Metabolic fate of 3,4-dihydroxyphenylpyruvic acid(DHPP) in rats. II. In vivo evaluation of DHPP as a possible new precursor of brain dopamine.

Abstract

Metabolic fate of 3,4-dihydroxyphenylpyruvic acid-2-14C (DHPP-2-14C) in rats was investigated and a rapid conversion of DHPP to L-3,4-dihydroxyphenylalanine (L-dopa) was demonstrated in vivo. After i.v. administration, a high uptake of the radioactivity was observed in the adrenal medulla, caudate nucleus, pancreas, hair follicle and renal medulla, in a similar way as L-dopa-2-14C. DHPP itself appeared not to pass through the blood-brain barrier. After oral administration, very little uptake of the radioactivity was observed in the brain even at high doses (10, 50 and 100 mg/kg.) Most radioactivity was recovered into the urine (about 44.0% and 85.4% after oral and i.v. administration, respectively) but respiratory excretion of the radioactivity was also observed (28.01 and 6.30% after oral and i.v. administration, respectively). In order to evaluate the efficacy of DHPP as oral precursor of brain dopamine, the brain and other tissue uptake of the radioactivity were compared between DHPP-2-14C and L-dopa-3-14C after oral administration at various dosages. The results revealed only extremely low uptake of radioactivity in the brain after DHPP administration as compared to L-dopa. This was found to be mainly due to an extremely slower absorption of DHPP than L-dopa from intestine.