Possible role for nitric oxide releasing nerves in the regulation of ocular blood flow in the rat

AIM—To investigate the role of nitrergic nerves in the regulation of ocular blood flow.
METHODS—Conscious, lightly restrained rats were treated with either the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI), or the non-selective inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), and ocular blood flow was measured ex vivo from tissue samples, using the fully quantitative [14C]-iodoantipyrine technique.
RESULTS—In the peripheral circulation, L-NAME produced an increase in arterial blood pressure (+22%) while 7-NI had no effect. In contrast, both 7-NI and L-NAME produced significant decreases in ocular blood flow (−31% and −59% respectively). The ocular vascular resistance calculated from ocular blood flow and mean arterial blood pressure increased by 29% following 7-NI, but by 130% following L-NAME.
CONCLUSIONS—Nitric oxide releasing neurons may play an important contributory role in regulating ocular blood flow.

Keywords: nitric oxide; neuronal nitric oxide synthase; 7-nitroindazole; NG-nitro-L-arginine methyl ester; ocular blood flow