Part 6 Flashcards
Functions of histamine
*gastric acid secretion
*acts as a neurotransmitter
* chemotaxis of white blood cells
Functions of histamine and which receptor is bound
Gastric acid secretion-H2
Vasodilation- H1
Contraction of smooth muscles except in blood vessels -H1
Increased vascular permeability-H1
Cardiac stimulation- H2
Effects of histamine
Reddening, wealing, flaring
Pathological effects of histamine
Gastric acid secretion (H2)- treated with H2receptor antagonists
*Ligand for type 1 hypersensitivity eg urticaria, hay fever (H1)- treated with H1 receptor antagonists
H3 receptors
Mainly for neurotransmission and consists of autoreceptors and heteroreceptors
* A presynaptic autoreceptor
* a gprotein coupled receptor
H4 receptors
Mainly for immunomodulation (immunity)
Eg immune cell chemotaxis, immune response
H1 receptors
Allergic inflammation eg urticaria, rhinitis
H1 receptor antagonists or inverse agonist
Chrorpheniramine , cetirizine, diphenhydramine
H2 receptor antagonist
Cimetidine , ranitidine
Reduce gastric acid secretion and treat ulcers
Where are H1 receptors found
Smooth muscle , endothelium, brain
Where are H2 receptors found
Gastric mucosa, cardiac cells , mast cells, brain
What prevents motion sickness
First generation H1 antagonist (muscarinic effect)
First generation antagonists
Eg chlorpheniramine
Binds to histamine receptors, a adrenergic receptor, muscarinic nicotinic receptors and serotonin receptors
These antagonist Cross the blood brain barrier and thus they cause sedation
Side effects 1st generation H1 antagonists
Sedation
Second generation H1 receptor antagonists
Eg cetirizine, fexofenadine
These do not cross the blood brain barrier so they don’t have side effects like sedation, sleepiness, cognitive impairment
*Most of these are witter ionic compounds
Do histamine receptors have constitutive activity
Yes H2 antagonists are inverse agonists
Pitolisant
Inverse agonist of H3 histamine autoreceptors used for treatment of narcolepsy
Where are H3 receptors located
Presynaptic autoreceptors and heteroreceptors, brain ,myenteric plexu, other neurons
Where are H4 receptors located
Eosinophils, neutrophils , CD4 T cells
Where are H4 receptors used
Chronic inflammatory conditions like asthma
Endogenous adrenergic receptor agonists
Noradrenaline
Dopamine
Adrenaline
Exogenous adrenergic receptor agonists
Isoprenaline
B1 adrenoceptor
Found in the heart and increases heart rate
B2 adrenoceptor
Smooth muscle relaxation
Uses of B- adrenoceptor antagonists
Treat: hypertension
Irregular heart rhythms
Heart failure
Heart attack
Migraine
Propranolol
Non selective b adrenoceptor antagonist that causes bronchoconstriction and is life threatening in asthmatic patients
