histamines and anti-histamines

Question 1

physiology

Answer 1

most of bodily histamine is stored in mast cells –> GI tract, lungs, skin
- acts on g protein coupled receptors - H1, H2, H3, H4
- circadian clock gene regulates histamine transport

Question 2

What is the effect of each receptor?

Answer 2

H1 - smooth muscle –> relaxation and vasodialation to improve vascular permeability + promotes wakefulness and arousal
H2 - GA secretion, increase CO and HR
H3 - CNS - decrease memory storage, decrease histamine release
H4 ?

*if we want to promote wakefulness, antihistamine must act on H3 - histamine in CNS keeps people awake

Question 3

triple response of histamine

Answer 3

1. reddening
2. localised oedma
3. wheeling

Question 4

what type of agonist are H1 receptor blocking agonists? Why?

Answer 4

inverse agonists - shuts of cell response rather than preventing due to constitutive activity

Question 5

sedating antihistamines

Answer 5

• can cross BBB
• inhibit H1 receptor
• promethazine
• doxylamine used in short-term treatment of insomnia
• last 8-30 hrs

Question 6

non-sedating anti-histamines

Answer 6

• limited crossing of BBB
  do not block muscarinic receptors
  treat allergy
  longer half-lives - taken daily or twice a day