"Aromatic amino acid decarboxylase catalyzes the cytosolic conversion of L-DOPA to dopamine, although all naturally occurring aromatic L-amino acids are substrates for the enzyme. The enzyme so rapidly decarboxylates L-DOPA that the levels of the amino acid are relatively low, and supplying the enzyme with additional substrate can lead to increased product formation, which is the basis of L-DOPA treatment for Parkinson’s disease. The accumulation of DOPA following inhibition of aromatic amino acid decarboxylase provides an index of synthesis rate.

Dopamine-β-hydroxylase is located inside amine storage vesicles of norepinephrine neurons. Dopamine is actively transported from the cytoplasm into the vesicles. As the enzyme is a copper containing protein, its activity can be inhibited by copper chelating agents, such as diethyldithiocarbamate and FLA-63. Inhibition of the enzyme effectively reduces tissue norepinephrine levels. The enzyme does not have a high degree of substrate specificity."

basically, rate limiting steps for the synthesis of both. There is also substantial evidence with ADHD research that suggests that the two modulate each other. Due to the pathway in which dopamine can be created, it is more likely that norepinephrine is increased by dopamine levels, not the other way around.

Check out this figure concerning the biosynthesis of norepinepherine from dopamine.

https://www.greatplainslaboratory.com/articles-1/2018/7/23/inhibition-of-dopamine-conversion-to-norepinephrine-by-clostridia-metabolites-appears-to-be-a-the-major-cause-of-autism-schizophrenia-and-other-neuropsychiatric-disorders

Check out this as well if you are so inclined!