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Related Experiment Videos

Effects of clonidine on sympathetic function.

E L Bravo

    Chest
    |February 1, 1983
    PubMed
    Summary
    This summary is machine-generated.

    Clonidine effectively lowers blood pressure in essential hypertension by reducing sympathetic activity. However, in pheochromocytoma, it lowers blood pressure without affecting norepinephrine levels, suggesting different mechanisms.

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    Area of Science:

    • Pharmacology
    • Cardiovascular Medicine
    • Endocrinology

    Background:

    • Essential hypertension and pheochromocytoma involve dysregulated sympathetic nervous system activity.
    • Clonidine is a centrally acting antihypertensive agent.
    • Understanding clonidine's effects on sympathetic indices is crucial for its clinical application.

    Purpose of the Study:

    • To investigate the impact of clonidine on sympathetic function markers in patients with essential hypertension and pheochromocytoma.
    • To compare the biochemical and functional responses to clonidine in these two distinct hypertensive conditions.

    Main Methods:

    • A study involving 15 patients with essential hypertension and 10 with pheochromocytoma.
    • Administration of a single oral dose of clonidine (0.3 mg).

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  • Measurement of supine plasma norepinephrine, plasma renin activity, blood pressure, and heart rate, including responses to head-up tilt.

    • Main Results:

    • Clonidine significantly decreased supine plasma norepinephrine in essential hypertension but not in pheochromocytoma.
    • Blood pressure and heart rate reductions were observed in both groups.
    • Head-up tilt after clonidine administration in essential hypertension showed reduced blood pressure but increased heart rate and plasma norepinephrine.
    • Plasma renin activity remained unchanged in both groups.

    Conclusions:

    • Clonidine may lower blood pressure by inhibiting sympathetic outflow, with plasma renin activity playing a minor role.
    • In pheochromocytoma, clonidine's antihypertensive effect occurs independently of changes in plasma norepinephrine, highlighting the significance of neuronally released norepinephrine over circulating catecholamines.