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Characterization of specific binding sites for PAF in the iris and ciliary body of rabbit
M T Domingo1, P E Chabrier, J L Van Delft
1Institut Henri Beaufour LES ULIS, France.
Abstract:
The protective effect exerted by BN 52021 a specific PAF-receptor antagonist in experimentally induced ocular inflammatory disorders led us to investigate the possible presence of specific receptors for PAF in rabbit iris and ciliary body. Two classes of PAF binding sites were found in isolated iris and ciliary process of pigmented rabbit eyes: a high affinity site Kd1 congruent to 4.9 +/- 0.47 nM, Bmax1 congruent to 3.17 +/- 0.50 pmoles/mg protein, a low affinity sites Kd2 congruent to 11.6 +/- 0.33 nM, Bmax2 congruent to 12.46 +/- 2.3 pmoles/mg protein for iris. The specific binding was not affected by lyso-PAF the biologically inactive precursor and metabolite of PAF, up to 10(-6) M; inhibition by unlabelled PAF demonstrated a biphasic curve partially antagonized by BN 52021. The present results demonstrate the presence of specific binding sites for PAF in rabbit eyes which could mediate the action of this mediator in eye inflammatory processes and explain the protective effect observed with BN 52021.
Insights
Researchers found specific platelet-activating factor (PAF) binding sites in rabbit eyes, explaining how the drug BN 52021 reduces ocular inflammation by blocking these receptors.
Area of Science:
- Ophthalmology
- Immunology
- Pharmacology
Background:
- Platelet-activating factor (PAF) is implicated in ocular inflammatory disorders.
- BN 52021, a PAF-receptor antagonist, demonstrates protective effects in experimental ocular inflammation.
Purpose of the Study:
- To investigate the presence and characteristics of specific PAF receptors in rabbit iris and ciliary body.
- To understand the mechanism of action for BN 52021 in ocular inflammation.
Main Methods:
- Radioligand binding assays using [3H]-PAF on isolated rabbit iris and ciliary processes.
- Competition binding studies with unlabeled PAF and BN 52021.
Main Results:
- Two classes of specific PAF binding sites were identified in rabbit iris and ciliary processes: high-affinity (Kd1 ≈ 4.9 nM) and low-affinity (Kd2 ≈ 11.6 nM).
- Binding was specific for PAF and not affected by lyso-PAF.
- BN 52021 partially antagonized PAF binding, indicating interaction with the receptor.
Conclusions:
- Specific binding sites for PAF exist in the rabbit eye, particularly in the iris and ciliary body.
- These receptors likely mediate PAF's actions in ocular inflammatory processes.
- The findings support the therapeutic potential of PAF antagonists like BN 52021 for treating eye inflammation.