L-arginine and L-nitroarginine methylester effects on vasomotion in isolated rabbit eyes.
OBJECTIVE
Although nitric oxide (NO) has been shown to be essential for maintaining the basal blood flow in the retina and optic nerve head, its exact role in vasomotion is still controversial. This study investigated L-arginine (L-Arg) and N-nitro-L-arginine methylester (L-NAME) effects on vascular reactivity in a model of isolated rabbit eye.


METHODS
Rabbit external ophthalmic arteries (n = 12) in a head-mounted preparation were cannulated and perfused with warmed Tyrode solution. The effect of intraluminal pressure as a measure of total vascular resistance was assessed. Response curves to intra-arterial injections of 3 growing concentrations of L-Arg (n = 6) and L-NAME (n = 6) were obtained.


RESULTS
Without any drug administration, spontaneous oscillations were observed in all the models. L-Arg (NO precursor) induced vasodilation and decreased both frequency and amplitude of the periodic oscillations. L-NAME (NO synthase inhibitor) produced a strong vasoconstrictor tone and stimulated vasomotion, causing a faster rate of pulsatility.


CONCLUSIONS
L-Arg and L-NAME acted as modulators of ocular vascular tone. L-Arg elicited vasodilation and decreased vasomotion while L-NAME produced a strong vasoconstrictor tone and caused a faster rate of pulsatility. These findings justify the need to investigate NO precursors and antagonists as possible alternative therapeutics in vascular eye diseases.
Delgado
E
E
Departamento de Clínica, Centro de Investigação Interdisciplinar em Sanidade Animal, Faculty of Veterinary Medicine, Alameda da Universidade Técnica, Lisbon, Portugal. esmeralda@fmv.utl.pt
Marques-Neves
C
C
Rocha
I
I
Sales-Luís
J
J
Silva-Carvalho
L
L
D000818:Animals; D001120:Arginine / Q000008:administration & dosage / Q000494:pharmacology*; D001783:Blood Flow Velocity; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D007269:Injections, Intra-Arterial; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D019331:NG-Nitroarginine Methyl Ester / Q000008:administration & dosage / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009880:Ophthalmic Artery / Q000187:drug effects / Q000502:physiology*; D011673:Pulsatile Flow; D011817:Rabbits; D012039:Regional Blood Flow; D014661:Vasoconstriction / Q000502:physiology*; D014664:Vasodilation / Q000502:physiology*
D004791:Enzyme Inhibitors; D001120:Arginine; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester