Physical exercise, endogenous opioids and immune function.

The experimental data available today strongly indicate that various types of physiological stressors, including physical exercise and emotional stress, can influence immune function. Natural immunity represents a first line of defence in viral infections and cytotoxicity to a variety of tumour cells. Natural immunity is strongly influenced by chronic exercise and this regulation includes interaction between the nervous, endocrine and immune systems. Central mechanisms including the endogenous opioids are of great interest. Chronic activation of endogenous opioid systems augments natural cytotoxicity and the possible involvement the opioids in the exercise-induced enhancement of natural immunity is discussed. Also, catecholamines seem to play an important role in the regulation of immune function, both after chronic exercise and emotional stress. The physiological significance of the reported changes in natural cytotoxicity after exercise-training is as yet unclear.