Catecholamines: physiological immunomodulators during health and illness.

The existence of an immune-endocrine interaction has been reported and the modulatory effects of the natural occurring catecholamines epinephrine, norepinephrine and dopamine as well as of pharmaceutically generated catecholamines like dopexamine on a wide variety of immune functions were demonstrated. Furthermore, it was noticed that these effects are mediated by specific adrenergic and dopaminergic receptors expressed on the surface of immunological target cells. At first, the adrenergic immunomodulation was predominantly investigated in healthy volunteers and profound immunomodulatory effects were reported for endogenously released and exogenously administered catecholamines. To further elucidate the physiological significance of these interactions, investigators tried to reveal the importance of the catecholaminergic modulation of the immune system under pathological conditions like hemorrhagic shock and systemic inflammation, since catecholamines and adrenergic antagonists are frequently used drugs in the treatment of the critically ill. Furthermore, the interaction between catecholamines and the immune system is supposed to be an important factor in the development of autoimmune diseases and may influence their progress. In addition to the effects of peripheral circulating catecholamines, it was demonstrated that catecholamines that are released within the central nervous system may profoundly influence the activity of the peripheral immune system. Starting with a short historical overview over the immunomodulatory effects of blood catecholamines under good health conditions during critical illness and during autoimmune disease will be reviewed and the immunomodulatory effects of centrally released catecholamines will be discussed.