USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What are some direct effects of alpha-1 agonists on the body?

1. Decreased heart rate

2. Decreased blood pressure

3. Mydriasis

4. Increased lipolysis

The correct answer is: Mydriasis

Alpha-1 agonists primarily activate alpha-1 adrenergic receptors, which are G-protein coupled receptors that mediate various physiological responses. One of the notable effects of alpha-1 agonists is mydriasis, or pupil dilation. Activation of alpha-1 receptors in the radial muscle of the iris causes contraction of this muscle, leading to dilation of the pupil. This mechanism is particularly relevant in pharmacological settings, such as certain eye drops used in ophthalmology. While alpha-1 agonists can lead to other systemic effects like vasoconstriction, which typically increases blood pressure, mydriasis is a direct and observable effect mediated specifically at the eye level. Understanding this action is crucial for recognizing the implications of alpha-1 agonists in clinical practice, particularly in settings involving ocular procedures or conditions requiring pupil dilation.