Non-Endocrine Aspects of Stress

NON-ENDOCRINE ASPECTS OF STRESS M. S. GOLDSTEIN, M.D., AND E. R. RAMEY, Ph.D.* Environmental constancy is both an object and an artifact of research. In a more natural setting, organisms must continually deal with a world of shifting temperatures; food and water supply; lightand darkness; foraging, fighting, and fleeing; infections, parasites, and saprophytes. The animal is continually adapting his various activities to preserve his structure and function in the face ofthe whims ofa labile environment. Severe changes both in the medium in which the organism exists and in the elicited responses within the animal have been considered under the heading of stress. Most physiological phenomena are adaptive responses. Thus the increased contractility of the heart muscle in response to increased venous return, the growth ofbody hair on exposure to cold, the hypertrophy of skeletal muscle with work, the accelerated catabolism offat stores on fasting , can be described as adaptive processes. The dynamic character of the maintenance ofbodily processes and the turnover ofconstituent materials suggest that any change induced in one area of function would at some point be reflected in virtually every other system ofthe body. Such a generalized view ofadaptive mechanisms quickly embraces all biological information and creates too complex a framework for the study ofspecific systems ofresponse. It is experimental limitation which makes it necessary to restrict observations of the stress response to artificially designated physiological systems. I. The "Common Pathways" ofResponse to Stress At least two major concepts have been proposed in describing the crucial mechanisms which determine the response to stress. Both have * Department of Metabolic and Endocrine Research, Michael Reese Hospital, Chicago, Illinois, and Department ofPhysiology, Georgetown University School ofMedicine, Washington, D.C. 33 been characterized by an emphasis on a specific "common pathway." This is evident in the work of Cannon's group, on the one hand, and Selye's group, on the other. The response ofan organism to a hostile or "threatening" change in internal or external environment was considered by Cannon to be organized around the sympathetic nervous system and the adrenal medulla and by Selye to be organized around the pituitary-adrenal cortical "axis." Both these groups, however, reported observations which could not be included readily in their respective central theses. Such considerations were justifiably minimized at the time, in favor ofthe exciting, more all-embracing working hypothesis. Interest in the adrenal cortex and the general adaptation syndrome has eclipsed Cannon's concepts ofsympathetic activation and ofhomeostasis. There is, however, an increasing body of information which relates the autonomic nervous system to the functions of the adrenal cortex in the stress response. In any event, the "fight or flight" emergency role of the sympathetic nervous system, as proposed by Cannon and his co-workers, did not demand that all the phenomena ofadaptation be included in the schemata of the original hypothesis. While they suggested that the epinephrine -mediated increase inblood clotting might be considered preparation for potential traumatic bleeding, they also recognized that these changes in clotting time were an independent and obligatory result ofincreased sympathetic activity. Responses to stress need not subserve a useful function in the teleological sense. Further, Cannon's formulation does not require that each apparently relevant reaction be a direct function of sympathetico-medullary activation. Much of the data reported by this group cannot in fact be categorized in this fashion. Homeostasis is a convenient description of regulation of certain functions . Those functions which lend themselves to this type ofconsideration are actually removed from direct involvement with intimate tissue needs. It is blood pressure which is "homeostatic" and not the resultant minute flow past a cell where exchange ofmaterials occurs. It is blood sugar which is "homeostatic" and not the uptake and conversion ofglucose to various forms of useful biological energy. Sympathetic activation in response to stress temporarily alters such homeostatic regulation in meeting the changing needs imposed by the suddenly altered environment. However, submitting any such response to detailed investigation ofmechanism quickly leads to involvement of metabolic, renal, cardiac, etc., phenomena. The 34 M. S. Goldstein and E. R. Ramey ¦ Stress Perspectives in Biology and Medicine · Autumn 1957 non-mechanistic description ofhomeostasis is set aside. The sympathetic activation becomes part ofa more...