Nifedipine and alpha adrenoceptor antagonism

Area of Science:

• Pharmacology
• Cardiovascular Physiology

Background:

• Nifedipine is a calcium channel blocker with known hypotensive effects.
• Alpha-2 adrenergic receptors play a role in regulating blood pressure.

Purpose of the Study:

• To investigate the effects of nifedipine on pressor responses to specific agonists in humans.
• To determine if nifedipine acts as a selective alpha-2 adrenergic antagonist in humans.

Main Methods:

• Comparison of pressor dose-response curves of methoxamine, alpha-methylnorepinephrine, and angiotensin II with nifedipine versus placebo.
• Administration of agonists and nifedipine or placebo to normal subjects.

Main Results:

• Nifedipine shifted the pressor dose-response curves for all three agonists to the right.
• The magnitude of the shift (dose ratios) was similar for all tested agonists.
• Nifedipine's effect was not selective for alpha-2 adrenergic antagonism in humans.

Conclusions:

• Nifedipine is not a selective alpha-2 adrenergic antagonist in humans.
• Nifedipine may contribute to blood pressure reduction through antagonism of norepinephrine and angiotensin II.
• Findings contrast with observations in animal models regarding nifedipine's selectivity.