Studies on the precursor of methylguanidine in rats with renal failure.

Each of creatinine (Cr), guanidinoacetic acid (GAA) and arginine (Arg) was administered intraperitoneally to rats with renal failure, and the levels of methylguanidine (MG) in the serum, liver, kidney, muscle and urine were determined at certain intervals. The levels of MG in the serum, liver, kidney, muscle and urine after Cr administration increased markedly with time. The amount of total MG at 24 h was estimated to be 114 micrograms/100 g body weight, which accounted for 0.46% of the Cr dose. In contrast, changes in MG levels after administration of GAA or Arg were only slight in comparison with those after Cr administration. Thus, MG was proved to be produced mainly from Cr.