Physiological control of brain norepinephrine synthesis by brain tyrosine concentration

The intraperitoneal administration of tyrosine to rats causes proportional increases in brain tyrosine levels and in the accumulation of the norepinephrine metabolite 3-methoxy-4-hydroxy-phenylethyleneglycol-sulfate (MOPEG-SO₄) after probenecid. Brain tyrosine level after tyrosine administration or after the consumption of a single meal is also positively correlated with brain MOPEG-SO₄ accumulation in rats that do not receive probenecid but are subjected to cold stress. These observations extend our earlier finding that brain tyrosine level can affect the rates at which catecholaminergic neurons synthesize and turn over their transmitters.