alpha(2)-Adrenoceptor subtypes-mediated physiological, pharmacological actions

Abstract

alpha(2)-Adrenoceptors are involved in various physiological functions, particularly in the cardiovascular system and the central nervous system. Different adrenoceptor subtypes (alpha(2A), alpha(2B) and alpha(2C)) have been recognised and the different subtypes may have role in activation of distinct physiological and pharmacological pathways. Some of the actions of alpha(2)-adrenoceptor stimulants are likely to be mediated exclusively by alpha(2A)-adrenoceptor subtype, like antihypertensive and bradycardic effects. alpha(2A)-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 alpha(2A)-adrenergic receptors alpha(2B) and alpha(2C)-adrenoceptor subtypes may also be involved in some of the classical effects of alpha(2)-adrenoceptor stimulants, like in presynaptic regulation of transmitter release and antinociceptive action. alpha(2B)-Adrenoceptor has dominant role in the vasoconstrictor effect of alpha(2)-adrenoceptor agonists, and its activation induces contraction of rat uterus in late pregnancy. alpha(2B)-Adrenoceptor mediates gastric mucosal protective action initiated centrally in the rat, as well as it may have role also in developmental or reproductive processes. alpha(2C)-Adrenoceptor subtypes may be involved in stress-dependent depression and other psychiatric illnesses like attention deficit hyperactivity disorder-together with alpha(2A)-adrenoceptor. alpha(2C)-Adrenergic receptors seem to mediate peripheral actions as well, like venous vasoconstriction. Identification of separate physiological roles for different alpha(2)-adrenergic receptor subtypes could improve design of novel compounds for specific therapeutic goals.