抄録
The excretion and tissue distribution of radioactivity were comparatively investigated between D- and L-isomers of 3, 4-dihydroxyphenylalanine (DOPA)-2-14C after intravenous and oral administration to rats. Both D- and L-DOPA was eliminated mainly through the urinary route and the initial rate after intravenous administration was faster in the D- than the L-isomer. After oral administration (60 mg/kg), most of radioactivity (85%) from L-DOPA was recovered in the urine, while approximately 50 and 23% from D-DOPA in the urine and feces, respectively, indicating a low absorbability of D-DOPA from the gastrointestinal tract in contrast to an almost complete absorption of L-DOPA. After intravenous administration, the tissue uptake of L-DOPA was significantly higher in most of tissues such as the brain, skeletal muscle, liver, intestine and adrenal. In the pancreas, both isomer showed a high accumulation. After oral administration, the tissue uptake of L-DOPA was significantly decreased and higher than the D-isomer only in the intestine, liver and adrenal, while in all of other tissues including the brain, skeletal muscle and pancreas the n-isomer showed a higher accumulation and a longer retention. This was considered to be due to a considerable metabolism of L-DOPA to dopamine at the peripheral sites as the gastric and intestinal mucosa and liver, while to a gradual absorption and accumulation in the tissues of D-DOPA without being metabolized.
