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Histamine H2 receptor-mediated cyclic AMP formation in human platelets
Abstract:
The influence of histamine on the level of cyclic AMP was studied in human platelets. A dose-related accumulation of cyclic AMP was obtained, culminating at about 10 microM of histamine. The response was blocked by the H2 antagonist cimetidine, but neither by H1 antagonists nor by alpha- or beta-adrenergic antagonists. The results suggest that histamine causes an accumulation of cyclic AMP in human platelets by stimulation of H2 receptors. Cyclic AMP accumulation is supposed to be associated with a depression of the platelet function, and a reduced platelet release reaction was actually demonstrated by our results.
Insights
Histamine stimulates H2 receptors in human platelets, increasing cyclic AMP levels and reducing platelet function. This finding highlights a specific mechanism for controlling platelet activity.
Area of Science:
- Biochemistry
- Pharmacology
- Hematology
Background:
- Platelets play a crucial role in hemostasis and thrombosis.
- Cyclic AMP (cAMP) is a key intracellular second messenger regulating platelet activation.
- Histamine is a biogenic amine with diverse physiological roles.
Purpose of the Study:
- To investigate the effect of histamine on cyclic AMP (cAMP) levels in human platelets.
- To determine the specific histamine receptor subtype involved in this effect.
- To assess the functional consequences of histamine-induced cAMP accumulation on platelet activity.
Main Methods:
- Human platelets were incubated with varying concentrations of histamine.
- Cyclic AMP (cAMP) levels were measured using established biochemical assays.
- Pharmacological agents, including H1 and H2 antagonists and adrenergic antagonists, were used to identify receptor involvement.
- Platelet release reactions were assessed to evaluate functional changes.
Main Results:
- Histamine induced a dose-dependent accumulation of cyclic AMP (cAMP) in human platelets, peaking at approximately 10 microM.
- The histamine-induced cAMP increase was specifically blocked by the H2 receptor antagonist cimetidine.
- Neither H1 antagonists nor alpha- or beta-adrenergic antagonists affected the histamine response.
- A reduction in platelet release reaction was observed, consistent with the functional role of cAMP.
Conclusions:
- Histamine stimulates cyclic AMP (cAMP) accumulation in human platelets primarily through the activation of H2 receptors.
- This histamine-mediated cAMP increase is associated with a depression of platelet function, specifically reducing the platelet release reaction.
- The findings identify a novel signaling pathway involving histamine and H2 receptors that modulates human platelet activity.