ICI 118 551 hydrochloride (CAS No 72795-01-8) is a selective beta-2 adrenergic receptor antagonist used primarily in biomedical research to investigate cardiovascular and respiratory functions Originating from studies on adrenergic signaling pathways it inhibits the cyclic AMP pathway by blocking beta-2 adrenergic receptors which are involved in smooth muscle relaxation and bronchodilation Its activity in vitro is often observed in the nanomolar to low micromolar range ICI 118 551 hydrochloride is frequently utilized in cell models and animal studies to explore its effects on heart rate vascular resistance and airway responsiveness It is also a valuable tool in drug screening assays aiming to identify compounds that interact with adrenergic receptors Experimental concentrations typically depend on the specific research design allowing versatility in its application across various experimental settings