A 66-year-old man comes to the emergency department due to several episodes of lightheadedness and a recent fall. The symptoms are especially pronounced in the morning when he gets up from bed. The patient takes medications for hypertension, stable angina pectoris, gout, and benign prostate hyperplasia. He also has osteoarthritis of the right knee and takes occasional nonsteroidal anti-inflammatory drugs. His blood pressure is 120/80 mm Hg and pulse is 70/min in the supine position, and 90/60 mm Hg and 87/min on standing, respectively. Cardiopulmonary examination is normal. Blockade of which of the following receptors is most likely contributing to this patient's current condition?

Question

A 66-year-old man comes to the emergency department due to several episodes of lightheadedness and a recent fall.  The symptoms are especially pronounced in the morning when he gets up from bed.  The patient takes medications for hypertension, stable angina pectoris, gout, and benign prostate hyperplasia.  He also has osteoarthritis of the right knee and takes occasional nonsteroidal anti-inflammatory drugs.  His blood pressure is 120/80 mm Hg and pulse is 70/min in the supine position, and 90/60 mm Hg and 87/min on standing, respectively.  Cardiopulmonary examination is normal.  Blockade of which of the following receptors is most likely contributing to this patient's current condition?

Quizplus · Accepted Answer

11ec160b_3b98_e5ed_9249_c5a389eeae53_MD0001_00 This patient has orthostatic (postural) hypotension, which is characterized by a drop in blood pressure on standing from the supine position (>20 mm Hg systolic and/or >10 mm Hg diastolic). Standing causes pooling of a significant amount of blood (500-1000 mL) into the veins below the heart. This initiates the following sequence of events in otherwise healthy individuals: The α1-adrenergic antagonists (terazosin, doxazosin) are commonly used for symptomatic benign prostate hyperplasia and are often associated with orthostatic hypotension, resulting in lightheadedness and syncope due to cerebral hypoperfusion upon standing. Other etiologies of orthostatic hypotension include volume depletion (hypovolemia due to hemorrhage, hyperglycemia, or diuretics) and autonomic dysfunction (Parkinson disease, diabetes). (Choice B) Blockade of presynaptic α2-adrenergic receptors results in increased release of norepinephrine from peripheral nerve terminals. This effect results in increased blood pressure and heart rate. (Choice C) The β1-adrenergic receptors are found predominantly in the heart. Their stimulation increases heart rate, contractility, and conduction. Blockade of β1-adrenoreceptors would prevent this patient's heart rate from increasing appropriately upon standing (normally about 10-25/min). (Choice D) Stimulation of β2-adrenergic receptors causes bronchodilation, vasodilation in skeletal muscles, and uterine relaxation. Blockade of β2-adrenoreceptors is associated with peripheral vasoconstriction and bronchoconstriction and would not cause orthostatic hypotension. (Choice E) D1-adrenergic (dopaminergic) receptors are located in the walls of renal, splanchnic, and mesenteric blood vessels. Stimulation of these receptors causes vasodilation and increased renal and splanchnic blood flow. Blockade of D1 receptors does not result in orthostatic hypotension. Educational objective: Orthostatic hypotension is a frequent cause of lightheadedness and syncope and is defined as a decrease in systolic (>20 mm Hg) or diastolic (>10 mm Hg) blood pressure on standing from the supine position. Medications (α1-adrenergic antagonists, diuretics), volume depletion, and autonomic dysfunction are common causes of orthostatic hypotension. __________ References: A review of the etiology, associated comorbidities, and treatment of orthostatic hypotension. (http://www.ncbi.nlm.nih.gov/pubmed/23656967) Alpha1-Adrenoceptor subtype selectivity and lower urinary tract symptoms. (http://www.ncbi.nlm.nih.gov/pubmed/15544022)

A 66-Year-Old Man Comes to the Emergency Department Due to Several