The mechanism and change in the optic nerve head (ONH) circulation in rabbits after glucose loading

Purpose. To assess the influence of the blood glucose level on ocular capil lary circulation, we induced clinically significant hyperglycemia (200-300 mg/dl) in rabbits and investigated the changes in the optic nerve head (ONH ) circulation. Methods. Hyperglycemia was induced by injection of glucose (5.6 mmol/kg) in to an auricular vein of healthy albino rabbits and changes in the ONH circu lation were measured by the laser speckle method. In order to examine the r ole of nitric oxide (NO), glucose was administered after intravenous inject ion of an NO synthetase inhibitor (N-G nitro-L-arginine methyl ester, L-NAM E, 1 mg/kg), then changes in the ONH circulation were measured. Results. The blood glucose level reached a peak at 30 min after glucose loa ding and returned to its initial level by 2 hours. ONH circulation showed a 60% increase compared with its initial level at 15 min after glucose loadi ng and subsequently remained almost unchanged throughout the 2-hour observa tion period. There were no significant changes of the blood pressure, heart rate, or intraocular pressure. The glucose-induced increase of ONH circula tion was completely inhibited by pretreatment with L-NAME. Conclusions. ONH circulation was increased by administration of glucose to healthy rabbits. A high blood glucose level seems to promote ocular capilla ry circulation and NO as well as insulin appear to have a role in this proc ess.