α2-Adrenoceptor subtypes-mediated physiological, pharmacological actions

α2-Adrenoceptors are involved in various physiological functions, particularly in the cardiovascular system and the central nervous system. Different adrenoceptor subtypes (α2A, α2B and α2C) have been recognised and the different subtypes may have role in activation of distinct physiological and pharmacological pathways. Some of the actions of α2-adrenoceptor stimulants are likely to be mediated exclusively by α2A-adrenoceptor subtype, like antihypertensive and bradycardic effects. α2A-Adrenoceptor may have dominant role in sedative and hypothermic actions, in inhibition of gastric acid secretion and gastric motor activity, as well as in stabilisation of thrombus. Besides α2A-adrenergic receptors α2B and α2C-adrenoceptor subtypes may also be involved in some of the classical effects of α2-adrenoceptor stimulants, like in presynaptic regulation of transmitter release and antinociceptive action. α2B-Adrenoceptor has dominant role in the vasoconstrictor effect of α2-adrenoceptor agonists, and its activation induces contraction of rat uterus in late pregnancy. α2B-Adrenoceptor mediates gastric mucosal protective action initiated centrally in the rat, as well as it may have role also in developmental or reproductive processes. α2C-Adrenoceptor subtypes may be involved in stress-dependent depression and other psychiatric illnesses like attention deficit hyperactivity disorder—together with α2A-adrenoceptor. α2C-Adrenergic receptors seem to mediate peripheral actions as well, like venous vasoconstriction. Identification of separate physiological roles for different α2-adrenergic receptor subtypes could improve design of novel compounds for specific therapeutic goals.