The transport kinetics across the plasma-aqueous and plasma-vitreous barriers were studied in normal and long-term
streptozotocin-diabetic rats, using trace amounts of [14C]-
L-glucose and [3H]-
3-O-methyl-D-glucose. The former is passively transported while the latter uses the same transport-facilitating system as
D-glucose. Transport rates of
L-glucose were significantly higher in the diabetic rats, with ocular entry rates from the plasma being increased by 69% across both barriers. Thus, the data indicate that in experimental diabetes the passive permeability of the blood-ocular barriers is significantly increased. By contrast, calculated transport rate constants for
3-O-methyl-D-glucose, when adjusted for the
hyperglycemia and the increased passive
glucose movement, are not altered in the diabetic animal. Nevertheless, there is actually more mass
D-glucose movement due to the prevailing
hyperglycemia. The present study suggests that although
streptozotocin diabetes alters plasma-ocular
glucose transport, there is no direct impairment of
glucose carrier function. Alterations in transport occurred at both ocular barriers, suggesting that involvement is general and that both the retinal pigment epithelium and the ciliary epithelium may be affected by the diabetes. It is unknown whether the increase in passive movement is related to the prevailing
hyperglycemia or to
insulin deficiency or other unknown factors.