Binding to postsynaptic alpha1-adrenergic receptors of the vascular wall, they (phenylephrine, etc.) cause contraction of smooth muscle, vasoconstriction and increased blood pressure (see HYPERTENSION). This group includes clonidine, guanfacine, methyldopa, etc. Penetrating through the BBB, they stimulate presynaptic ALPHA2-adrenergic vasomotor center of the brain, reduce the secretion of neurotransmitter in the synaptic cleft and reduces the flow sympathetic impulses from the Central nervous system, which leads to a decrease in blood pressure. Another effect of alpha1-agonists (indanazoline, Xylometazoline, naphazoline, etc.) is the decrease in the secretion in the nasal cavity and the relief of nasal respiration (see DECONGESTANT).