Naloxone attenuates the hypotension induced by Hageman factor

Area of Science:

• Pharmacology
• Physiology
• Biochemistry

Background:

• The Hageman factor (HF) system, also known as the contact activation system, plays a role in inflammation and coagulation.
• Hypotension, or low blood pressure, can be induced by various mediators, including kinins and products of HF activation.
• The role of endogenous opioid peptides in mediating hypotension induced by HF activation is not fully understood.

Purpose of the Study:

• To investigate the role of endogenous opioid peptides in hypotension induced by Hageman factor activation.
• To determine if naloxone, an opiate antagonist, can attenuate hypotension elicited by an active Hageman factor fragment (Hff).
• To assess the specificity of naloxone's effect by comparing it to hypotension induced by other vasoactive agents.

Main Methods:

• Intravenous administration of an active Hageman factor fragment (Hff) to pentobarbital-anesthetized rats.
• Measurement of blood pressure changes following Hff administration.
• Administration of naloxone, an opiate antagonist, before Hff to assess its effect on hypotension.
• Comparison of naloxone's effect on Hff-induced hypotension with its effect on hypotension induced by rat urinary kallikrein, bradykinin, and nitroglycerin.

Main Results:

• Intravenous administration of Hff induced significant hypotension in rats.
• Naloxone significantly attenuated the hypotension induced by Hff.
• Naloxone did not significantly alter the hypotension elicited by rat urinary kallikrein, bradykinin, or nitroglycerin, indicating specificity.
• These findings suggest a role for opioid pathways in mediating Hageman factor-induced hypotension.

Conclusions:

• The hypotension induced by Hageman factor activation in rats is specifically mediated, at least in part, by opioid pathways.
• Contact activation of endogenous Hageman factor may lead to the generation of vasoactive opioid peptides.
• These opioid peptides are likely derived from circulating large molecular weight precursors and contribute to blood pressure regulation.