A medical student is conducting a pharmacology experiment to determine the effects of a certain drug. She infuses this drug intravenously over different dose ranges and measures several important hemodynamic parameters. Graphs plotting the observed changes in renal blood flow and cardiac output are shown below. Which of the following drugs was most likely used in this experiment?

Question

A medical student is conducting a pharmacology experiment to determine the effects of a certain drug.  She infuses this drug intravenously over different dose ranges and measures several important hemodynamic parameters.  Graphs plotting the observed changes in renal blood flow and cardiac output are shown below.  Which of the following drugs was most likely used in this experiment?

Quizplus · Accepted Answer

11ec160b_3b9f_0078_9249_034720c96a43_MD0001_00 Dopamine is an adrenergic agonist that has varying effects based on the dose. At low doses, dopamine stimulates D1 receptors in the renal vasculature and tubules, inducing an increase in renal blood flow, glomerular filtration rate, and sodium excretion. Vasodilation of the mesenteric, cerebral, and coronary vascular beds is also prominent at low doses. As the dosage increases, dopamine begins to stimulate β₁adrenergic receptors in the heart, increasing cardiac contractility, heart rate, and systolic blood pressure. At the high end of the dose range, stimulation of α₁receptors in the systemic vasculature leads to generalized vasoconstriction, which can result in decreased cardiac output due to the increased afterload. (Choice B) Edrophonium is a short-acting acetylcholinesterase inhibitor used in the diagnosis of myasthenia gravis (ie, Tensilon test). Through its cholinergic effects, edrophonium reduces heart rate, cardiac conduction, and cardiac contractility. (Choice C) Epinephrine increases heart rate, myocardial contractility, and cardiac output by stimulating β₁ receptors. At low doses, stimulation of β₂ receptors in the skeletal muscle vasculature produces vasodilation that can cause decreased blood pressure. At high doses, α₁-induced vasoconstriction in the skin and viscera becomes more pronounced. Epinephrine does not significantly increase renal blood flow (even at lower doses) due to the lack of D₁ receptor stimulation. (Choice D) Esmolol is a cardioselective β₁ blocker with a short duration of action. Esmolol decreases heart rate, myocardial contractility, and cardiac conduction without affecting renal blood flow. (Choice E) Phenylephrine is a selective α₁-adrenergic receptor agonist that causes a generalized increase in peripheral vascular resistance and blood pressure. Its use results in significant renal, splanchnic, and mesenteric vasoconstriction. Educational objective: Low-dose dopamine infusion stimulates D₁ receptors in the renal and mesenteric vasculature, resulting in vasodilation and increased blood flow to these sites. Increasing doses of dopamine stimulate β₁ and α₁ receptors, resulting in increased cardiac output and elevated systemic vascular resistance. At the high end of the dose range, the increase in afterload can result in decreased cardiac output.

A Medical Student Is Conducting a Pharmacology Experiment to Determine