Alpha-1 receptors are a type of adrenergic receptor that respond primarily to the neurotransmitters norepinephrine and epinephrine. They are found in various tissues throughout the body, including blood vessels, the heart, and the eyes. When activated, these receptors typically cause smooth muscle contraction, leading to effects such as increased blood pressure and pupil dilation. These receptors play a crucial role in the body's response to stress and are involved in the sympathetic nervous system activities. Medications that target alpha-1 receptors can be used to treat conditions like hypertension and nasal congestion by either blocking or stimulating these receptors.