Suppression of sympathetic nervous system during fasting

Area of Science:

• Cardiovascular Physiology
• Neuroendocrinology
• Metabolic Regulation

Background:

• Norepinephrine (NE) is a key neurotransmitter in sympathetic nervous system (SNS) regulation of cardiovascular function.
• Nutritional status, such as fasting and refeeding, is known to influence autonomic nervous system activity.
• The specific impact of short-term fasting on cardiac norepinephrine turnover and central sympathetic outflow requires further elucidation.

Purpose of the Study:

• To investigate the effect of a two-day fasting period on cardiac norepinephrine turnover in rats.
• To examine the role of central sympathetic activity in mediating changes in cardiac norepinephrine during fasting.
• To determine if refeeding can reverse the observed effects of fasting on cardiac norepinephrine metabolism.

Main Methods:

• Assessment of norepinephrine turnover in rat hearts following a two-day fasting period.
• Pharmacological blockade of ganglionic transmission in both fasted and fed rats.
• Measurement of [3H]-norepinephrine retention and endogenous norepinephrine levels in cardiac tissue.

Main Results:

• Two days of fasting significantly reduced norepinephrine turnover in the heart.
• Ganglionic blockade did not significantly affect norepinephrine retention or levels in fasted rats, unlike in fed controls.
• The observed decrease in cardiac norepinephrine turnover during fasting was fully reversed after one day of refeeding.

Conclusions:

• Fasting suppresses centrally mediated sympathetic activity directed to the heart.
• Cardiac norepinephrine metabolism is sensitive to nutritional state, with fasting decreasing turnover and refeeding restoring it.
• These findings underscore the intricate link between metabolic status and autonomic nervous system regulation of the cardiovascular system.