There are two main types of adrenergic receptors: the î± and î²- adrenoceptors. noradrenaline shows slight selectivity for the î± receptor, whereas isoprenaline shows selectivity for the î² adrenoceptor. adrenaline shows no selectivity and binds equally well to both the î± and î²-forms of the adrenoceptors. draw the chemical structures for noradrenaline, isoprenaline, and adrenaline. suggest an explanation for these differences in selectivity relative to the binding site of each receptor.