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DL Geiger, DE Potter; Natriuretic Peptides Inhibit Norepinephrine Release in the Iris Ciliary Body . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4115.
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Purpose: Preliminary studies in this laboratory have shown that certain drugs which lower IOP also increase atrial natriuretic peptide (ANP) levels in aqueous humor. Therefore, the aim of this study was to determine whether natriuretic peptides (ANP/CNP) modulate ocular hydrodynamics, in part, by regulating activity of the sympathetic nervous system. Methods: Norepinephrine (NE) release from iris-ciliary bodies (ICBs) of New Zealand White (NZW) rabbits was determined in the presence of ANP and CNP. The ICBs were incubated for 1 hour in perfusion medium (EBSS), containing indomethacin and 3H-NE. After loading the ICBs with 3H-NE, tissues were washed, perfused and subjected to multiple field stimulations by electrical current in the absence (control) and presence of increasing concentrations of ANP or CNP. Desipramine was added to both reservoirs containing EBSS. The tissues were stimulated at predetermined time intervals and samples were collected using a fraction collector. Varying concentrations (1 nM, 10 nM, and 100 nM) of ANP and CNP were added sequentially to the perfusion medium reservoirs. The 3H-NE released into the perfusate was quantified using a scintillation counter. Results: Both ANP and CNP caused initial concentration-dependent inhibition of the release of 3H-NE from the ICB of NZW rabbits. The range of responses (percent of control) for ANP and CNP, respectively, were: 1 nM, 81-84%; 10 nM, 59-65%; and 100 nM, 77-68%. Conclusion: These results indicate that natriuretic peptides regulate the release of norepinephrine from the sympathetic nerves in the ICB of the NZW rabbit. Inhibition of the release of norepinephrine may be one of the mechanisms by which natriuretic peptides lower IOP. Therefore, drugs that enhance natriuretic peptide activity in the anterior segment could prove to be potential therapies for glaucoma.
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