Characterization and Tissue Localization of Catecholamine Synthesizing Enzymes
Authors: M. Goldstein, K. Fuxe, T. Hökfelt
Journal: Pharmacological Reviews (1972)

1 . Three enzymes involved in catecholamine biosynthesis, namely, aromatic-L-amino acid decarboxylase (AADC), dopamine-β-3-hydroxylase (DβH) and phenylethanolamine-N-methyl transferase (PNMT) were purified from bovine adrenal glands. The purified enzymes were used to induce the production of the corresponding immullologically pure antienzymes in rabbits. The latter were utilized for immunochemical studies as well as for localization of catecholamine synthesizing enzymes in peripheral tissue and brain by the indirect immunofluorescent method.

2. Immunochemical studies reveal heterogeneity of DβH and PNMT among different species. Bovine PNMT occurs in different molecular forms and differently charged isozymes were separated from the low molecular form of the enzyme. The PNMT charged isozymes are indistinguishable from each other on immunoelectrophoresis. The corticoid inducible PNMT is immunologically distinguishable from the uninducible form.

3. AADC was localized in all medullary cells and in all catecholamine and serotonin containing cell bodies of the peripheral and central nervous system. DβH was localized in adrenal medullary cells, peripheral and central norepinephrine cell bodies and transected peripheral and central norepinephrine nerve fibers. The primitive catecholamine cell system in the ganglia lacks specific DβH immunofluorescence and seems therefore to contain dopamine and not norepinephrine. PNMT was localized in the cytoplasm of most of the adrenal medulla glands in rats and mice and in all medullary cells in the guinea pig. By combining the immunofluorescence technique with the formaldehyde condensation technique it was possible to separate the norepinephrine containing cells from the epinephrine containing cells in the adrenal medulla of rats.

4. Serum DβH activity was assayed by a sensitive enzymatic procedure. The activity of this enzyme in serum depends on the rate of release of the enzyme from the sympathetic innervated tissues and on the rate of degradation in some sites not yet known. Evidence was presented that serum DβH levels are altered by changes in the sympathetic nervous system functions.

Human serum DβH activity increases with age; infants under 1 year of age have extremely low enzyme activity levels. The enzyme activity was investigated in patients with various disorders. Extremely high values were found in some neuroblastoma patients and low values in some patients with familial dysautonomia. The latter finding implies the involvement of the parasympathetic system in the regulation of serum DβH levels.

5. The effects of hypophysectomy on catecholamine synthesizing enzymes was investigated. The increase in the turnover rate of cardiac norepinephrine after hypophysectomy is associated with an increase in circulatory DβH. Chronic treatment with ACTH restores the turnover rate of cardiac norepinephrine and the serum DβH levels to almost normal levels. PNMT activity as well as the PNMT-protein content is markedly reduced in the adrenals of hypophysectomized animals and histochemical studies reveal a marked reduction in number and/or size of medullary cells. Thus, atrophic changes in adrenal medulla may contribute to the decrease in the levels of catecholamine synthesizing enzymes after hypophysectomy.