The effect of simultaneous administration of 3,4-dihydroxyphenylpyruvic acid and L-dopa on the bioavailability of L-dopa in rat and mouse.

In the rat, administration of 3-(3,4-dihydroxy)-L-phenylalanine (L-dopa) simultaneously with the corresponding alpha-keto acid, 3,4-dihydroxyphenylpyruvic acid (DHPPA), gives significantly higher concentrations of L-dopa in the serum and of dopamine and homovanillic acid in the brain than the same dose of L-dopa alone. Correspondingly, DHPPA potentiates the effect of L-dopa on the locomotor activity in reserpine-treated mice. DHPPA is postulated to increase the absorption of intact L-dopa from the gut by preventing the transamination reaction between L-dopa and the physiological alpha-keto acids.