Glucose transport across ocular barriers in vivo in the rat was previously studies in this laboratory. General kinetic equations were developed describing transport into ocular humors after a bolus injection of labeled substance in blood. Using rate parameters it was demonstrated that the transport of D-glucose from blood to aqueous and vitreous humors is consistant with a carrier-mediated model of facilitated diffusion. Our preliminary studies with the long term streptozotocin (SZ) - diabetic rats have revealed decreased plasma-aqueous and plasma-vitreous transport constant for 3-0-methyl-D-glucose (3-OMG) which can be attributed to carrier saturation on the basis of infusion experiments in normal animals. Thus, little if any, impairment of blood-ocular D-glucose carrier function is observed in the diabetic animal, the high absolute glucose entry rates due to the hyperglycemia. In addition, we have demonstrated a significant increase in passive L-glucose transport across the plasma aqueous and plasma vitreous barriers indicating a loss of barrier integrity and suggesting an epithelial defect due to the hyperglycemia or insulin deficiency. The proposed studies of passive and carrier mediated glucose transport across eye epithelial in normal and SZ-diabetic rats and guinea pigs are designed to determine the role of insulin deficiency and hyperglycemia in the diabetic. Specifically we propose: (1) to study, in vivo, the time of onset and development of changes in carrier-mediated 3-OMG and passive L-glucose transport into aqueous and vitreous humors, lens and cornea as a function of the level and duration of the diabetes using kinetic methods developed by us; (b) to determine insulin transport effects as distinct from hyperglycemic effects in vivo using a growth hormone diabetic model and SZ model which allow transport measurements at a full range of insulin levels; (c) to study insulin, hyperglycemia and osmotic effects across isolated retinal pigment epithelium and ciliary epithelium of the frog and guinea pig in vitro using short circuited Ussing type chambers; (d) to study in vitro rates of transport of 3-OMG and L-glucose in cell suspension preparations to pigment epithelium and ciliary epithelium of normal and diabetic rats and guinea pigs: (e) to study the specific binding of 125I insulin in cell preparations of the various eye epithelia that may be found to be insulin sensitive.
