Free amino acids and the uptake and binding of taurine in the central nervous system of rats treated with guanidinoethanesulphonate.

The content of free amino acids in the central nervous system, the uptake of taurine by slices and synaptosomes and taurine binding to synaptic membranes have been studied on adult male Wistar rats after a prolonged administration of 2-guanidinoethanesulphonate with or without a taurine-free diet. The 2-guanidinoethanesulphonate administration both alone and together with a taurine-free diet considerably reduced taurine levels in all regions studied, viz. cerebrum, cerebellum, brain stem and spinal cord, but the contents of methionine and gamma-aminobutyric acid were increased. On the normal diet the maximal taurine loss occurred after a 3-week 2-guanidinoethanesulphonate administration, when also the 2-guanidinoethanesulphonate accumulation in the cerebrum was largest. On the taurine-free diet the taurine levels were still low after the 4-week 2-guanidinoethanesulphonate administration when the taurine content in cerebral synaptosomes was also reduced to almost one half. 2-Guanidinoethanesulphonate treatment modified the uptake and binding processes of taurine in the synaptosomal preparations. The maximal high-affinity taurine uptake was reduced, whereas the affinity of the specific sodium-independent binding sites for taurine increased. The results suggest that the neuromodulator properties of taurine could be affected by the reduced taurine levels and/or by the accumulated 2-guanidinoethanesulphonate.