Alpha adrenoceptor blockade with oral prazosin.

Area of Science:

• Pharmacology
• Cardiovascular Physiology

Background:

• Alpha-adrenoceptors play a crucial role in regulating blood pressure.
• Prazosin is an alpha-adrenoceptor antagonist used clinically.

Purpose of the Study:

• To assess the duration and extent of alpha-adrenoceptor blockade induced by oral prazosin.
• To investigate the relationship between prazosin plasma concentration and its pharmacological effect.

Main Methods:

• Five healthy subjects received placebo or 5 mg oral prazosin.
• Phenylephrine infusion was used to assess alpha-adrenoceptor blockade.
• Blood pressure and drug-sensitivity ratios were measured over time.

Main Results:

• Prazosin significantly reduced systolic blood pressure response to phenylephrine.
• Alpha-adrenoceptor blockade persisted for at least 7 hours post-prazosin administration.
• No correlation was found between prazosin plasma concentration and the blockade effect.

Conclusions:

• Oral prazosin provides a sustained blockade of alpha-adrenoceptors.
• The pharmacological effect of prazosin is not directly predicted by its plasma concentration.