THE EFFECT OF SYSTEMIC NITRIC-OXIDE SYNTHASE INHIBITION ON OCULAR FUNDUS PULSATIONS IN MAN

There is experimental evidence that endothelium derived nitric oxide i s involved in the regulation of ocular vascular tone. The purpose of t his study was to investigate the effects of NO-synthase inhibition by N-monomethyl-L-arginine (L-NMMA) on ocular fundus pulsations in young healthy volunteers. Three milligrams per kilograms L-NMMA were adminis tered i.v. over 5 minutes. Protocol 1:Measurements of blood pressure, pulse rate, fundus pulsation amplitude, NO-exhalation, and cardiac out put were performed at baseline and 10, 30, 60, 90, 150, and 300 minute s after L-NMMA infusion (n = 8). Fundus pulsation amplitude, which has been shown to estimate the pulsatile component of the choroidal blood flow, was recorded with a recently developed laser interferometer. Pr otocol 2: Measurements of blood pressure, pulse rate, fundus pulsation amplitude, NO-exhalation, and blood now velocity in the ophthalmic ar tery were performed in a randomized, placebo controlled cross over stu dy (n = 10). Ten minutes after L-NMMA administration fundus pulsation amplitude decreased by 23 +/- 2% (protocol 1) and 19 +/- 1% (protocol 2, P < 0.01 each), cardiac output by 12 +/- 2% (P < 0.01), and exhaled NO by 55 +/- 6% (protocol 1) and 41 +/- 6% (protocol 2, P < 0.01 each ). All parameters returned to baseline values within the 300 minutes o bservation period, with a faster recovery of fundus pulsation amplitud e than of cardiac output and exhaled NO. Blood pressure, pulse rate, a nd ophthalmic artery blood now velocity showed only minor changes duri ng and after administration of L-NMMA. Our results suggest that system ic NO-synthase inhibition reduces pulsatile choroidal and most likely total choroidal blood flow in humans. The recovery of vascular tone in choroidal vessels seems to be different from the cardiovascular respo nse. Our findings indicate that reduced fundus pulsations after L-NNMA are caused by systemic factors as well as by local reactions of the c horoidal vasculature. (C) 1997 Academic Press Limited.