Experimental hyperleptinemia acutely increases vasoconstrictory sympathetic nerve activity in healthy humans

Background: Obesity and arterial hypertension are tightly connected. Obese individuals show significant elevation of vasoconstrictory muscle sympathetic nerve activity (MSNA). Obesity-related hyperleptinemia might play a key role in mediating these effects. Leptin is synthesized in proportion to body fat mass and activates SNA in animal models. In humans, however, direct evidence linking hyperleptinemia to sympathetic activation has not yet been established. In the present study, we characterize the effects of acute hyperleptinemia on microneurographically recorded SNA in humans. Methods: In a balanced, double-blind crossover design, 12 healthy normal-weight males received an iv bolus of leptin or placebo. MSNA (bursts per minute) was continuously recorded using a microneurographic technique. Ten-minute periods were analyzed at resting periods before (t_-100) and at 20 (t₂₀), 60 (t ₆₀), and 140 (t₁₄₀) minutes after substance administration. Blood pressure and heart rate (HR) were recorded simultaneously. Results: Baseline values of MSNA, blood pressure, and HR were comparable in both conditions (MSNA: t_-100, 24.3 ± 1.6 vs 22.7 ± 1.7, not significant). After application of leptin, MSNA showed a significant increase (t₂₀, 31.0 ± 1.9 vs. 24.9 ± 1.8, P = .05) that persisted until the end of the experiment (t₆₀, P = .008; t ₁₄₀, P = .004). There were no significant changes in blood pressure and HR. Conclusions: Acute experimental hyperleptinemia has significant central nervous excitatory effects on vasoconstrictory sympathetic outflow as measured by MSNA in healthy men. These results suggest that leptin acts as an important mediator linking obesity to elevated MSNA and potentially to the development of hypertension.