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L. Choritz, M. Machert, N. Pfeiffer, H. Thieme; Endothelin-1 Concentrations in Aqueous Humor but Not in Blood Plasma Correlate With IOP. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4862.
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Endothelin-1 (ET-1) has been found to be increased in the aqueous humor of glaucoma patients compared to cataract patients and is suspected to directly influence intraocular pressure (IOP) through inducing contractions in both trabecular meshwork (TM) and ciliary muscle (CM). However, it has never been examined, whether ET-1 concentrations in aqueous humor actually correlate with IOP. The aim of this study was to determine whether ET-1 concentrations in aqueous humor and blood plasma of cataract and glaucoma patients do correlate with IOP.
Aqueous humor as well as blood samples from patients with either cataract (control group, n=38), POAG (n=35) or PEXG (n=21) and with no other ocular or systemic disease were collected during routine cataract surgery or trabeculectomy. ET-1 concentration was determined using a highly specific ET-1 ELISA Kit that does not cross-react with other ET isoforms or precursors. IOP was measured pre-operatively by standard Goldmann applanation tonometry. All statistical analysis was performed using SPSS 16.
Both IOP and ET-1 concentration in aqueous humor were significantly increased in the POAG (23.4 ± 6.8 mmHg, 5.9 ± 2.9 pg/ml) and PEXG (24.3 ± 8.8 mmHg, 7.7 ± 2.1 pg/ml) groups compared to the cataract group (15.0 ± 2.9 mmHg, 4.3 ± 2.4 pg/ml), whereas no such difference could be detected for plasma ET-1 concentrations (4.7 ± 3.2 and 5.0 ± 2.0 pg/ml in POAG and PEXG versus 5.7 ± 5.2 pg/ml in cataract). While IOP and ET-1 in aqueous humor were significantly correlated (R= 0.394, R²=0.155, p<0.001), no correlation was found between IOP and ET-1 in blood plasma (R=-0.145, p=0.18) or between ET-1 in aqueous humor and ET-1 in plasma (R=-0.004, p=0.97). No statistical differences between the patient groups were found regarding age, gender or study eye.
Statistically, 15.5% of the variation in IOP in the entire study population was explained by the ET-1 concentration in aqueous humor in this investigation. While this indicates a direct link between IOP and ET-1, the large variance in both variables does not allow prediction of either variable based on the other. The increased ET-1 concentrations in the PEX-Glaucoma group indicate that ET-1 increase in aqueous humor may in fact be secondary to IOP increase. Current theories about the role of of ET-1 in ocular physiology and pathophysiology need to be evaluated critically and further studies on this issue are warranted.
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