The regulation of striatal tyrosine hydroxylase. Effects of gamma hydroxybutric acid and healperidol.

Gamma-hydroxybutyric acid (GHBA) in doses that increased the striatal dopamine (DA) content of rat brain failed to increase the affinity of striatal tyrosine hydroxylase (TH) for its pterdine cofactor or to change the sensitivity of the enzyme to the inhibition by DA. Haloperidol (1 mg/kg) decreased the apparent Km of striatal TH for the pteridine cofactor. However, when GHBA was injected before haloperidol it prevented the decrease in the apparent Kn of TH, in a dose related manner. In vitro GHBA (10(-4) M) neither changed the stimulation of the striatal adenylyl cyclase by DA nor its inhibition by haloperidol. These results suggest that in striatal dopaminergic terminals the Kn of TH for the pteridine cofactor is regulated by an molecuular mechanism which requires that the impulse flow in the DA neurons is unimpaired.