Figure 4

Plasma concentration-time profile of d -phenyglycine- l -dopa (a), (b) and l -dopa (c), (d) after i.v. (a), (c) and oral (b), (d) administration in Wistar rats (n = 6). The aqueous solution of test compound with dose equivalent to 5.97 mg/kg body weight of l-dopa was administered either intravenously from the tail vein or orally by a feeding tube. Blood samples were collected from the carotid artery at time intervals of from 1 to 180 min. Heparin sodium (25 I.U./ml in 0.3 ml of saline) was added to blood samples, and were then centrifuged at 6,600 g for 5 min. Plasma was stored at -78°C until being analyzed. A 200 μl of the plasma sample in a 10 ml test tube was mixed with 500 μl of 1.0 M Tris buffer (pH 8.6, adjusted by EDTA-2Na⁺) and 10 μl of 3,4-dihydroxybenzylamine (DHBA, 2 μg/ml) was added as internal standard. Alumina 100 mg was then added and then shake for 15 sec and the supernatant was decanted. The alumina was washed four times with 5 ml of water, and the adsorbed compounds on the alumina was eluted with 200 μl of an acidic solution (0.9 ml of glacial acetic acid in 4.0 ml of 1.0 M phosphate buffer). A 30 μl of the eluent was then analyzed by HPLC.