Mepyramine inhibits platelet activating factor-induced rabbit platelet aggregation: role of intracellular histamine
Abstract
AIM: To study the possible role of intracellular histamine (HA) in platelet
activating factor (PAF)-induced platelet activation.
METHODS: Washed rabbit platelet suspension was used to test the inhibitory effect
of mepyramine (Mep, an H1 receptor antagonist) on PAF-induced platelet
aggregation. The thromboxane B2 (TXB2) generation was measured by
radioimmunoassay and the intracellular calcium ([Ca2+]i) concentration was
determined by the specific fluorescence indicator Fura-2.
RESULTS: Mep > 100 mumol.L-1 generated a concentration-dependent inhibition on
PAF-induced aggregation, with an IC50 value of 162 (95% confidence limits:
114-232 mumol.L-1). Cimetidine, an H2 receptor antagonist, even up to 400
mumol.L-1 had no effect on it. Exogenous HA (10 mumol.L-1) and H1 receptor
agonist, 2-thiazolylethylamine had no energetic effect.
alpha-Fluoromethylhistidine, an inhibitor of histidine decarboxylase, did not
inhibit platelet responses. However, in platelets permeabilized with saponin
(8-10 mg.L-1), exogenous HA attenuated the inhibitory effect of Mep to about 50%
at a concentration of 50 mumol.L-1. Preincubation of platelets with Mep (100 or
200 mumol.L-1) resulted in an inhibition on TXB2 generation and [Ca2+]i elevation
induced by PAF.
CONCLUSION: Platelets activated by PAF is associated with an intracellular HA
synthesis and release via a common pathway of TXB2 generation and the rise of
[Ca2+]i.
Keywords:
activating factor (PAF)-induced platelet activation.
METHODS: Washed rabbit platelet suspension was used to test the inhibitory effect
of mepyramine (Mep, an H1 receptor antagonist) on PAF-induced platelet
aggregation. The thromboxane B2 (TXB2) generation was measured by
radioimmunoassay and the intracellular calcium ([Ca2+]i) concentration was
determined by the specific fluorescence indicator Fura-2.
RESULTS: Mep > 100 mumol.L-1 generated a concentration-dependent inhibition on
PAF-induced aggregation, with an IC50 value of 162 (95% confidence limits:
114-232 mumol.L-1). Cimetidine, an H2 receptor antagonist, even up to 400
mumol.L-1 had no effect on it. Exogenous HA (10 mumol.L-1) and H1 receptor
agonist, 2-thiazolylethylamine had no energetic effect.
alpha-Fluoromethylhistidine, an inhibitor of histidine decarboxylase, did not
inhibit platelet responses. However, in platelets permeabilized with saponin
(8-10 mg.L-1), exogenous HA attenuated the inhibitory effect of Mep to about 50%
at a concentration of 50 mumol.L-1. Preincubation of platelets with Mep (100 or
200 mumol.L-1) resulted in an inhibition on TXB2 generation and [Ca2+]i elevation
induced by PAF.
CONCLUSION: Platelets activated by PAF is associated with an intracellular HA
synthesis and release via a common pathway of TXB2 generation and the rise of
[Ca2+]i.