Attenuated baroreflex control of sympathetic nerve  activity after cardiovascular deconditioning in rats

Moffitt, Julia A.; Foley, C. Michael; Schadt, James C.; Laughlin, M. Harold; Hasser, Eileen M.

doi:10.1152/ajpregu.1998.274.5.r1397

Cited by 55 publications

(120 citation statements)

References 36 publications

(92 reference statements)

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“…In addition, hindlimb unloading in rats, which simulates the effect of spaceflight or bed rest (21, 36), also produces blunted baroreflex activation of the sympathetic nervous system (14,34). These data are consistent with findings that deficits in peripheral vasoconstriction contribute importantly to orthostatic intolerance observed in susceptible individuals after spaceflight or bed rest (5,31,66).…”

supporting

confidence: 66%

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Regulation of plasma vasopressin and renin activity in conscious hindlimb-unloaded rats

Mueller¹,

Sullivan²,

Grindstaff³

et al. 2006

American Journal of Physiology-Regulatory, Integrative and Comp

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. Regulation of plasma vasopressin and renin activity in conscious hindlimb-unloaded rats. Am J Physiol Regul Integr Comp Physiol 291: R46 -R52, 2006. First published February 9, 2006 doi:10.1152/ajpregu.00622.2005.-Cardiovascular deconditioning occurs in astronauts after spaceflight or in individuals subjected to bed rest. It is characterized by an increased incidence of orthostatic intolerance. The mechanisms responsible for orthostatic intolerance are likely multifactorial and may include hypovolemia, autonomic dysfunction, and vascular and cardiac alterations. The arterial baroreflex is an important compensatory mechanism in the response to an orthostatic stress. In a previous study, we demonstrated that arterial baroreflex mediated sympathoexcitation was blunted in hindlimb-unloaded (HU) rats, a model of cardiovascular deconditioning. The arterial baroreflex also contributes to the regulation of vasoactive hormones including vasopressin and angiotensin II. In the present study, we tested the hypothesis that the neurohumoral response to hypotension is also attenuated in rats after 14 days of hindlimb unloading. To test this hypothesis, the vasodilator diazoxide (15 or 25 mg/kg) or saline (0.9%) was administered to produce hypotension or control conditions, respectively, in conscious HU and control rats. Plasma samples were collected and assayed for vasopressin and plasma renin activity (PRA). Diazoxide (25 mg/kg) produced significant increases in vasopressin and PRA compared with saline controls. HU rats exhibited significantly higher levels of vasopressin at rest and the increase in vasopressin levels during hypotension was enhanced by hindlimb unloading. Neither resting nor hypotension-induced PRA was altered by hindlimb unloading. These data suggest that although baroreflex-mediated sympathoexcitation is blunted by hindlimb unloading, hypotension-induced vasopressin release is enhanced and hypotension-induced PRA is unaffected. Increased circulating vasopressin may serve to compensate for blunted baroreflex regulation of sympathetic nervous activity produced by hindlimb unloading or may actually contribute to it. neurohumoral control; antidiuretic hormone; renin-angiotensin system ASTRONAUTS RETURNING FROM space, or individuals recovering from prolonged bed rest often experience symptoms of orthostatic intolerance (5,8,16,31,54,65). To delineate the possible mechanisms mediating orthostatic intolerance, individuals have been categorized as presyncopal or nonpresyncopal (17, 31, 66), finishers and nonfinishers (5), or simply, orthostatic tolerant and intolerant (54). No matter what nomenclature is used, the common characteristic among these individuals is an inability to maintain arterial pressure during an orthostatic challenge.Compensations for orthostatic stress include baroreflexmediated increases in heart rate in an attempt to maintain cardiac output, as well as increases in total peripheral resistance to maintain adequate arterial pressure (47). Initially, vasoconstriction is accomplished through a...

