L-DOPA POTENTIATES PRESYNAPTIC INHIBITORY ALPHA-2-ADRENOCEPTOR-MEDIATED 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. UK]4304 (0.1 - 1 muM), a selective alpha2-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 alpha2-adrenoceptors but not those of angiotensin II receptors on rat hypothalamic NA neurons.