Suppression of sympathetic nervous system during fasting

Area of Science:

• Cardiovascular Physiology
• Neuroendocrinology
• Metabolic Research

Background:

• Norepinephrine (NE) is a key neurotransmitter in sympathetic nervous system (SNS) regulation of cardiovascular function.
• Fasting is known to induce significant metabolic and physiological adaptations.
• The impact of fasting on central sympathetic outflow and cardiac NE turnover requires further elucidation.

Purpose of the Study:

• To investigate the effect of short-term fasting on cardiac norepinephrine turnover in rats.
• To determine the role of central sympathetic activity in mediating fasting-induced changes in cardiac NE.
• To assess the reversibility of these changes upon refeeding.

Main Methods:

• Rats were subjected to a two-day fasting protocol.
• Ganglionic blockade was administered to both fasted and fed control rats.
• Cardiac norepinephrine turnover was assessed using [3H]-norepinephrine retention and endogenous norepinephrine levels.

Main Results:

• Two days of fasting significantly reduced cardiac norepinephrine turnover.
• Ganglionic blockade had no significant effect on [3H]-norepinephrine retention or endogenous norepinephrine in fasted rats, unlike in fed controls.
• One day of refeeding completely reversed the decrease in norepinephrine turnover.

Conclusions:

• Fasting suppresses centrally mediated sympathetic activity to the heart.
• Cardiac norepinephrine turnover is sensitive to nutritional status and central sympathetic drive.
• Refeeding rapidly restores sympathetic activity and norepinephrine turnover, highlighting the dynamic interplay between metabolism and the nervous system.