Abstract
I read the recent review article by Hashim 1 with interest. As part of a human physiology research group, we have examined the role of the central serotonergic and dopaminergic systems as mediators of the onset of fatigue during prolonged exercise in environmental extremes. Our research data suggest that prolactin may be a potential biochemical marker of hyperthermia. 2,3 Hyperprolactinaemia is observed during the later stages of exhaustive aerobic exercise and is significantly greater during the later stages of prolonged exercise in the heat than in temperate or cool environments. 2 Our data 3 also suggest that the observed prolactin response is non-linear over time and is related to the extent of increase in core temperature above 38–38.5°C. The physiological function of an increase in the circulating concentration of prolactin during exercise-induced hyperthermia remains unclear. However, prolactin has been implicated in the control of sweat gland function, increasing sweat rate and the production of a more dilute sweat, further suggesting an association with thermal regulation. Our observations are primarily experimental based within controlled laboratory environments. Further clinical studies would be required to define the role of prolactin as a potential marker of hyperthermia.
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