Different types of centrally acting antihypertensives and their targets in the central nervous system

The central regulation of blood pressure and other cardiovascular parameters may involve the baroreceptor reflex arc, including both adrenergic and serotonergic pathways, as well as amino acids, as neurotransmitters. Both adrenergic and serotonergic pathways have been recognized as targets for clinically relevant, centrally acting antihypertensives, such as clonidine, guanfacine, and α-methyl-DOPA. The central components of the hybrid drugs urapidil and ketanserin also involve serotonergic pathways and receptors. For urapidil the stimulation of 5-HT_1A-receptors is assumed to induce peripheral sympathoinhibition, whereas for ketanserin the central mechanism is unknown in detail. More recently central imidazoline (I₁) receptors have been proposed as the major target for the newer antihypertensives rilmenidine and moxonidine. Clonidine, however, is assumed to be mixed I₁- and alpha₂-receptor agonist. The distinction between central I₁- and alpha₂-receptors may potentially offer the design of new antihypertensives, acting like clonidine but with fewer side effects. Finally, the amino acid pathways should be considered as potential targets for centrally acting antihypertensives. Experimental compounds on this basis are available but clinical implications appear to be very remote. In the present survey an outline is given of the various pathways, neurotransmitters, and receptors involved in the central regulation of blood pressure. The different types of centrally acting antihypertensives are subsequently discussed on this basis.