The short term secretion pattern of human serum melatonin indicates apulsatile hormone release

Area of Science:

• Endocrinology
• Chronobiology
• Neuroscience

Background:

• Hormone secretion is often pulsatile, with frequency and amplitude changes impacting physiology.
• Previous studies on short-term melatonin (MLT) secretion patterns yielded inconsistent results.
• Advancements in MLT assays and pulse detection software necessitate re-evaluation of MLT secretion.

Purpose of the Study:

• To re-examine the short-term secretion pattern of the pineal hormone melatonin (MLT).
• To determine if MLT is secreted in a pulsatile or apulsatile manner in healthy volunteers.

Main Methods:

• Collected blood samples at 3- and 10-minute intervals from 16 healthy volunteers over extended periods.
• Measured serum MLT concentrations using a sensitive radioimmunoassay (RIA).
• Analyzed MLT level sequences for pulses using visual inspection and computer programs (Pulsar, Cluster).

Main Results:

• Analysis revealed continuous release of MLT throughout the day and night, without clear pulsatile patterns.
• Statistical and computer-based pulse detection methods did not identify significant MLT pulses beyond the circadian rhythm.
• The study demonstrated apulsatile secretion of MLT, contrasting with many other endocrine hormones.

Conclusions:

• Melatonin (MLT) is secreted in an apulsatile manner, differing from the typical pulsatile release of many hormones.
• Frequent blood sampling may be redundant for fully characterizing MLT secretion patterns.
• The pineal gland's MLT secretion does not appear to be controlled by a hypothalamic or intrinsic pulse generator, beyond the circadian pacemaker.