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One of the limiting steps in the regulation of nitric oxide (NO) synthesis is the availability of its precursor, l-arginine, which depends on the presence of a specific uptake system. A characterization of the l-arginine uptake mechanism in the golden hamster retina was performed. This mechanism was stereospecific, saturable, and monophasic, with an apparent K[sub m] of 56.1 ± 2.0 µm and a maximum velocity of 36.0 ± 2.8 pmol/mg prot/min. The basic amino acids l-lysine and l-ornithine but not d-arginine or the nitric oxide synthase inhibitors, N[sup ω]-nitro-l-arginine methyl ester and N[sup ω]-nitro-l-arginine impaired l-arginine influx. Preincubation with l-lysine for 1 h prior to the transport assay significantly stimulated l-arginine uptake. Saturation studies of l-arginine uptake performed at 12.00 and 24.00 h indicated a higher value of V[sub max] at midnight than at midday. When the hamsters were placed under constant darkness or constant light for 48 h and killed at equivalent time points, representing subjective day and subjective night, the differences in l-arginine influx disappeared. Semiquantitative RT-PCR analysis showed that the levels of mRNAs for both CAT-1 and CAT-2B were significantly higher at midnight than at midday. l-Arginine significantly increased cGMP accumulation in a time-dependent manner, with maximal effects during the night. Based on these results, it might be presumed that hamster retinal l-arginine uptake is regulated by the photic stimulus. [ABSTRACT FROM AUTHOR]