Characterization of L-arginine and aminoguanidine uptake into isolated rat choroid plexus: Differences in uptake mechanisms and inhibition by nitric oxide synthase inhibitors

Recent reports suggest that nitric oxide (NO) may contribute to several neurodegenerative diseases, e.g., focal cerebral ischemia, N-methyl-D- aspartate-mediated neurotoxicity, and experimental autoimmune encephalomyelitis. Accordingly, an understanding of the CNS transport processes of NO synthase (NOS) inhibitors has important therapeutic implications. The objective of the present study was to characterize the in vitro transport processes governing the uptake of L-[¹⁴C]arginine and the NOS inhibitor [¹⁴C]aminoguanidine in rat choroid plexus tissue. Consistent with previous reports, the up take of L-[¹⁴C]arginine was mediated by both saturable and nonsaturable processes and was inhibited by the NOS inhibitors N(G)-methyl-L-arginine, N(G)-amino-L-arginine, and N⁵-imidoethyl-L- ornithine. L-[¹⁴C]Arginine uptake was not inhibited by aminoguanidine or N(G)-nitro-L-arginine. Because aminoguanidine is an organic cation that bears some structural similarity to L-arginine, amino-guanidine might be transported by either an organic cation transporter or by the basic amino acid transporter governing arginine uptake. However, there was no evidence of a saturable uptake process for [¹⁴C]aminoguanidine in isolated rat choroid plexus, in contrast to that observed for L-[¹⁴C]arginine.