Nitric oxide synthase activity and L-arginine metabolism in the retinas from streptozotocin-induced diabetic rats.

1. Nitric oxide synthase (NOS) activity was studied in the retinas from normal rats and in the retinas from two groups of streptozotocin-induced (8 days and 4 months) diabetic rats. In each animal group, the NOS activity was correlated to the concentration of amino acids related to L-arginine metabolism and to L-arginine uptake. 2. Retinas from both groups of streptozotocin-induced diabetes (8 days and 4 months) showed an increased NOS activity compared with the NOS activity in retinas from normal rats. In retinas lysate from normal rats, the NOS activity was most potently inhibited by NO-Arg (1 mM), whereas, in both groups of streptozotocin-induced diabetes, the NOS activity was most potently inhibited by the NOS inhibitor aminoguanidine (0.5 mM). 3. The basal levels of the amino acids related to L-arginine metabolism-namely, L-arginine, L-citrulline, L-ornithine and L-glutamine-in retinas from both groups of rats with streptozotocin-induced diabetes were decreased compared with the amino acid levels in retinas from normal rats. 4. The uptake of L-[3H]arginine in retinas from both groups of rats with streptozotocin-induced diabetes was increased compared with the uptake of of L-[3H]arginine in retinas from normal rats.