L-dopa potentiates presynaptic inhibitory alpha 2-adrenoceptor- but not facilitatory angiotensin II receptor-mediated modulation of noradrenaline release from rat hypothalamic slices.

L-dopa is a potentiator for presynaptic beta-adrenoceptors. We studied whether L-dopa potentiates the activities of other presynaptic receptors to modulate the evoked noradrenaline (NA) release in rat hypothalamic slices. UK14304 (0.1-1 microM), a selective alpha 2-agonist, concentration-dependently inhibited NA release. Noneffective 10 pM L-dopa potentiated the UK14304-induced inhibition. This potentiation was selectively antagonized by 1 nM L-dopa methyl ester, a competitive L-dopa antagonist, while yohimbine antagonized both the inhibition by UK14304 alone and its potentiation by L-dopa. However, 10 pM L-dopa produced no effect on angiotensin II (0.1-1 nM)-induced facilitation. L-dopa potentiates activities of presynaptic beta- and alpha 2-adrenoceptors but not those of angiotensin II receptors on rat hypothalamic NA neurons.