Increased sympathetic activity in rat white adipose tissue during prolonged fasting

Area of Science:

• Physiology
• Metabolism
• Adipose Tissue Biology

Background:

• Sympathetic nervous system plays a crucial role in regulating energy balance and adipose tissue metabolism.
• White adipose tissue (WAT) and brown adipose tissue (BAT) exhibit distinct roles and responses to metabolic challenges.
• Understanding the impact of fasting on sympathetic activity in different adipose depots is vital for metabolic research.

Purpose of the Study:

• To investigate the differential effects of prolonged fasting on sympathetic activity in rat white adipose tissue (WAT) and interscapular brown adipose tissue (IBAT).
• To elucidate the role of norepinephrine (NE) turnover and uptake in WAT and IBAT during fasting.
• To determine if fasting-induced changes in sympathetic activity contribute to lipolysis in WAT.

Main Methods:

• Rats were subjected to 48-hour fasting or maintained on a fed diet.
• Norepinephrine (NE) content and [3H]NE uptake were measured in WAT and IBAT.
• NE fractional rates and calculated turnover rates were determined using DL-alpha-methyl-p-tyrosine and [3H]NE.

Main Results:

• Fasting significantly increased [3H]NE uptake and NE turnover in WAT (retroperitoneal and epididymal depots).
• In contrast, fasting led to a 50% reduction in [3H]NE uptake and decreased NE turnover in IBAT.
• Tissue NE content was not significantly affected by 48-hour fasting in either WAT or IBAT.

Conclusions:

• Prolonged fasting selectively activates sympathetic nervous system fibers innervating white adipose tissue (WAT).
• This selective activation in WAT promotes lipolysis, contributing to energy mobilization during fasting.
• The sympathetic response in brown adipose tissue (BAT) is suppressed during fasting, suggesting depot-specific adaptations.