Impact of type 2 diabetes mellitus on sympathetic neural mechanisms in hypertension

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 muU/mL) and DM2 (18.1 +/- 3.1 muU/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.