Adrenergic agonist Drugs

Question 1

isoproterenol

Answer 1

• nonselective β adrenergic agonist.
• increases cardiac contractility (positive inotropic effect) by acting on myocardial β-1 adrenergic receptors.
• also binds to β-2 adrenergic receptors and causes vasodilation by relaxation of vascular smooth muscle, leading to decreased vascular resistance and mean arterial blood pressure.
  negligible effects on α-1 adrenergic receptors.
• increases the cardiac rate and output as well as the pulse pressure.

Question 2

Adenosine

Answer 2

• acts on A1 receptors on cardiac cells and activates potassium channels
• increasing potassium conductance
• leads to transient conduction delay through
  the atrioventricular node.
• can also cause peripheral vasodilation, but it attenuates the adrenergic-mediated increase in myocardial contractility.

Question 3

Phenylephrine

Answer 3

• selective alpha-1 adrenergic receptor agonist that causes marked arterial vasoconstriction when administered intravenously.
• increase in systemic vascular resistance and blood pressure.
• induced blood pressure increase elicits a baroreceptor-mediated increase in vagal tone, which results in decreased stroke volume and a slowed heart rate
• pulse pressure, defined as the systolic pressure minus the diastolic pressure, is decreased by phenylephrine because of the reflex decrease in stroke volume and the increased afterload.
• sympathomimetic drug with pure α adrenergic agonist activity.
• causes vasoconstriction with an increase in systemic vascular resistance.

Question 4

Dobutamine

Answer 4

complex adrenergic agonist whose physiologic effects are primarily the result of beta-adrenergic receptor agonism
- increases the heart’s rate and contractility while exerting little effect on peripheral vascular resistance.

Question 5

Epinephrine endogenous catecholamine that stimulates both alpha- and beta-adrenergic receptors

Answer 5

endogenous catecholamine that stimulates both alpha- and beta-adrenergic receptors

• Infused intravenously, epinephrine increases the pulse rate and pulse pressure and decreases the peripheral vascular resistance.
• The latter finding is due to the dominant effect of epinephrine on beta-2 adrenergic receptors compared to its effect on alpha-1 receptors.

Question 6

Norepinephrine

Answer 6

acts on α-1 receptors, causing vasoconstriction and an increase in systemic vascular resistance.
- acts as a weak agonist at β-1 receptors, with a modest increase in myocardial contractility.