Presynaptic: b2 on adrenergic nerve terminals to facilitate the release of norepinephrine
Postsynaptic (in the effector organ): b1 adrenoceptors ,b2 adrenoceptors and b3 adrenergic receptors
Beta 1 Adrenoceptor Stimulation:
- Heart: increase all cardiac properties (contraction, Heart rate
- Kidney: Increase renin release.
- Fat cells: lipolysis
Beta 2 adrenoceptor stimulation:
- Relaxation of smooth muscle fiber of large blood vessels leading to VD of coronary, skeletal, pulmonary, and renal arterioles leading to hypotension
- Relaxation of bronchial muscle.
- Relaxation of uterus,
- Relaxation of Wall of U.B.
- Relaxation of Wall of GIT leading to decrease gut motility.
- Decrease mast cell degranulation.
- Hepatic glycogenolysis. Leading to increase blood glucose
- Increase aqueous humor formation.
- Decrease plasma K.
- Skeletal muscle tremors.
- T4 to T3 conversion
- Presynaptic b2 facilitates NE release.
May lose selectivity, to stimulate beta 1 in high doses resulting in tachycardia and tremors
Beta 3 adrenoceptors stimulation:Y
- Increase lipolysis in fat cells.
All adrenergic receptors are present in the wall of GIT causing relaxation.