Biogenic amines

Question 1

Melanin characteristics

Answer 1

Synthesis involves: Tyrosine to DOPA by tyrosine hydroxylase, and DOPA to dopaquinone by tyrosinase

Eumelanin = eye, skin and dark hair
Pheomelanin = yellow to red hair

Question 2

How are eumelanin and pheomelanin formed?

Answer 2

Eu: Alpha MSH binds to MC1R

Pheo: Agouti protein to MC1R

Question 3

What is the rate limiting step of catecholamine synthesis?

Answer 3

Formation of DOPA from tyrosine, catalyzed by tyrosine hydroxylase

Underproduction of dopamine = Parkinson’s

Question 4

Catecholamine synthesis basics

Answer 4

Tyrosine to DOPA via tyrosine hydroxylase. DOPA to Dopamine. Dopamine to Norepinephrine. Norepi to Epinephine via PMNT

Question 5

Catecholamine function?

Answer 5

Dopamine and Norepi increase heart rate and vasoconstriction

Question 6

Characteristics of pheochromocytoma

Answer 6

Excessive secretion of epi and norepi (adrenal tumor)

Palpitations, headache, perspiration

Hyperglycemia is seen, due to excess glycogenolysis

Question 7

Monoamine oxidase inhibitors

Answer 7

MAO degrades neurotransmitters

MAO inhibitors (MAOIs) allows NTs to escape degradation, thus allowing NTs to accumulate and bind to their receptors (antidepressants)

Question 8

What enzyme inactivates dopamine, epi and norepi?

Answer 8

COMT

Question 9

Serotonin characteristics

Answer 9

Tryptophan -> 5-hydroxytrytophan -> serotonin

Selective serotonin reuptake inhibitors (SSRIs) increase levels of serotonin (antidepressants)

Both a decrease of blood serotonin and an increase of serotonin reuptake leads to increased depression

Question 10

Nitric oxide characteristics

Answer 10

Arginine, using NADPH -> Citrulline + NO

ACh released in the blood activates NO synthase, causing the above reaction

NO diffuses into smooth muscle cells, eventually relaxing them

Question 11

Histamine characteristics

Answer 11

Secreted by mast cells as a result of trauma and allergy

Cimetidine interferes with the synthesis / action of histamine