Baroreflex Control of Sympathetic Nerve Activity in Essential and Secondary Hypertension

Abstract

Abstract-Studies performed in experimental animals and in humans have documented that high blood pressure markedly impairs baroreceptor control of heart rate. Whether a similar impairment also characterizes baroreceptor control of sympathetic activity modulating peripheral vasomotor tone is still unknown. In 28 untreated essential hypertensive subjects [14 of moderate and 14 of more severe degree, age 51.6Ϯ2.4 and 52.6Ϯ2.1 years (meanϮSEM)] and in 13 untreated secondary hypertensives (renovascular or pheochromocytoma, age 50.1Ϯ4.6 years), we measured beat-to-beat arterial blood pressure (finger photoplethysmographic device), heart rate (electrocardiogram), and efferent postganglionic muscle sympathetic nerve activity (microneurography) at rest and during baroreceptor stimulation and deactivation induced by stepwise intravenous infusions of phenylephrine and nitroprusside, respectively. Data were compared with those obtained in 15 age-matched normotensive control subjects. Muscle sympathetic nerve activity (bursts per 100 heart beats) showed a progressive and significant (PϽ.01) increase from normotension (40.3Ϯ3.3) to moderate (55.6Ϯ4.1) and more severe essential hypertension (68.2Ϯ4.1), paralleling the progressive increase in blood pressure values. In contrast, muscle sympathetic nerve activity was not increased in secondary hypertensives (40.5Ϯ6.7) despite blood pressure values similar to or even greater than those of severe essential hypertensives. In both essential and secondary hypertensives, baroreceptor-heart rate control was displaced toward elevated blood pressure values and markedly impaired compared with normotensive subjects (average reduction, 38.5%). In contrast, the sympathoinhibitory and sympathoexcitatory responses to baroreceptor stimulation and deactivation were displaced toward elevated blood pressure values but similar in all groups. Thus, sympathetic activation characterizes essential but not secondary hypertension. Regardless of its nature, however, hypertension is not accompanied by an impairment of baroreceptor modulation of sympathetic activity. Key Words: sympathetic nervous system Ⅲ autonomic nervous system Ⅲ baroreceptors Ⅲ hypertension, essential C onclusive evidence shows that baroreceptor modulation of heart rate is impaired in animals and patients with high blood pressure.1-3 Whether baroreceptor modulation of vasomotor tone is similarly affected is controversial, however. This is because although some studies have reported vascular, blood pressure, and sympathetic responses to baroreceptor manipulation to be reduced in hypertensive animals and humans, [4][5][6] other studies have found vascular, blood pressure, and sympathetic effects of alterations in baroreceptor activity to be unmodified or enhanced in experimental or human hypertension as compared with the normotensive condition. [7][8][9][10][11] This has led to the hypothesis that baroreceptor control of the cardiovascular functions is desmogenously affected by high blood pressure, ie, that this condition impairs barorecep...

Endogenous leptin contributes to baroreflex suppression within the solitary tract nucleus of aged rats

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Sympathetic Overdrive and Cardiovascular Risk in the Metabolic Syndrome

“…This is shown in Fig. 2, which refers to the results of a microneurographic study performed by our group in mild and more severe essential hypertensive patients (10). Indeed, when the nerve firing rate, i.e., the number of sympathetic bursts over time or corrected for heart rate, was assessed in normotensive middle-age subjects and in untreated age-matched patients displaying blood pressure elevations of increasing severity, the results showed that not only mild but also more severe essential hypertension was characterized by sympathetic overactivity.…”

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Simvastatin reduces sympathetic activity in men with hypertension and hypercholesterolemia

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