Platelet aggregation by rat liver. Evidence for ADP as major factor

Area of Science:

• Biochemistry
• Hematology
• Physiology

Background:

• Platelet aggregation is a key process in hemostasis and thrombosis.
• Tissue damage can release substances that influence platelet activity.

Purpose of the Study:

• To identify the substance in liver and other tissues responsible for inducing platelet aggregation in vitro.
• To characterize the properties of this aggregation-inducing agent.

Main Methods:

• Preparation of rat liver ultrafiltrates.
• Charcoal adsorption, dialysis, and membrane filtration to purify the active substance.
• Thermostability, pronase digestion, and acid/alkali resistance assays.
• Apyrase incubation to assess activity loss.

Main Results:

• The active substance in liver ultrafiltrates demonstrated properties consistent with adenosine diphosphate (ADP).
• The agent was dialyzable, filterable (MW > 1000), and absorbed on charcoal.
• It was thermostable in ultrafiltrates but thermolabile in homogenates, suggesting enzyme inactivation.
• Activity was resistant to pronase, acid, and alkali, but lost upon apyrase treatment.
• Direct ADP detection was limited by assay sensitivity, yet aggregation occurred.

Conclusions:

• The primary platelet-aggregating agent in rat liver ultrafiltrates is likely adenosine diphosphate (ADP).
• Understanding ADP release from cells during injury may elucidate thrombosis mechanisms.