Advanced Dental Admission Test (ADAT)

What is the primary effect of A1 adrenergic receptors?

1. Vasodilation

2. Vasoconstriction

3. Relaxation

4. Increased heart rate

The correct answer is: Vasoconstriction

The primary effect of A1 adrenergic receptors is vasoconstriction. When A1 receptors are activated, they typically cause smooth muscle contraction in blood vessels, leading to their narrowing. This physiological process increases vascular resistance, which can elevate blood pressure and reduce blood flow to certain areas of the body. Vasodilation, relaxation, and increased heart rate are not the primary responses associated with A1 adrenergic receptor activation. Instead, vasodilation typically occurs through the activation of A2 or other adrenergic receptors, which promote the relaxation of vascular smooth muscles. Similarly, relaxation is generally linked with different receptor types, and an increased heart rate is mainly mediated by beta-adrenergic receptors rather than A1 receptors. Thus, the dominant action attributable to A1 adrenergic receptors is indeed vasoconstriction.