<prompt> Powerful vasoconstrictor is-AmphetaminesEpinephrineIsopreenalineDobutamine  <response>: Ans. is b i.e., Epinephrineo Among the given options, only epinephrine has significant action on a-receptor, thus causes vasoconstriction.Sympathomimetic drugsNon selectiveo Adrenaline - a1 a2 b1 b2o Noradrenaline - a1 a2 b1 Slight b1 no. b2o Isoprenaline -b1 b2 b3 but no a actiono Mephentramine - a and bSelectivea1 agonists -Phenylephrine, methoxamine, naphazoline, oxymetazoline, xylometazoline.a2 agonists -Clonidine, methyldopa, brimonidine, apraclonidine, guanfacine, guanabenzb1 agonists -Prenaltemol, dobutamineb2 agonsits -Salbutamol, terbutaline, salmeterol, orciprenaline, ritodrine, isotharine, bitolterol, pirbuterol, tenoterol, formoterol. 