L-TYROSINE AND NICOTINE INDUCE SYNTHESIS OF L-DOPA AND NOREPINEPHRINEIN HUMAN-LYMPHOCYTES

Catecholamines (CA) were studied in peripheral human lymphocytes in ba sal conditions as well as after L-tyrosine and/or acetylcholine (ACh) stimulation. Nicotinic and muscarinic receptor activation and blockade were assessed. CA were determined after ultrasonic cell disruption in peripheral lymphocytes after incubation (1 h at 37 degrees C) with th e chemicals employed. L-tyrosine significantly increased (P < 0.01) L- Dopa and norepinephrine (NE) content of lymphocytes. ACh in the low mu M range did not modify, whereas ACh (60 mu M) and (120 mu M) signific antly increased (P < 0.01), both L-Dopa and NE intracellular levels. L -tyrosine plus ACh (60 mu M) or (120 mu M) significantly increased(P < 0.01) intracellular L-Dopa and NE versus control, versus L-tyrosine a lone and versus ACh alone. The increase was higher than the algebraic sum of the individual increases; Nicotine (250 mu M), but not muscarin e (50 mu M), significantly increased L-Dopa and NE in lymphocytes. Tet raethylammonium (500 mu M) (nicotinic blocker), but not atropine (100 mu M) (muscarinic blocker), inhibited the ACh-mediated increase of int racellular L-Dopa and NE. These data show that lymphocyte synthesis of CA is under nicotinic control. Since intracellular L-Dopa after L-tyr osine plus ACh increased 6-fold versus basal, 2-fold versus L-tyrosine alone and 3-fold versus ACh alone, it is concluded that ACh might reg ulate CA synthesis in lymphocytes through an activation of the rate li miting enzyme tyrosine hydroxylase.