artery diameter plotted against systolic blood pressure, and the neural component was R-R intervals plotted against carotid artery diameter. Linear mixed models were used to compare the integrated, mechanical, and neural sensitivities between morning and afternoon. We found significant diurnal variation in integrated sensitivity, with an attenuated response in the morning (G up ϭ13.0Ϯ0.6; G down ϭ6.3Ϯ0.4 ms/mm Hg) when compared with the afternoon (G up ϭ15.1Ϯ0.6; G down ϭ12.6Ϯ0.4 ms/mm Hg). For rising pressures, the diminished integrated sensitivity in the morning was caused by a reduction in mechanical sensitivity, whereas for falling pressures it was caused by a reduction in neural sensitivity. Our findings explicate the mechanisms underlying diurnal variation in baroreflex function. Pharmacological and lifestyle interventions targeted specifically at the diminished component of the cardiac baroreflex in the morning may lead to better management of hypertension. (Hypertension. 2011;58:51-56.)Key Words: circadian rhythms Ⅲ baroreflex Ⅲ blood pressure Ⅲ heart rate Ⅲ carotid artery B lood pressure (BP) exhibits a circadian rhythm, with the lowest pressures occurring during nocturnal sleep and a rapid "morning surge" after waking. 1 BP is most reactive to a given level of physical activity in the morning, 2 and risk of orthostatic intolerance is also greater at this time compared with the afternoon. 3 In a number of prospective studies (reviewed by Kario 4 ), the morning surge in BP has been found to be an independent risk factor for cardiovascular and cerebrovascular events, which also peak between 6:00 AM and 12:00 PM. 5,6 There is a wealth of evidence that BP control varies significantly over a 24-hour period, with studies in the frequency domain indicating the presence of a circadian rhythm in sympathovagal balance. 7,8 However, investigations directed at unraveling the autonomic mechanisms governing these time-of-day differences are lacking.The arterial baroreflex control of vagal neural outflow is quantified by the responses in R-R interval to changes in systolic BP. 9 Previous studies have identified diurnal variation in baroreflex sensitivity in both normotensive and hypertensive people, with reduced sensitivities after waking compared with during sleep. 10 -13 Moreover,...

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Arterial Baroreflex Control of Cardiac Vagal Outflow in Older Individuals Can Be Enhanced by Aerobic Exercise Training

Cited by 48 publications

References 61 publications

Intra-strain variations of baroreflex sensitivity in young Wistar-Kyoto rats

Intra-strain variations of baroreflex sensitivity in young Wistar-Kyoto rats

Tonic and reflex cardiovascular autonomic control in trained-female rats

Diurnal Variation in the Mechanical and Neural Components of the Baroreflex

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