Fasting alters pulsatile and rhythmic cortisol release in normal man.

Area of Science:

• Endocrinology
• Human Physiology
• Metabolic Research

Background:

• Cortisol, a key stress hormone, exhibits complex pulsatile and periodic release patterns.
• Fasting is a significant physiological stressor known to influence hormonal regulation.
• Understanding cortisol dynamics during fasting is crucial for metabolic and endocrine research.

Purpose of the Study:

• To investigate the effects of a 5-day fast on integrated, pulsatile, and periodic cortisol release in healthy men.
• To quantify changes in serum cortisol concentrations and urinary cortisol excretion during fasting.
• To analyze alterations in circadian and ultradian cortisol rhythms.

Main Methods:

• Serum cortisol concentrations were measured every 20 minutes for 24 hours before and on the fifth day of fasting in 10 men.
• Cortisol profiles were analyzed for integrated release (AUC), pulsatile release (cluster analysis), and periodic release (Fourier analysis).
• 24-hour urinary cortisol excretion was measured in 5 men.

Main Results:

• Mean 24-hour integrated serum cortisol increased 1.7-fold during fasting, driven by higher inter-pulse levels and pulse amplitude.
• No significant changes were observed in the number, interval, width, or area of cortisol pulses.
• 24-hour urinary cortisol excretion increased, and the circadian rhythm amplitude decreased, while 12-h and shorter ultradian rhythm amplitudes increased.

Conclusions:

• A 5-day fast induces significant alterations in the amount and pattern of cortisol release, affecting pulsatile, circadian, and ultradian dynamics.
• Fasting leads to increased overall cortisol exposure and shifts in rhythmic patterns, highlighting its impact on the hypothalamic-pituitary-adrenal axis.
• These findings provide insights into the endocrine adaptations to prolonged fasting.