Nervous activity varies with hypertension type

2 October 2007

MedWire News: Obese and non-obese patients with hypertension have different patterns of sympathetic nervous activity, results from the journal Hypertension indicate.

"A neural basis for hypertension exists both in the setting of obesity and also for hypertension in the non-obese," explain Elisabeth Lambert and team from the Baker Heart Research Institute in Melbourne, Australia.

Noting that the effects of hypertension on health vary greatly in obese and non-obese individuals, Lambert and colleagues speculated that activation of the sympathetic nervous system may differ in obese and lean individuals with the condition.

To test this hypothesis, the researchers analyzed nerve firing, as a characteristic of sympathetic activation in 10 lean individuals with hypertension and 14 obese individuals with hypertension.

Lambert and co-workers found that single vasoconstrictor fibers were significantly more active in lean than in obese hypertensives (70 vs 28 spikes per 100 heartbeats). Firing probability per heartbeat was also significantly higher in lean compared with obese individuals (39% vs 20%), as was the incidence of multiple spikes per heartbeat (30% vs 17%).

In contrast, sympathetic activity in the obese participants was characterized by the recruitment of previously silent fibers, which fired at a normal rate.

Discussing the implications of these differences, Lambert et al suggest that the high cardiac sympathetic activity seen in the lean patients probably promotes left ventricular hypertrophy and accounts for the poorer cardiovascular prognosis seen in lean compared with obese hypertensives.

Although they found clear differences in nervous system activation in their study, the authors admit that the ways in which these variations might be exploited pharmacologically remain to be elucidated.

Hypertension 2007; 50: Advance online publication