Ans. is 'b' i.e., Methyl Dopa Centrally Aeting Svmpatholvticso These drugs reduce sympathetic outflow from vesopressor centers in brainstem. Examples are :1 .Clonidine3.Guanabenz5. Rilmenidine2. Methyldopa4. Guanfacine6. MoxonidineClonidineo It acts (partial agonist) on a, receptors, especially a2A in brainstem - Stimulation of receptors in medulla (vasomotor centre) - decrease sympathetic outflow - fall in BP and bradycardia (also due to enhanced vagal tone).o a2A receptor stimulation is responsible for sedation produced by clonidine.o Clonidine also binds to a nonadrenergic receptor, imidazoline receptor, which may also mediate antihypertensive effect.o Rilmenidine and moxonidine are selective cerebral imidazoline receptor agonists with little or, action - equivalent antihypertensive action with low sedative property.o Rapid r'.v. injection of clonidine raises BP transiently due. to activation of peripheral postsynaptic vasoconstrictor a2B receptors at high concentrations so attained. Ora! doses producing lower plasma levels cause only fall in BP, because clonidine has lower intrinsic activity on a2B receptors which predominate in vascular smooth muscle,o Uses of clonidine# Hypertension# Opioid withdrawl# Menopausal syndrome# Alcohal withdrawal# Smoking cessation# Loose motions in diabetic neuropathy# Test for pheochromocytoma o Abrupt discontinuation of clonidine therapy can lead to rebound hypertension (treated with phentolamine); therefore this drug is not suitable for people having travelling job like business executives who are likely to miss the doses.Methvldopao It is a prodrug - a-methyl norepinephrine formed in the brain from methyldopa acts on a-receptor in brainstem- decrease sympathetic out flow.o In large doses, methyldopa inhibits the enzyme dopa decarboxylase in brain and periphery - reduces NA synthesis and forms the false transmitter methyl-NA in periphery as well,o Methyldopa is DOCfor hypertension in pregnancy.Guanabenz and guanfacin are centrally active antihypertensive drugs that share the central otj-adrenoceptor- stimulating effects of clonidine.