Studies on the metabolism of guanidine compounds in mammals

¹⁴C]Guanidine was observed in the urine after subcutaneous administration to rats of l-guanidino-¹⁴C]arginine or l-guanidino-¹⁴C]canavanine. ${}^{14}\text{C}$]Hydroxyguanidine was additionally detected in the urine after injection of dl-guanidino-¹⁴C]canavanine. These ${}^{14}\text{C}$ metabolites were characterized by high-voltage electrophoresis and paper chromatography, by enzymatic conversion of ¹⁴C]hydroxyguanidine to ¹⁴C]guanidine, and by repeated recrystallization of isolated urinary ${}^{14}\text{C}$]guanidine as the picrate salt with no significant loss of specific activity. These experiments demonstrate that both l-arginine and l-canavanine can serve as precursors of guanidine in the rat.