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(Circulation. 2003;108:3097-3101.)
© 2003 American Heart Association, Inc.

Clinical Investigation and Reports

Impact of Type 2 Diabetes Mellitus on Sympathetic Neural Mechanisms in Hypertension

Robert J. Huggett, MB, BS; Eleanor M. Scott, BM, BS, MD; Stephen G. Gilbey, BA, MD; John B. Stoker, BSc, MB, ChB; Alan F. Mackintosh, MA, MD; David A.S.G. Mary, MB, ChB, PhD

From the Department of Cardiology (R.J.H., J.B.S., A.F.M., D.A.S.G.M.) and Diabetes & Endocrinology (E.M.S., S.G.G.), St James’s University Hospital, Leeds, United Kingdom.

Correspondence to Dr R.J. Huggett, Department of Cardiology, St James’s University Hospital, Beckett St, Leeds LS9 7TF, United Kingdom. E-mail roberthuggett{at}hotmail.com

Received April 3, 2003; de novo received July 18, 2003; revision received September 19, 2003; accepted September 22, 2003.

Background— Essential hypertension (EHT) is a major cardiovascular risk factor, and the additional presence of type 2 diabetes mellitus (DM2) increases this risk. However, although the sympathetic nerve hyperactivity of EHT is known to play a role in cardiovascular risk, the level of sympathetic nerve activity is known neither in DM2 nor in hypertensive type 2 diabetic patients (EHT+DM2). Therefore, we planned to quantify the vasoconstrictor sympathetic nerve activity in patients with EHT+DM2 and with DM2 relative to that in matched groups with EHT and normal blood pressure (NT).

Methods and Results— In 68 closely matched subjects with EHT+DM2 (n=17), DM2 (n=17), EHT (n=17), and NT (n=17), we measured resting muscle sympathetic nerve activity as the mean frequency of multiunit bursts (MSNA) and of single units (s-MSNA) with defined vasoconstrictor properties. The s-MSNA in EHT+DM2 (97±3.8 impulses/100 beats) was greater (at least P<0.001) than in EHT (69±3.4 impulses/100 beats) and DM2 (78±4.1 impulses/100 beats), and all these were significantly greater (at least P<0.01) than in NT (53±3.3 impulses/100 beats) despite similar age and body mass index. The MSNA followed a similar trend. In addition, the level of insulin was also raised in EHT+DM2 (20.4±3.6 µU/mL) and DM2 (18.1±3.1 µU/mL; at least P<0.05) compared with HT or NT.

Conclusions— Patients with EHT+DM2, EHT, or DM2 had central sympathetic hyperactivity, although plasma insulin levels were raised only in EHT+DM2 and DM2. The combination of EHT and DM2 resulted in the greatest sympathetic hyperactivity and level of plasma insulin, and this hyperactivity could constitute a mechanism for the increased risks of this condition.

Key Words: nervous system, sympathetic • hypertension • diabetes mellitus

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