The lungs have beta 2 receptors and typically bronchodilate when adrenoreceptors are activated. However, when beta blocker drugs are used, bronchoconstriction occurs.
Beta 2 adrenoceptor activation leads to bronchodilation. This is easily remembered by the fact that beta-2 receptors affect two lungs. By blocking beta 2 adrenoreceptor activity, beta blocking medications prevent this dilation and thus indirectly lead to bronchoconstriction in patients. As such, these medications should be used with caution in patients with asthma or COPD.
Adrenergic receptors influence the metabolic system; Beta 3 receptors lead to increased lipolysis, while Beta 2 activation leads to increased insulin release. Thus, beta blocking drugs work to decrease lipolysis and insulin release. In diabetic patients taking insulin, beta blockers block the usual symptoms of hypoglycemia and patients should be aware of their blood glucose.
By blocking beta 2 adrenergic receptors, beta blocking medications decrease insulin release from the pancreas.
Beta blockers block glycolysis (via decreased glucagon release) and decrease lipolysis. Furthermore, glycogenolysis is also decreased.
The ciliary epithelium contains beta adrenergic receptors and ligand binding (epinephrine and norepinephrine) stimulates the formation of aqueous humor. Thus beta blockers decrease aqueous humor formation.
Beta blockers such as timolol and betaxolol decrease aqueous humor formation by blocking beta adrenergic receptors on the ciliary bodies.
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