Adrenocortical Responses of Humans to Group Hierarchy, Confinement and Social Interaction

Abstract

The response of the adrenal gland is the most widely used index of the presence of a stress response. Plasma corticosteroids show a well defined diurnal rhythm, with the peak occurring in the early morning hours in man and other diurnal animals whereas nocturnal rodents show their peak in the evening, at lights-off. In addition, the responsiveness of the adreno-cortical system to stimuli also varies diurnally. Sampling time therefore, becomes of fundamental importance in studies using plasma corticosteroids as an index of stress or other psychophysiological relationships. It should also be noted that the majority of the existing literature on the subject is derived from data obtained by testing and sampling in the morning hours, which coincides with the peak of the rhythm in man and diurnal primates, and the trough of the rhythm in rats, mice and nocturnal primates. Experimental conditions that may disturb this rhythm only compound the problem of reliable data interpretation.