The effect of acute hyperglycaemia on the retinal circulation of the normal cat

The retinal microcirculation of anaesthetised normal cats was studied during hyperglycaemia (15 to 55 mmol/l) induced by intravenous infusion of glucose, using high speed cine fluorescence angiography. Saline (0.150 mmol/l) was infused as a control for the volume effect of glucose solution and equiosmolar mannitol was infused as a control for the osmotic effect. The mean retinal arteriolar inflow rate increased from 34 +/- 1 mm/sec to 41 +/- 4 mm/sec during glucose infusion, and from 46 +/- 1 mm/sec to 56 +/- 3 mm/sec during mannitol infusion. The blood pressure similarly increased from 105 +/- 5 mmHg to 125 +/- 2 mmHg during glucose infusion and from 110 +/- 7 mmHg to 129 +/- 1 mmHg during mannitol infusion. During mannitol infusion the increased inflow was accompanied by a reduction in the arteriolar width so that the volume flow remained unchanged. During glucose infusion this constriction did not occur, resulting in a significantly increased volume of retinal blood flow (9 +/- 1 microliter/min to 12 +/- 1 microliter/min).