A novel platelet-activating protein derived from rat submandibular glands

Area of Science:

• Biochemistry
• Hematology
• Physiology

Background:

• Platelet-activating factor (PAF) is a key substance involved in platelet aggregation and secretion.
• Naturally occurring substances that activate platelets are of significant research interest.

Purpose of the Study:

• To isolate and characterize a novel platelet-activating substance from rat submandibular salivary glands.
• To compare the properties of this new substance with known platelet-activating factors and stimulants.

Main Methods:

• Isolation and partial purification of RS-PAP from rat salivary glands.
• In vitro activation assays using washed, radiolabeled platelets from rats, rabbits, and humans.
• Comparative studies with 1-O-alkyl-2-acetyl-sn-glycero-3-phosphorylcholine (AGEPC) and collagen.
• Enzyme inhibition assays and heat inactivation.
• Gel filtration for molecular weight determination.

Main Results:

• RS-PAP induced a dose-related activation of platelets from multiple mammalian species.
• Platelet activation by RS-PAP required extracellular calcium and was not affected by indomethacin.
• RS-PAP activity was resistant to inhibitors of AGEPC degradation but was inactivated by heat, trypsin, and phospholipid extraction.
• Gel filtration estimated the molecular weight of RS-PAP to be 22,000-25,000 daltons.

Conclusions:

• RS-PAP is a novel platelet-stimulating protein, distinct from phospholipid PAFs.
• This protein activates platelets from various mammalian species.
• RS-PAP represents a new class of platelet-activating agents with potential physiological roles.