Sir,
We thank Dr Masood for his useful comments. The mechanism he suggested is tempting, however, it is speculative. It should be emphasized that at the time the patient received metoprolol tartrate he was no longer on timolol. Both beta1- and beta2-adrenergic receptors have been identified in the human iris and ciliary body.1 Activation of beta2 receptors increases the formation of cyclic adenosine monophosphate and stimulation of Na+, K+, Cl− cotransport in the foetal nonpigmented ciliary epithelium.2 Metoprolol may as well have an indirect effect on the Na–K pump via adrenergic receptors. This may either result in changes in aqueous production or in concentration of inflammatory mediators in the anterior segment and explains its clinical effect in the specific individual with type A personality. It should be clinically determined if metoprolol has a similar effect on different individuals and in which dosage. The drug may have different activities in different concentrations. The molecular mechanism of metoprolol effect should be evaluated also in cell cultures. Our study is intended to provoke research in these directions.
References
Wax MB, Molinoff PB . Distribution and properties of beta-adrenergic receptors in human iris-ciliary body. Invest Ophthalmol Vis Sci 1987; 28: 420–430.
Crook RB, Riese K . Beta-adrenergic stimulation of of Na+, K+, Cl− cotransport in the fetal non-pigmented ciliary epithelial cells. Invest Ophthalmol Vis Sci 1996; 37: 1047–1057.
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Kassif, Y., Rehany, U. & Rumelt, S. Metoprolol responding uveitis: reply. Eye 19, 720 (2005). https://doi.org/10.1038/sj.eye.6701625
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DOI: https://doi.org/10.1038/sj.eye.6701625