Structure of the Sympathetic Nervous System

Within the varicosities, norepinephrine is stored in small membrane-enclosed vesicles (granules, 0.05 to 0.2 pm in diameter). In the axoplasm, L-tyrosine is Lullmann, Color Atlas of Pharmacology ( [Pg.82]

The effect of released norepinephrine wanes quickly, because approx. 90% is actively transported back into the axoplasm, then into storage vesicles (neuronal re-uptake). Small portions of norepinephrine are inactivated by the enzyme catechol-0-methyltransferase (COMT, present in the cytoplasm of postjunctional cells, to yield normeta-nephrine), and monoamine oxidase (MAO, present in mitochondria of nerve cells and postjunctional cells, to yield 3,4-dihydroxymandelic acid). [Pg.82]

The liver is richly endowed with COMT and MAO it therefore contributes significantly to the degradation of circulating norepinephrine and epinephrine. The end product of the combined actions of MAO and COMT is van-illylmandelic acid. [Pg.82]

All rights reserved. Usage subject to terms and conditions of license. [Pg.82]

Second neuron of sympathetic system, varicosity, norepinephrine release [Pg.83]

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