title: Citrulline uptake in rat cerebral cortex slices: modulation by Thioacetamide -Induced hepatic failure.
abstract: L-citrulline (Cit) is a co-product of NO synthesis and a direct L-arginine (Arg) precursor for de novo NO synthesis. Acute liver failure (ALF) is associated with increased nitric oxide (NO) and cyclic GMP (cGMP) synthesis in the brain, indirectly implicating a role for active transport of Cit. In the present study we characterized [(3)H]Cit uptake to the cortical brain slices obtained from control rats and rats with thioacetamide (TAA)-induced ALF ("TAA slices"). In both control and TAA slices the uptake was partially Na(+)-dependent and markedly inhibited by substrates of systems L and N, including L-glutamine (Gln), which accumulates in excess in brain during ALF. Cit uptake was not affected by Arg, the y(+)/y(+)L transport system substrate, nor by amino acids taken up by systems A, xc (-)or XAG. The Vmax of the uptake in TAA slices was ~60 % higher than in control slices. Chromatographic (HPLC) analysis revealed a ~30 % increase of Cit concentration in the cerebral cortical homogenates of TAA rats. The activity of argininosuccinate synthase (ASS) and argininosuccinate lyase (ASL), the two enzymes of Cit-NO cycle catalyzing synthesis of Arg, showed an increase in TAA rats, consistent with increased ASS and ASL protein expression, by ~30 and ~20 %, respectively. The increased Cit-NO cycle activity was paralleled by increased expression of mRNA coding for inducible nitric oxide synthase (iNOS). Taken together, the results suggest a role for Cit in the activation of cerebral NO synthesis during ALF.
authors.affiliation: Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, Pawinskiego 5, 02-106, Warsaw, Poland, mzielinska@imdik.pan.pl.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Zielińska
authors.forename: Marta
authors.initials: M
authors.lastname: Obara-Michlewska
authors.forename: Wojciech
authors.initials: W
authors.lastname: Hilgier
authors.forename: Jan
authors.initials: J
authors.lastname: Albrecht
mesh_terms: D000818:Animals; D001120:Arginine / Q000378:metabolism; D001123:Argininosuccinate Lyase / Q000378:metabolism; D001124:Argininosuccinate Synthase / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D002956:Citrulline / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D017093:Liver Failure / Q000139:chemically induced* / Q000378:metabolism; D008297:Male; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009569:Nitric Oxide / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013853:Thioacetamide / Q000633:toxicity*
chemical_list: D009419:Nerve Tissue Proteins; D013853:Thioacetamide; D002956:Citrulline; D009569:Nitric Oxide; D001120:Arginine; D001123:Argininosuccinate Lyase; D001124:Argininosuccinate Synthase