Biphasic actions of L-DOPA on the release of endogenous dopamine via presynaptic receptors in rat striatal slices.

In rat striatal slices, 30 nM of L-DOPA increased the impulse (5 Hz)-evoked release of dopamine (DA), without increasing the spontaneous release and tissue content of DA. The minimum dose required to increase spontaneous DA release was 0.1 microM and the dose which led to an accumulation of DA was 100 microM. In the presence of NSD-1055, a DOPA-decarboxylase inhibitor, L-DOPA-induced increases in spontaneous DA release were prevented and L-DOPA produced dual actions on the evoked release of DA, a stereoselective propranolol-sensitive increase at 30 nM and a stereoselective sulpiride-sensitive decrease at 1 microM. L-DOPA produces dual presynaptic regulatory actions on DA release, via facilitatory beta-adrenoceptors at 30 nM and inhibitory DA receptors at 1 microM. The primary action of L-DOPA appears to be the facilitation of release of DA rather than the conversion to DA.