Receptor-mediated regional sympathetic nerve activation by leptin

Area of Science:

• Neuroendocrinology
• Physiology
• Metabolism

Background:

• Leptin is a key hormone regulating energy balance, produced by adipose tissue.
• While leptin influences appetite and energy expenditure centrally, its direct impact on sympathetic nerve activity is not fully understood.
• Previous studies suggest leptin affects norepinephrine turnover, hinting at sympathetic nervous system involvement.

Purpose of the Study:

• To investigate the direct effects of leptin on sympathetic nerve activity in various tissues.
• To determine if leptin influences sympathetic outflow to thermogenic and non-thermogenic organs.
• To assess the dose-dependency and physiological consequences of leptin-induced sympathetic activation.

Main Methods:

• Intravenous administration of leptin or vehicle to anesthetized Sprague-Dawley rats.
• Direct measurement of sympathetic nerve activity in brown adipose tissue, kidney, hindlimb, and adrenal gland.
• Analysis of dose-response relationships and effects in obese Zucker rats with leptin receptor mutations.

Main Results:

• Leptin significantly increased sympathetic nerve activity to brown adipose tissue, kidney, hindlimb, and adrenal gland in a dose-dependent manner.
• A threshold dose of 100 microg/kg was identified for leptin's sympathoexcitatory effects.
• Despite increased sympathetic activity, leptin did not alter arterial pressure, heart rate, plasma glucose, or insulin levels.
• Obese Zucker rats exhibited resistance to leptin's sympathoexcitatory effects, indicating the role of the leptin receptor.

Conclusions:

• Leptin administration directly stimulates sympathetic nerve activity to multiple tissues, including thermogenic brown adipose tissue.
• The findings reveal an unexpected stimulatory role of leptin on overall sympathetic nerve traffic.
• Leptin receptor integrity is crucial for mediating leptin's sympathoexcitatory effects, as demonstrated by the resistance in obese Zucker rats.