Developmental Changes of Catecholamine-mediating Enzyme - Dopamine-β- Hydroxylase and Its Cofactors in Central and Peripheral Tissues and Serum of Long-Evans Rats

Dopoamine-β-hydroxylase (DBH) is a catecholamine-synthesizing enzyme which catalyzes the formation of norepinephrine from dopamine. Fifty nine Long-Evans rats of 1 week-old were used to grow on normal diets in 7 different developmental stages, viz., 15 rats in 1 week-old group, 9 rats in 2 weeks-old group, and the remaining 35 rats were divided equally into five groups, 7 rats in each group of 5-, 8-, 12-, 15- and 27-weeks old for systematic developmental studies of DBH. At the end of each developmental period, weights of rats were recorded for that specific group and they were sacrificed. The brain tissues (caudate nucleus, hypothalamus, brain stem, colliculi, cerebral cortex and cerebellum) and peripheral tissues (liver, heart, kidney, adrenal, spleen, pancreas, lung and small intestine) and serum were collected. The brain tissues had the highest activity (expressed as nmole/min/g of wet weight tissue) of DBH at 5 weeks of age. The hypothalamus had the highest activities (11.5 ± 2.2) and the lowest activities were found in the cerebellum (5.7 ± 0.9). The peripheral tissues also showed the peak DBH activities at 5 weeks of age and adrenals had the highest activities (59.2 ± 7.0) among the central and peripheral tissues. The serum DBH activities were relatively low (1.3 ± 0.2) as compared to those in all other tissues. The highest serum DBH activities (1.28 ± 21 nmole/min/ml of serum) were also found in the 5- weeks-old rats. The specific activities of DBH were also measured in various developmental stages and the results were found to be in agreement with the DBH activities expressed in terms of gram of tissues or milliliter of serum. The Km and Vmax values for DBH were measured in the serum samples of each group and the highest Vmax values (78.3 ± 21.2 pmol/min/mg protein) were obtained at 5 weeks of age; while the lowest Km values (0.52 ± 0.04 mM) were obtained at this stage of age.