A physician is conducting a clinical trial for a new hemodynamic drug developed for a variety of indications. The drug's pharmacodynamic profile indicates that it is a pure adrenergic agonist with no significant antagonistic properties. It is infused into a volunteer, and hemodynamic parameters are recorded in the graphs below. Administration of the drug to healthy individuals would most likely result in which of the following physiologic changes?

Question

A physician is conducting a clinical trial for a new hemodynamic drug developed for a variety of indications.  The drug's pharmacodynamic profile indicates that it is a pure adrenergic agonist with no significant antagonistic properties.  It is infused into a volunteer, and hemodynamic parameters are recorded in the graphs below.  Administration of the drug to healthy individuals would most likely result in which of the following physiologic changes?

Quizplus · Accepted Answer

11ec160b_3b9d_ef04_9249_57ed5cb22604_MD0001_00 Administration of the drug caused an increase in systolic and diastolic blood pressures and a reflexive (delayed) decrease in heart rate; these are the typical effects of a selective α₁-adrenergic agonist (eg, phenylephrine, methoxamine). Activation of α₁-adrenoreceptors (in blood vessels of skin and viscera) leads to vasoconstriction and increased systemic blood pressure. Stimulation of baroreceptors in the carotid sinus and aortic arch causes a reflexive increase in vagal influence on the heart. The increased vagal tone results in inhibition of pacemaker activity of the sinoatrial node, slowed conduction through the atrioventricular node, and decreased myocardial contractility. (Choice B) The vasoconstriction caused by α₁-adrenergic agonists increases blood pressure and cardiac afterload, requiring increased myocardial effort to expel the blood. (Choices C and D) Pulmonary capillary wedge pressure reflects left atrial pressure. It is increased after administration of α₁-adrenergic agonists due to increases in cardiac afterload (elevates left ventricular end-diastolic pressure) and venous tone (results in augmented venous return). (Choice E) α₁-adrenergic agonists cause vasoconstriction of the renal and splanchnic arteries, decreasing perfusion to the kidneys and other viscera. Educational objective: α-adrenergic agonists increase systolic and diastolic blood pressure by stimulating α₁-adrenoreceptors in the vascular walls, causing vasoconstriction. The elevated systemic blood pressure then causes a reflexive increase in vagal tone, resulting in decreased heart rate and slowed atrioventricular node conduction. __________ References: Sympathetic neural mechanisms in human cardiovascular health and disease. (http://www.ncbi.nlm.nih.gov/pubmed/19720780) Neural control of the circulation. (http://www.ncbi.nlm.nih.gov/pubmed/21385998) WB4101- and CEC-sensitive positive inotropic actions of phenylephrine in rat cardiac muscle. (http://www.ncbi.nlm.nih.gov/pubmed/7912902)

A Physician Is Conducting a Clinical Trial for a New