Alpha-1 receptors are a type of adrenergic receptor found in various tissues throughout the body. They primarily respond to the neurotransmitters norepinephrine and epinephrine, which are involved in the body's fight-or-flight response. When activated, alpha-1 receptors cause smooth muscle contraction, leading to effects such as increased blood pressure and pupil dilation. These receptors play a crucial role in regulating vascular tone and are important in conditions like hypertension and nasal congestion. Medications that target alpha-1 receptors can help manage these conditions by either blocking or stimulating their activity, influencing blood flow and other physiological responses.