Sympathetic Nerve Traffic Responses to Surgical Removal of Pheochromocytoma

Abstract

Abstract-Pheochromocytoma is usually characterized by a marked increase in peripheral catecholamine secretion.Whether this is accompanied by an alteration in central sympathetic drive has not been clarified. In 6 patients with adrenal pheochromocytoma (meanϮSEM age, 49.3Ϯ7.2 years), we measured systolic and diastolic blood pressure (photoplethysmographic device), heart rate (ECG), venous plasma catecholamines (high-performance liquid chromatography), and postganglionic muscle sympathetic nerve activity (microneurography) before and 78.3Ϯ13 days after surgical removal of the tumor. In each experimental session, measurements were performed during (1) a 60-minute resting period to compare several values of sympathetic nerve traffic at similar blood pressures before and after surgery and (2) voluntary end-expiratory apnea, ie, a maneuver inducing sympathetic activation. Tumor removal significantly (PϽ0.05 at least) reduced plasma catecholamines, blood pressure, and heart rate. In contrast, muscle sympathetic nerve activity was significantly (PϽ0.01) increased, both when quantified as bursts per minute (from 28.1Ϯ5.7 to 54.3Ϯ7.5) and as bursts per 100 heartbeats (from 33.4Ϯ5.6 to 65.1Ϯ6.5). This was also the case when data were evaluated in periods of 2 experimental sessions characterized by similar diastolic blood pressure values. The apnea maneuver induced sympathetic nerve traffic responses that were significantly (PϽ0.05) greater after surgery than before surgery. These data provide the first direct evidence that in pheochromocytoma central sympathetic outflow is markedly reduced and that this reduction cannot be ascribed to a reflex inhibitory response to elevated blood pressures. It is likely that this sympathoinhibition is rather due to a central depression of sympathetic outflow induced by high circulating catecholamines. (Hypertension. 1999;34:461-465.)Key Words: nervous system, sympathetic Ⅲ catecholamines Ⅲ nervous system, autonomic T he contribution of sympathetic nerve activity to blood pressure (BP) levels in pheochromocytoma is controversial. This is because it has been widely assumed that in this condition the BP elevation and the high level of circulating catecholamines should lead to a depression of sympathetic outflow by reflex mechanisms and direct stimulation of central adrenergic receptors, respectively. It has been reported, however, that in rats harboring a pheochromocytoma, pithing is accompanied by a clear-cut BP reduction, 1 pointing toward a sizable neural contribution to the BP elevation characterizing this condition. Furthermore, evidence has been produced that central sympathoinhibition by clonidine causes a similar BP reduction in patients with pheochromocytoma and with essential hypertension, 2 suggesting a similar degree of tonic sympathetic activity in both conditions.We have previously shown that muscle sympathetic nerve traffic as quantified by microneurography is much greater in patients with essential hypertension than in patients with a pheochromocytoma. 3 In the present study ...

Factors influencing arterial stiffness in pheochromocytoma and effect of adrenalectomy

“…This suggests that norepinephrine may be an important determinant contributing to increased arterial stiffness in patients with PHEO. Central sympathetic outflow probably does not contribute to the alteration of arterial stiffness in pheochromocytoma, since in previous study surgical removal of the tumor resulted in an increase of central sympathetic drive 30 .…”

Increased blood pressure variability in pheochromocytoma compared to essential hypertension patients

“…Two types of mechanisms leading to higher BP variability (especially during the daytime) in pheochromocytoma might be taken into consideration: first, the ability of circulating catecholamines to cause rapid BP elevations, and second, a high incidence of orthostatic hypotension with normally functioning baroreflex [19][20][21] probably related to the tendency to hypovolemia [22,23] or because of the suppressed central sympathetic outflow [24] as a consequence of the hyperactivation of adrenergic receptors, especially in patients with pheochromocytoma secreting norepinephrine [25].…”

Modafinil Elicits Sympathomedullary Activation

“…30 Such a constellation of tachycardia, hypertension, and decreased MSNA occurs also in the fight or flight response, 31,32 after tyramine infusion, 33 and in pheochromocytoma patients. 34 It has been observed that in sleep apnea, which is associated with higher sympathetic tone; modafinil did not elevate the resting sympathetic tone further, although sympathetic effect on mental and physical load could be shown. 10 Unlike modafinil, other psychostimulants such as amphetamine elevated plasma NE, systolic and diastolic BP, but not HR or plasma Epi.…”