¹Division of Hypertension University of Michigan, Ann Arbor, MI, USA

Abstract

Increased sympathetic (SYMP) tone and higher blood pressure (BP) levels are often associated.

We tested the hypothesis that: a) increased SYMP tone relates to overweight, b) it elicits beta adrenoreceptor (BAR) down-regulation which, c) decreases BAR mediated energy expenditure (EE) and causes overweight (OW).

We recruited subjects with a wide spread of BPs (systolic 95-180, 123 20, diastolic 43-106, 78 16 mmHg) and weights (47-150, 84 23 Kg). 18 were normotensives (11 men) and 20 (11 men) untreated hypertensives.

Measurements included, on Day 1, heart rate (HR) changes to isoproterenol (ISO) boluses (highest 2g/m²); on Day 2, metabolic and hemodynamic changes to ISO infusions (highest 40 ng/Kg/min).

Resting HR correlated with skinfold thickness (SKIN) (r= 0.53, p< 0.0006. Plasma and urinary norepinephrine (NE) correlated but not significantly to SKIN (r= 0.3, p< 0.07; r= 0.26, p< 0.16) respectively). Baseline HR correlated negatively with HR change to ISO bolus (r= -0.60, p< 0.0009) and infusion (r= -0.55, p< 0.01) and with glucose changes to ISO infusion (r= -0.50, p< 0.03). Urinary NE correlated negatively with EE (r= -0.51, p< 0.04). HR response to ISO bolus correlated negatively with SKIN (r= -0.56, p< 0.003). Systolic and diastolic (not shown) BP correlated with SKIN (p= 0.45, p< 0.005) and baseline HR (r= 0.37, p< 0.03). SBP correlated negatively with HR change to ISO bolus (r= -0.39, p< 0.05) and with glucose response to ISO infusion (r= -0.51, p< 0.04).

In conclusion, resting SYMP tone is associated with OW, higher BP, and decreased beta-1 (HR) and beta-2 (glucose) responsiveness. Decreased beta-1 responsiveness is associated with overweight. The EE response was not related to weight or to BAR responsiveness. SYMP was associated with higher BP, OW and decreased BAR responsiveness. Decreased BAR responsiveness related to OW and higher BP, but we failed to prove a link between decreased EE and decreased BAR responsiveness.