Abstract
The primary objectives of this study were to classify subjects into responder types, to validate this typology through the use of pharmacological blockade and multiple laboratory tasks, and to explore the relationship between reactor type and adrenergic sensitivity. Subjects were 25 black and 30 white healthy men, aged 18-25. Subjects participated in three reactivity sessions scheduled one week apart. The speech, cold pressor, and mirror tracing tasks were completed during each session. Tasks were preceded by oral drug administration (the beta-blocker metoprolol, the alpha-blocker prazosin, or placebo). Additionally, each subject was infused with a corresponding agonist to index adrenergic sensitivity. Blood pressure, heart rate, and impedance-derived parameters were measured.Using regression-derived cut scores, subjects were classified into myocardial, vascular, and mild reactor types based on cardiac output and total peripheral resistance changes elicited by the preparation period of the speech task. Analyses revealed that, under placebo conditions, myocardial subjects responded to the speech preparation task with increased myocardial activity, to the speech presentation task with increased myocardial and vascular activity, and to the cold pressor with increased vascular activity. Myocardial subjects were unresponsive to the mirror tracer task. Both vascular and mild subjects responded across tasks with increased vascular activity.Analyses of pharmacological data show that myocardial subjects show decreased reactivity in myocardial parameters in response to a beta-adrenergically mediated task under conditions of beta-blockade. Conversely, vascular subjects demonstrate decreased reactivity in vascular parameters in response to an alpha-adrenergically mediated task under alpha-blockade. Additionally, under placebo conditions, myocardial subjects exhibited increased beta-adrenergic activity, while vascular subjects exhibited increased vascular activity relative to other groups. Reactor groups did not differ in terms of adrenergic sensitivity. These results lend credence to the notion that the reactor type classification employed in this study constitutes a valid typology.