Beschreibung:
. After intraperitoneal administration of l‐2−14C‐3‐O‐methyldopa (14C‐O‐methyldopa) to rats, the amino‐acid was distributed evenly in blood, brain, heart, adipose tissue and liver, whereas it accumulated more in the kidney and the pancreas. 14C‐O‐methyldopa showed a biological half‐life of about 12–13 h in blood, brain and heart.. The concentration curve of 14C‐O‐methyldopa in brain (after increasing doses of the amino‐acid) was linear if measured 2 h after administration, but seemed to reach a plateau at the higher doses if determined after 16 h.. The concentrations of 14C‐O‐methyldopa metabolites (mainly homovanillic acid and 4‐hydroxy‐3‐methoxyphenyllactic acid) were low, except in the kidney, and varied according to the tissue.. Twenty‐four hours after administration of 14C‐O‐methyldopa, 33% of the injected radioactivity appeared in the urine. This radioactivity consisted of about 95% of metabolites (probably in the main 14C‐homovanillic acid and 14C‐4‐hydroxy‐3‐methoxyphenyllactic acid) and of 5% of unchanged 14C‐O‐methyldopa. In the faeces, 10% of the radioactivity appeared, mainly as metabolic end‐products.. It is concluded that 14C‐O‐methyldopa easily penetrates from the blood into various tissues, including brain, and that the majority of the amino‐acid undergoes a slow metabolism. The different shape of the concentration curves for 14C‐O‐methyldopa in the brain after 2 and 16 h might indicate the presence of two tissue pools of the amino‐acid.