Decreased adrenergic tone in acromegaly: evidence from direct recording of muscle sympathetic nerve activity

Objective:  Sympathovagal imbalance has been shown in acromegaly by indirect measurements of adrenergic tone. Data regarding direct measurement of sympathetic activity are lacking as yet. Aim of this study was to assess the adrenergic tone through direct recording of muscle sympathetic nerve activity (MSNA) in acromegalic patients Design:  Fifteen patients (age 26-66 years, 8 females) with newly diagnosed active acromegaly without hyperprolactinemia, pituitary hormone deficiencies, obstructive sleep apnoea and cardiac hypertrophy, and 15 healthy subjects matched for age, sex and body mass index were recruited. After evaluating anthropometric and echocardiographic parameters, anterior pituitary function, glucose and lipid metabolism, and measuring plasma leptin, direct recording of sympathetic outflow via the microneurographic technique was performed. Results:  For similar anthropometric and metabolic parameters in patients and controls, HOMA index was significantly increased in the former (4.2 ± 2.39 vs 1.6 ± 0.19, P < 0.001). Surprisingly, this finding of insulin resistance was accompanied by a marked sympathetic inhibition (MSNA 18.3 ± 8.10 vs 37.3 ± 6.48 bursts/min, P < 0.0001, respectively in patients and controls). A reduction of plasma leptin (1.6 ± 1.04 vs 6.5 ± 2.01 μg/l, P < 0.0001) was also recorded in the patients. MSNA was positively correlated with leptin (P < 0.0001). Conclusions:  Newly diagnosed acromegalic patients without cardiac hypertrophy display a decreased sympathetic outflow in spite of insulin resistance. This finding might be related to hypoleptinemia.