Centrally acting sympathetic inhibitors for therapy of patients with hypertension

The blood pressure is maintained by the tonic vasomotor activity of efferent sympathetic neurons which are tonically regulated by the rostral ventrolateral medulla (RVLM) in the brain. The alpha 2-adrenoceptor agonist such as clonidine, guanabenz and guanfacine, acts on RVLM to decrease sympathetic neuron activity and lower blood pressure. Drug such as alpha-methyldopa, through its metabolite alpha-methylnoradrenaline, acts like clonidine as an alpha 2-adrenoceptor agonist in the brain. Clonidine and allied drugs except for alpha-methyldopa also bind to imidazoline receptors, which is believed to mediate the hypotensive action. The centrally acting antihypertensive drugs are used for treatment of moderate to severe forms of hypertension and are effective in patients with renal failure. The treatment with these drugs induces central nervous system side effect of sedation and drowsiness, which limits the clinical usefulness and are believed to be mediated by central alpha 2-adrenoceptors. The new imidazoline compounds, rilmenidine and moxonidine, which selectively act on imidazoline receptors, may be a useful antihypertensive drug without such central side effects.