Effects of bromocriptine on plasma catecholamines in normal men

Area of Science:

• Pharmacology
• Neuroendocrinology
• Cardiovascular Physiology

Background:

• Dopamine (DA) receptor agonists influence neuroendocrine and cardiovascular functions.
• Bromocriptine (Brc) is a DA agonist with known effects on prolactin secretion.
• The impact of Brc on peripheral catecholamine (CA) levels requires further elucidation.

Purpose of the Study:

• To investigate the acute and short-term effects of bromocriptine on plasma catecholamine concentrations in healthy male volunteers.
• To compare the time course of Brc's effects on catecholamines versus prolactin.
• To assess Brc's influence on catecholamine responses to postural change and its potential clinical utility.

Main Methods:

• Administration of a single oral dose (2.5 mg) and daily oral doses for one week of Brc to normal male volunteers.
• Measurement of plasma concentrations of dopamine (DA), norepinephrine (NE), and epinephrine (E) at various time points.
• Monitoring of serum prolactin (Prl), luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, and dihydrotestosterone levels.
• Assessment of plasma catecholamine responses to standing and incidence of orthostatic hypotension.

Main Results:

• A single 2.5 mg oral dose of Brc caused significant, comparable decreases in resting supine plasma DA, NE, and E levels (p < 0.001).
• Brc's suppressive effect on plasma catecholamines was rapid and shorter in duration than its effect on serum prolactin.
• Daily Brc administration for one week did not alter catecholamine levels after 4 hours, and subsequent doses showed similar suppressive effects.
• Brc did not inhibit catecholamine responses to standing, though orthostatic hypotension occurred occasionally.
• Basal serum levels of LH, FSH, testosterone, and dihydrotestosterone remained unaffected by Brc.

Conclusions:

• Bromocriptine administration effectively suppresses peripheral sympathetic nerve ending and adrenal medulla release of dopamine, norepinephrine, and epinephrine.
• The findings suggest Brc acts partly via presynaptic catecholamine receptors in the brain.
• The suppressive effect of Brc on plasma catecholamines may serve as a valuable test for assessing normal presynaptic catecholamine mechanisms.