Histamine uptake in pig platelets and isolated dense granules

Area of Science:

• Hematology
• Biochemistry
• Pharmacology

Background:

• Platelets store histamine in amine-storage organelles.
• Histamine uptake by intact platelets is minimal compared to serotonin.
• Pig platelets exhibit higher plasma histamine levels than other species.

Purpose of the Study:

• To investigate the mechanism and origin of histamine storage in pig platelets.
• To determine if histamine and serotonin storage pathways are interconnected.
• To elucidate the role of megakaryocytes in platelet histamine content.

Main Methods:

• Measuring amine uptake in intact platelets and isolated storage organelles.
• Utilizing radiolabeled histamine (3H-amine) and serotonin (14C-serotonin).
• Assessing amine release induced by thrombin and enzyme activity (histidine decarboxylase).

Main Results:

• Intact platelets accumulate histamine poorly; isolated organelles show slow, ATP-dependent uptake.
• Thrombin releases most endogenous histamine but little newly absorbed amine.
• Histamine and serotonin storage appear independent, with no observed cross-inhibition.

Conclusions:

• Platelet histamine is likely acquired during megakaryocyte development, not synthesized or primarily taken up by mature platelets.
• The slow uptake and independent storage suggest a distinct mechanism for histamine accumulation.
• Megakaryocyte origin is the probable source for platelet histamine in pigs.