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confidence: 66%

“…Male Sprague-Dawley rats (260 -350 g, Harlan, Indianapolis, IN) were HU or maintained under control conditions for 14 days, according to methods described previously (34,36,38). Briefly, rats were initially tail suspended for short periods (1-3 h/day) over 3 days to acclimate them to hindlimb unloading conditions.…”

Section: Methodsmentioning

confidence: 99%

Regulation of plasma vasopressin and renin activity in conscious hindlimb-unloaded rats

Mueller¹,

Sullivan²,

Grindstaff³

et al. 2006

American Journal of Physiology-Regulatory, Integrative and Comp

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“…After bed rest or spaceflight, baseline arterial baroreflex regulation of HR is reduced (46). In rats, after 14 days of hindlimb unloading, sympathetic activation to muscle, renal, and lumbar vascular beds during a hypotensive stimulus appears to be blunted (68). In humans, after 14 days prolonged bed rest, postural hypotension in orthostatic intolerant subjects is associated with blunted responses of MSNA (Fig.…”

Section: Physiological Changes In Baroreflex Functionmentioning

confidence: 99%

“…37). Among the potential mechanisms contributing to orthostatic intolerance associated with deconditioning (including hypovolemia, inadequate maintenance of stroke volume, and vascular dysfunction) is altered autonomic function (46,68,105). After bed rest or spaceflight, baseline arterial baroreflex regulation of HR is reduced (46).…”

Section: Physiological Changes In Baroreflex Functionmentioning

confidence: 99%

Arterial baroreflex function and cardiovascular variability: interactions and implications

Lanfranchi

Somers

2002

American Journal of Physiology-Regulatory, Integrative and Comp

251

183

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The arterial baroreflex contributes importantly to the short-term regulation of blood pressure and cardiovascular variability. A number of factors (including reflex, humoral, behavioral, and environmental) may influence gain and effectiveness of the baroreflex, as well as cardiovascular variability. Many central neural structures are also involved in the regulation of the cardiovascular system and contribute to the integrity of the baroreflex. Consequently, brain injuries or ischemia may induce baroreflex impairment and deranged cardiovascular variability. Baroreflex dysfunction and deranged cardiovascular variability are also common findings in cardiovascular disease. A blunted baroreflex gain and impaired heart rate variability are predictive of poor outcome in patients with heart failure and myocardial infarction and may represent an early index of autonomic activation in left ventricular dysfunction. The mechanisms mediating these relationships are not well understood and may in part be the result of cardiac structural changes and/or altered central neural processing of baroreflex signals.

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“…Electrode Surgical Implantation-Surgical procedures for the placement of femoral catheters and lumbar sympathetic recording electrodes were conducted under halothane anesthesia, using aseptic surgical techniques, similar to procedures described previously (28). Polyethylene (PE 10 fused to PE 50) catheters were inserted into the aorta and abdominal vena cava via the left femoral artery and vein for measurement of arterial pressure and administration of vasoactive drugs, respectively.…”

Section: Catheter and Lumbar Sympathetic Nerve Recordingmentioning

confidence: 99%

Evaluation of Baroreceptor Reflex Function in the Chronic Mild Stress Rodent Model of Depression

Grippo

Moffitt²,

Johnson³

2008

Psychosomatic Medicine

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Objective-There is a bidirectional relationship between mood disorders (e.g., depression) and altered cardiovascular regulation (e.g., heart disease), however the precise causal and/or common mechanisms underlying this association are unclear. In previous studies we have noted indications of altered sympathetic drive to the heart in rats that exhibit anhedonia, an operational sign of depression induced by subjecting the animals to a series of mild and unpredictable stressors [chronic mild stress (CMS) rodent model of depression]. The purpose of the present study was to more fully characterize baroreceptor reflex function in rats with experimentally-induced depression.Methods-Male, Sprague-Dawley rats were exposed to either 4 weeks of mild, unpredictable stressors (CMS group) or standard housing conditions (control group). Depression-like behavior, resting hemodynamic and cardiac parameters, and baroreceptor reflex function were investigated in all animals following the CMS period.Results-CMS produced anhedonia, evidenced by reduced sucrose intake and sucrose preference, as well as elevated resting heart rate (HR), slightly elevated blood pressure, and reduced HR variability. These animals also exhibited significantly attenuated sympathoexcitatory responses to hypotension, and an elevation of basal sympathetic nerve activity.Conclusions-These findings suggest that CMS is associated with altered sympathoexcitatory responses following baroreceptor unloading and provide further insights into potential common mechanisms underlying the association of depression and altered cardiovascular control.

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Attenuated baroreflex control of sympathetic nerve activity after cardiovascular deconditioning in rats

Cited by 55 publications

References 36 publications

Regulation of plasma vasopressin and renin activity in conscious hindlimb-unloaded rats

Regulation of plasma vasopressin and renin activity in conscious hindlimb-unloaded rats

Arterial baroreflex function and cardiovascular variability: interactions and implications

Evaluation of Baroreceptor Reflex Function in the Chronic Mild Stress Rodent Model of Depression

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