ABSTRACT
A comparative study of the bases, nucleotides and nucleotide-sugars was performed in liver of Bufo arenarum. Samples were obtained at different seasons of the year, according to the periods of active (December-March) and passive metabolism (April-July). It was found that guanine and hypoxanthine increase significantly in spring. A remarkable decrease in the levels of the nucleosides triphosphates adenosine 5'-triphosphate (ATP) and guanosine 5'-triphosphate (GTP) was found in spring; correlatively, an increase in the levels of adenosine 5'-monophosphate (AMP) and guanosine 5'-monophosphate (GMP) and adenosine 5'-pyrophosphate (ADP) and guanosine 5'-pyrophosphate (GDP was observed. A notable increase in the amounts of uridine 5'-diphosphate- D - glucose (UDP-glucose) was detected at the end of the period of low metabolism, which is coincident wtih a decrease in the level of glycogen, observed by other authors.