A medical student is observing a pharmacology experiment where drug A is being intravenously administered to a pregnant dog. Some parameters that are being recorded during the experiment include heart rate, blood pressure, pupil size, and uterine contractions. The following diagrams illustrate the measured parameters and observed changes after infusing drug A. Which of the following best characterizes drug A?

Question

A medical student is observing a pharmacology experiment where drug A is being intravenously administered to a pregnant dog.  Some parameters that are being recorded during the experiment include heart rate, blood pressure, pupil size, and uterine contractions.  The following diagrams illustrate the measured parameters and observed changes after infusing drug A.  Which of the following best characterizes drug A?

Quizplus · Accepted Answer

Although the most pronounced effects of adrenergic agonists are those on the heart and vasculature, these drugs also affect many other organs. The graph above illustrates the effects of adrenergic stimulation on the eye and uterus. The pupillary dilator muscle of the eye possesses α1 receptors, and the stimulation of these α1 receptors results in contraction of the pupillary dilator muscle with subsequent dilation of the pupil (mydriasis). Ophthalmic preparation of phenylephrine (selective α-adrenergic agonist) is used to dilate the pupil before ophthalmoscopic examination. Adrenergic receptors of the uterus belong to the β2 group whose stimulation leads to uterine relaxation (an effect called tocolysis) which is used in obstetrics to defer premature labor. Adrenergic β2 agonists such as ritodrine and terbutaline are used for this purpose. The drug in question, therefore, displays both α and β-adrenergic effects. See the table for the summary of end-organ effects of adrenergic agonists. 11ec160b_3c1d_cd43_9249_afff3ee9ce58_MD0001_00 (Choice A) Beta-adrenergic agonists stimulate β2-adrenergic receptors of the uterus and diminish uterine contractions. They do not, however, affect α1-receptors of the eye and would not produce mydriasis. (Choice C) Alpha-adrenergic agonists would produce mydriasis (α1 effect), but not uterine relaxation (β2 effect). (Choice D) Beta-adrenergic antagonists block β2 receptors of the uterus and enhance uterine contraction. They do not affect α1-adrenoreceptors of the pupillary dilator of the eye. (Choice E) Alpha-adrenergic antagonist and beta-adrenergic agonist would cause miosis (pupillary constriction) and uterine relaxation. Educational Objective: Inhibition of uterine contractions (tocolysis) is a result of β2 adrenergic receptor stimulation. Alpha -1 receptor stimulation causes contraction of the ocular pupillary dilator muscle, resulting in mydriasis (pupillary dilation).

A Medical Student Is Observing a Pharmacology Experiment Where Drug