Molecular biological and functional studies on prostanoid receptor distribution in human ocular tissues in situ and in vitro have shown that trabecular meshwork cells express FP receptors,
26 lens epithelium expresses EP
4 and FP receptors,
16 and ciliary epithelial and ciliary muscle cells express EP
2, EP
4, and FP receptors.
17 18 19 20 21 27 These isolated data are largely confirmed by the findings of the present study. However, it has to be taken into account that the literature is somewhat confusing regarding the EP
2 receptor’s nomenclature, because before 1995, when the human EP
2 receptor was cloned, the cloned EP
4 receptor was misclassified as the EP
2 receptor.
28 Ligand binding and quantitative autoradiographic visualization of FP receptors yielded the highest receptor concentration in the longitudinal ciliary muscle, the iris sphincter muscle, and the retina of human eyes,
29 which is partly in agreement with the present findings; however, in this study, high concentrations of FP receptors were mainly detected in the circular portion of the ciliary muscle and also in the corneal and ciliary epithelium. In situ hybridization revealed the presence of high levels of EP
1 receptor mRNA in blood vessels of the iris, ciliary body, and choroid, in the iris sphincter, ciliary muscle, and retina (photoreceptors, inner and outer nuclear layers, ganglion cells). FP receptor mRNA was predominantly present in the circular portion of the ciliary muscle and in the ciliary stroma, iris vasculature, and iris sphincter, but was absent in the retina and choroidal vasculature.
22 Apart from the absence of signals for FP receptor mRNA in retina and choroid, these data are again in good agreement with the findings of receptor distribution in the present study.