Retinal blood flow during hyperglycemia. A laser Doppler velocimetry study

The effect of different rates of glucose infusion on the retinal circulation was studied in Gottingen breed minipigs. Seven minipigs were made hyperglycemic rapidly with an intravenous bolus injection of 50% dextrose, after which a slow dextrose infusion maintained hyperglycemia for 60 minutes. Seven minipigs were more gradually made hyperglycemic over 60 minutes with a slow intravenous infusion of 50% dextrose, and a further seven had a control infusion of urea of equal volume and osmolality over 60 minutes. Retinal blood flow (RBF) was determined from the maximum (centerline) velocity of the blood (Vmax) (determined by bidirectional laser doppler velocimetry) and the vessel diameter (D) (determined from monochromatic fundus photographs). Measurements were made in a single temporal retinal vein of each animal at baseline, during, and after each of the infusions. Plasma glucose rose from 6.1 +/- 0.5-25.3 +/- 1.5 mM (mean +/- standard error) during the bolus infusion and from 6.4 +/- 0.7-22.0 +/- 0.7 mM during the slow infusion. The bolus and the slow glucose infusions both produced large increases in RBF (63% and 62%, respectively) which were mainly attributable to increases in Vmax. The urea infusion had no significant effect on RBF, Vmax, or D. The ocular perfusion pressure rose slowly and was significantly elevated after 60 minutes of slow glucose infusion but not after the urea infusion.