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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 speci®c uptake system. A characterization of the L-arginine uptake mechanism in the golden hamster retina was performed. This mechanism was stereospeci®c, saturable, and monophasic, with an apparent K m of 56.1 2.0 lM 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 x -nitro-L-arginine methyl ester and N x -nitro-Larginine impaired L-arginine in¯ux. Preincubation with L-lysine for 1 h prior to the transport assay signi®cantly stimulated L-arginine uptake. Saturation studies of L-arginine uptake performed at 12.00 and 24.00 h indicated a higher value of V 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 in¯ux disappeared. Semiquantitative RT-PCR analysis showed that the levels of mRNAs for both CAT-1 and CAT-2B were signi®-cantly higher at midnight than at midday. L-Arginine signi®-cantly 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.

Background: Rabies virus infection causes encephalitis, which is almost always fatal. Vaccination can be extremely effective at preventing disease but is prohibitively costly. Vaccine formulations allowing dose-sparing and fewer inoculations with faster antibody response would be extremely desirable. IMT504, an immunostimulatory non-CpG oligodeoxynucleotide, is a highly potent vaccine adjuvant. Methods: Human and rat antibody measurements, and rat challenge studies were performed. Results: In rats, highly effective immune responses with IMT504 were observed even after diluting vaccine up to 1/625. In highly lethal, live intracerebral rabies challenge studies, protection occurred even with extremely dilute vaccine plus IMT504. In humans, antibody titers developed faster and were significantly higher with IMT504-adjuvanted diluted vaccine vs non-adjuvanted vaccine (full strength or diluted). All five administered IMT504-adjuvanted diluted vaccine reached protective antibodies (≥0.5 IU/ml) after the second injection. After the third injection, individuals receiving IMT504-adjuvanted diluted vaccine reached levels approximately 10 times higher than controls (M ± SEM: 31.0 ± 10.9 vs 3.40 ± 0.99 IU/ml). Conclusions: These data suggest that IMT504 may allow fewer inoculations, highly significant dose-sparing of vaccine, rapid antibody production and protection from rabies. Extensive clinical studies are necessary to confirm if the use of IMT504 will permit significantly greater access to highly effective life-saving rabies vaccines.

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