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SUMMARY1. The mean velocities at which granulocytes roll along the walls of small venules have been related to their mean blood flow velocities in preparations of hamster cheek pouch and mouse mesentery. In animals anaesthetized with Nembutal, 30-200 ,tm venules were observed microscopically and the movement of rolling granulocytes quantitated on films. Apparent mean blood flow velocity was determined from films of embolizing platelet thrombi.2. In four venules the velocity distribution of about 100 rolling cells was almost symmetrical about the mode, with a small proportion moving at up to three times the mode velocity. Therefore, the mean and mode velocities were very similar.3. In two mesenteric and two cheek-pouch venules, blood flow velocity was temporarily altered during and after gentle compression with a fine glass fibre; this was associated with proportional changes in mean cell velocities.4. In four different venules of a hamster cheek pouch, the mean velocity of rolling granulocytes increased in proportion to the mean blood flow velocity (r = 0.963).5. In thirty-six venules of ten mouse mesenteries, the velocities were proportional (r = 0x915) between blood velocities of about 300 and 1000 #um/sec. Above this the velocity of the cells did not increase further.6. The rolling of granulocytes is presumably governed by two forces, the shear force of the flowing blood and an adhesive force between the surfaces of granulocytes and vascular endothelium. Our results suggest that, within limits, the proportionality between the velocities of blood flow and rolling cells is due to shear force, the adhesive force being similar for all the cells. The results suggest that this adhesion force per granulocyte is of the order of 10-5 dynes.

Summary. The retinal microcirculation of anaesthetised normal cats was studied during hyperglycaemia (15 to 55 mmol/1) induced by intravenous infusion of glucose, using high speed cine fluorescence angiography. Saline (0.150 mmol/1) 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 + i 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 ~tl/min to 12 + 1 ~d/min).Key words: Diabetic retinopathy, glucose, vessel calibre, fluorescence angiography, autoregulation, cats.Although there is indirect evidence in man of a correlation between the severity of diabetic retinopathy and the degree of metabolic disturbance [1], there is little indication as to which, if any, of the biochemical disturbances might be responsible. An elevated and fluctuating blood glucose is common to all diabetic syndromes and raises the possibility that hyperglycaemia itself may have an effect on retinal vascular function. In the present study we have thus investigated the effect of acute short-term hyperglycaemia induced by intravenous infusion on retinal perfusion in the normal cat, using high speed cine fluorescence angiography to measure arteriolar inflow and vessel calibre [2]. This technique allows repeated estimations of blood flow during the course of an experiment with an accuracy adequate to register confidence limits varying between approximately 5-15% of the mean [2]. Materials and MethodsThe techniques of cat selection and preparation were as previously described in detail by Hill and Young [2] with some modifications. Healthy domestic cats of either sex weighing between 2.5 and 5.0 kg were anaesthetised with intravenous sodium pentobarbitone (30 mg/kg) following an intramuscular injection of chlorpromazine (2 mg/kg) given 45 min previously as a premedication. Anaesthesia was maintained by continuous IV infusion of sodium pentobarbitone, 9 mg/kg/h. After trachteostomy, respiration of mixed gases (70% N2, 30% OJ was maintained with a Palmer 'Ideal' pump operating at 37 strokes/min with a stroke volume of 9 mi/kg body weight. Blood pressure was monitored continuously using a blood pressure transducer connected to a cannula in one femoral artery and thence to a multichannel recorder. Rectal temperature was similarly monitored continuously using a rectal thermocouple. Blood gases were analysed every 15 minutes from a 0.5 ml arterial blood sample using a Technicon blood gas analyser. Deviations of th...