1. Bioassay of histamine using guinea-pig ileum
Lab # 8

2. Outline Description of ileum Histamine receptors
Dose-response curve of histamine

3. Ileum
3/5 of intestine
Empties in the large intestine via ileocecal valve
Bile salts, vitamin B12, water and electrolytes absorption
Doesn’t have myogenic contraction
More sensitive to histamine action

4. Histamine receptors H1 H2 H3 H4 R subtype Distribution Action Agonist
Antagonist H1
Sm. muscle
Contraction
Hist.
Mepyramine
Cyproheptadine H2
Gastric mucosa
Acid release
Cimetidine
Ranitidine H3
Presynaptic
Autoregulation of histamine release
Thioperamide H4
Eosinophils
Neutrophils
CD4T cells
Modulate the production of blood cells & cytokines

5. Histamine receptors in ileum
H1 receptors
Receptor type: G-protein-coupled receptor
Agonist: Histamine
MOA: ++ G-protein → ++phspholipase C → splitting of PIP2 into 1) DAG that increases the opening of calcium channels 2)IP3 which increases calcium mobilization from sarcoplasmic stores;
DAG & IP3 lead to increase in the intracellular concentration of calcium and smooth muscles contraction.

6. Bioassay of histamine using three-point assay
W+N
W+N
W N
W+N
0.05 St.
0.1 St.
0.2 St
0.1 T
0.9 St.
0.12 St
0.2 St
0.3 St.
0.4 St.
0.1 T
0.1 St.

7. Curves
On semi-log paper
On normal paper *
Ht.
Ht. * *
Log Dose
Dose

8. Conc. = 10 mcg/ml
S1= 0.1 ml ~ 0.1 mcg
S2 = 0.12 ml ~ 0.12 mcg
T = ( ) /2 = 1.1 mcg