Which one of the following is not an alphaadrenoceptor agonist ?

Ans. is 'b' i.e. Methyldopa All the given drugs are a-adrenaceptor agonist o Amongst the given option, methyldopa is best answer (read text below) o Methyldopa, itself is not an alpha adrenoreceptor agonist; its a prodrug. It is metabolized in adrenergic neurons first to a-methyldopamine and then to a-methylnorepinephrine, which then acts on a receptors as agonists. o The other three drugs mentioned are a,-adrenergic agonists, act on a2Asubtype. o All these drugs i.e. Clonidine, Guanabenz, Guanafacine and the a-methyl norepinephrine (formed from a-methyl dopa) act on central a2 receptors, resulting in a reduction in sympathetic outflow from CNS. Thus cause a decrease in blood-pressure.