Autocids Pharmacology

Question 1

What is the precursor of histamine?

Answer 1

Histidine, converted by histidine decarboxylase.

Question 2

What are the main metabolites of histamine?

Answer 2

N-methylhistamine

Imidazole acetic acid (IAA)

N-methylimidazole acetic acid.

Question 3

Which enzymes degrade histamine?

Answer 3

Histamine N-methyltransferase and monoamine oxidase (MAO), or diamine oxidase (DAO).

Question 4

What is a urinary diagnostic marker of histamine overproduction?

Answer 4

N-methylimidazole acetic acid (NMIAA).

Question 5

Where is histamine primarily stored?

Answer 5

In mast cells in skin, bronchial mucosa, and gut mucosa.

Question 6

Where is histamine synthesized de novo and not stored in granules?

Answer 6

Brain, stomach, healing tissues, and some skin cells.

Question 7

What triggers histamine release from mast cells?

Answer 7

Cross-linking of IgE antibodies on mast cells by allergens.

Question 8

Which kinases are activated during IgE-mediated histamine release?

Answer 8

Lyn and Syk (tyrosine kinases).

Question 9

What role does phospholipase C (PLC) play in histamine release?

Answer 9

It produces IP3, leading to Ca²⁺ release and histamine granule exocytosis.

Question 10

Which molecules bind histamine inside granules?

Answer 10

Heparin
chondroitin sulfate
proteases.

Question 11

How does histamine inhibit its own release?

Answer 11

Via H2 receptor-mediated increase in cAMP.

Question 12

What is the role of beta-2 receptors on mast cells?

Answer 12

Also increase cAMP and inhibit histamine release.

Question 13

Name non-IgE (anaphylactoid) triggers of histamine release.

Answer 13

Morphine, succinylcholine, contrast media, dextran, neuropeptides, wasp venom.

Question 14

What causes itching, burning, and warmth in histamine reactions?

Answer 14

Sensory nerve stimulation and vasodilation.

Question 15

What is the triple response to histamine?

Answer 15

Red spot (vasodilation), wheal (leakage), flare (axon reflex).

Question 15

What G protein pathway is associated with H1 receptors?

Answer 15

PLC → IP3 → Ca²⁺ release → smooth muscle contraction.

Question 16

What G protein pathway is associated with H2 receptors?

Answer 16

Adenylate cyclase → cAMP → increased acid secretion.

Question 17

What is unique about H3 receptor signaling?

Answer 17

Mediates Ca²⁺ entry from extracellular space, found mainly in CNS.

Question 18

What CNS functions involve H1 receptors?

Answer 18

Wakefulness, appetite suppression, thermoregulation, ADH secretion.

Question 19

How does histamine affect the heart?

Answer 19

H2 → ↑HR and force;

H1 → ↓AV conduction time; high doses may cause arrhythmias.

Question 20

What are H1 antagonists used for?

Answer 20

Allergies (hay fever, rhinitis), motion sickness, vomiting, urticaria.

Question 21

What are H2 antagonists used for?

Answer 21

Peptic ulcers, GERD, dyspepsia.

Question 22

What are common H2 blockers?

Answer 22

Cimetidine, ranitidine, famotidine, nizatidine.

Question 23

What distinguishes classical vs. new generation H1 antagonists?

Answer 23

New generation are non-sedating, longer-acting, less anticholinergic.

Question 24

Which H1 blockers are associated with risk of PVT?

Answer 24

Astemizole and terfenadine (when combined with CYP450 inhibitors like erythromycin).

Question 25

Histamine levels in the plasma are normally ……..?

Answer 25

very low.

Question 26

Histamine levels in the ….. are high.

Answer 26

CSF

Question 27

Histamine levels in the CSF are …….

Answer 27

high

Question 28

Histamine has a high turnover(made quickly, destroyed quickly) and low steady state level. True or false?

Answer 28

True

Question 29

The IgE receptor has an ……… which belongs to syk family of kinases.

Answer 29

intracellular domain

Question 30

The IgE receptor has an intracellular domain which belongs to ……. family of kinases.

Answer 30

syk

Question 31

Phosphorylation of the …….. activates the tyrosine kinase (Lyn).This activated tyrosine kinase cross phosphorylates the other tyrosine kinase (Syk) on the other ……..?

Answer 31

tyrosine IgE receptors

Question 32

The phosphorylation of the ……… allows phosphorylation of the enzymes phospholipase C.

Answer 32

Syk tyrosine kinase

Question 33

The phosphorylation of the Syk tyrosine kinase allows phosphorylation of the enzymes ………..

Answer 33

phospholipase C.

Question 34

Describe Ca2+ dependent exocytosis?

Answer 34

Ca2+ results in the release of granules (Ca2+ dependent exocytosis). The stored granules have a pH of 5.5. At this PH histamine is positively charged.It is held inside the granule by ionic interaction with negatively charged molecules also in the granule.

Question 35

What is autoinhibition?

Answer 35

The histamine released can act on the mast cell it came from and inhibit the further release of histamine

Question 36

How does histamine carry out auto inhibition?

Answer 36

Histamine does this by acting on a H2 receptor on the mast cell

Question 37

Diseases associated with increased histamine?

Answer 37

• Urticaria pigmentosa(mastocytosis) • Systemic mastocytosis. • Myelogenous leukemia. • Gastrinoma