ABSTRACT
This chapter provides some of the issues concerning the experimental approach to the assessment of the pharmacodynamic effects of beta agonists, concentrating particularly on assessment of selectivity. Selectivity of beta agonists is defined in terms of relativity to the effects of isoprenaline, a nonselective agonist at beta receptors. It has stimulatory activity at both receptor types for any dose. An agonist selective at the beta2 receptor would stimulate that receptor with little or no effect at the beta1 receptor. Much of the original work investigating the pharmacological effects of beta agonists were performed before ligand-binding studies to beta1 and beta2 receptors were established; thus, definitions of selectivity may have been inaccurate. In vitro studies were receptor directed in that they used tracheal relaxation as an indicator of beta2 receptor activation, whereas increase in heart rate and contractility were thought to represent beta1 receptor stimulation.
