Aqueous humor adrenomedullin levels differ in patients with different types of glaucoma

Adrenomedullin is a multifunctional 52 amino acid large peptide. Recent studies have reported that it is expressed in the iris-ciliary body in the eye and that it decreases intraocular pressure (IOP) by increasing outflow facility via specific adrenomedullin receptors, suggesting a role for this peptide in controlling IOP. In the present study, we aimed to explore clinically the possible involvement of adrenomedullin in the pathophysiology of glaucoma.

Reverse-phase high-performance liquid chromatography was used to determine the aqueous humor adrenomedullin levels in 41 patients (41 eyes) undergoing elective surgery for a variety of ocular diseases in the Research Hospital of Inönü University Medical Faculty between 1999 and 2000. The ocular diseases of the patients included primary open-angle glaucoma (POAG, n = 16), neovascular glaucoma (NG, n = 11), and cataract (n = 14). The study was an open trial with purposive sampling. Aqueous humor samples were taken by paracentesis. Mann-Whitney U-test was used in the statistical analysis and P <.05 was considered as significant. Results were expressed as mean +/- SE.

The mean age and sex distribution between groups were comparable. Mean adrenomedullin levels in patients with POAG (22.3 +/- 0.6 pmol/L) were significantly higher than those in patients with NG (5.6 +/- 0.2, pmol/L; P <.001) and cataract (11.9 +/- 0.5, pmol/L; P <.001). On the other hand, the mean aqueous humor adrenomedullin levels in patients with NG were significantly (P <.001) lower than those in cataract patients.

This first clinical in vivo study on aqueous humor adrenomedullin levels showed that this peptide may be involved in the pathophysiology of glaucoma. Increased aqueous humor adrenomedullin levels in patients with POAG may indicate a compensatory defense response against increased IOP to slow the formation and progression of a vicious cycle. On the other hand, there may be deficient production of the peptide in patients with NG, or adrenomedullin-producing cells may be lost because of very high IOP during the course of the disease. The control of adrenomedullin levels in the eye might be a target that could be considered in the therapeutic strategies for glaucoma. Further studies in this respect are needed.