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Plasma free cortisol during secretory episodes.

M Follenius, G Brandenberger

    The Journal of Clinical Endocrinology and Metabolism
    |March 1, 1986
    PubMed
    Summary
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    Free cortisol levels in men fluctuate with total cortisol, rising during natural or stimulated peaks. These variations in free cortisol do not explain differing cortisol responses to stimuli.

    Area of Science:

    • Endocrinology
    • Human Physiology

    Background:

    • Cortisol, a key stress hormone, circulates in plasma bound to proteins and as a free, biologically active fraction.
    • Understanding the dynamics of free cortisol is crucial for interpreting hormonal responses to various stimuli.

    Purpose of the Study:

    • To investigate the relationship between plasma free cortisol fractions and total cortisol during physiological secretory episodes and stimulated peaks in healthy men.
    • To determine if variations in free cortisol percentage influence the body's response to subsequent stimuli.

    Main Methods:

    • Plasma samples were collected from normal men during spontaneous and ACTH- or exercise-induced cortisol secretory episodes.
    • Free cortisol percentage was quantified using ultrafiltration at 37°C.
    • Total cortisol concentrations were measured via radioimmunoassay (RIA).

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    Main Results:

    • Plasma free cortisol percentage exhibited diurnal variations, mirroring total cortisol levels.
    • Free cortisol increased in parallel with total cortisol during spontaneous (e.g., morning, postprandial) and stimulated (ACTH, exercise) events.
    • A strong positive correlation was observed between relative increases in free and total cortisol.
    • The study found no evidence that variations in free cortisol percentage account for differences in cortisol responses to subsequent stimuli.

    Conclusions:

    • Plasma free cortisol levels dynamically follow total cortisol concentrations throughout the day and in response to stimuli.
    • The percentage of free cortisol does not appear to be the primary factor modulating the differential responses to subsequent cortisol-stimulating events.