Role of nitric oxide in optic nerve head blood flow regulation during an experimental increase in intraocular pressure in healthy humans.
The present study set out to investigate whether nitric oxide, a potent vasodilator, is involved in the regulatory processes in optic nerve head blood flow during an experimental increase in intraocular pressure (IOP). The study was conducted in a randomized, double-masked, placebo-controlled, three way cross-over design. 12 healthy subjects were scheduled to receive either L-NMMA (an unspecific nitric oxide synthase inhibitor), phenylephrine (an α-adrenoceptor agonist) or placebo on three different study days. Optic nerve head blood flow was measured using laser Doppler flowmetry and IOP was increased stepwise with a suction cup. Mean arterial pressure (MAP) and IOP were measured non-invasively and ocular perfusion pressure (OPP) was calculated as OPP = 2/3 MAP-IOP. Administration of L-NMMA and phenylephrine significantly increased MAP and therefore OPP at rest (p < 0.01). L-NMMA significantly reduced baseline blood flow in the optic nerve head (p < 0.01). Application of the suction cup induced a significant increase in IOP and a decrease in OPP (p < 0.01). During the stepwise increase in IOP, some autoregulatory potential was observed until OPP decreased approximately -30% below baseline. None of the administered substances had an effect on this autoregulatory behavior (p = 0.49). The results of the present study confirm that the human optic nerve head shows some regulatory capacity during a decrease in OPP. Nitric oxide is involved in the regulation of basal vascular tone in the optic nerve head but does not seem to be involved in the regulatory mechanisms during an acute increase in IOP in young healthy subjects.
Department of Clinical Pharmacology, Medical University of Vienna, Austria; Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria.
Doreen
D
Schmidl
Agnes
A
Boltz
Semira
S
Kaya
Stefan
S
Palkovits
Reinhard
R
Told
Katarzyna Jadwiga
KJ
Napora
Alina Popa
AP
Cherecheanu
René Marcel
RM
Werkmeister
Gerhard
G
Garhofer
Leopold
L
Schmetterer
D000328:Adult; D018592:Cross-Over Studies; D004311:Double-Blind Method; D045462:Endothelium-Dependent Relaxing Factors / Q000494:pharmacology; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D017078:Laser-Doppler Flowmetry; D008297:Male; D009569:Nitric Oxide / Q000494:pharmacology*; D009798:Ocular Hypertension / Q000503:physiopathology*; D009898:Optic Disk / Q000098:blood supply*; D012016:Reference Values; D012039:Regional Blood Flow / Q000187:drug effects*; D014065:Tonometry, Ocular
D045462:Endothelium-Dependent Relaxing Factors; D009569:Nitric Oxide
GON; LDF; NO; NOS; ONH; ONHBF; OPP; autoregulation; glaucomatous optic neuropathy; intraocular pressure; laser Doppler flowmetry; nitric oxide; nitric oxide synthase; ocular perfusion pressure; optic nerve head; optic nerve head blood flow