Exercise and endorphins--male responses.

The discovery of the endogenous opiates in the mid-1970's has led to a tremendous scientific effort attempting to determine the physiological role of these peptides. An increase in the peripheral plasma levels of beta-endorphin in humans after exercise has been noted by all investigators to date. This indication that the endogenous opiate system is activated during exercise should stimulate investigators to use exercise and training as models to aid in the understanding of these peptides. Unlike most other endocrines, plasma levels of beta-endorphin do not increase proportionally to work intensity. This conclusion is based on only one study and requires corroboration. All human studies to date have used radioimmunoassays, with one exception, and interestingly that study showed no consistent change in plasma levels of leucine enkephalin-like radioreceptor assayable ligands. In males, essentially no information is available concerning the effects of training on either acute or chronic responses to exercise. Studies using opiate antagonists (receptor type-specific) in human and animal models should prove useful in establishing or disproving roles for these peptides in appetite, pain perception, temperature regulation, metabolism, ventilation, and blood pressure control during exercise.