Central alpha 2 receptors and the regulation of blood pressure in humans.

Alpha 2 receptors in the brain stem and in the periphery inhibit sympathetic activity and thus lower blood pressure. Alpha 2 receptor agonists such as clonidine or guanabenz reduce central and peripheral sympathetic overflow and via peripheral presynaptic receptors may reduce peripheral neurotransmitter release. Alpha 2 agonists lower blood pressure in many patients either alone or in combination with diuretics. Central nervous side effects are less common when lower doses are used. More recent analogues of clonidine with greater alpha 2 receptor selectivity have been found to have a longer duration of action and may be less likely to lead to a withdrawal reaction, with rebound of hypertension and symptoms, when treatment is interrupted.