Absorption, distribution and excretion of DL-gamma-amino-beta-hydroxybutyric acid-1-14C (GABOB-1-14C) in the rat.

1. Serum levels of DL-gamma-amino-beta-hydroxybutyric acid-1-14C (DL-GABOB-1-14C) in the rat (50 mg/kg) were quite similar after single i.v. and p.o. doses. Also the disappearance from the serum was similar with both administration routes. Within 6 days after p.o. treatment with the same single dose, about 26.5% and 1.6% of the dose were excreted in the urine and the faeces, respectively, and after i.v. administration excretion was 10.15% in urine and 1.75% in faeces. The results show that the compound is well absorbed and retained by the organism. After repeated oral doses (200 mg/kg three times daily for 4 days) the serum levels tended to become constant. 2. Urinary excretion after repeated administration increased progressively every day. Investigations on bile-cannulated rats showed that about 0.4% of the p.o. dose was excreted in 24 h. 3. After single (50 mg/kg) or multiple p.o. doses (200 mg/kg) of GABOB-1-14C, there was no unusual localisation of radioactivity in the organs the highest concentrations being present in the liver and the kidneys. Brain radioactivity was not related to serum levels or to administration route. Radioactivity concentration in other organs, for example the liver, was a function of serum levels. 4. Investigations performed to identify the radioactive products in the brain showed that the radioactivity was mainly ascribable to the unchanged DL-GABOB-1-14C.