Exercise thermoregulation and hyperprolactinaemia

The anterior pituitary hormone prolactin (PRL), measured in the peripheral blood circulation, reflects alterations in central brain 5-hydroxytryptamine (serotonin) and dopaminergic activity and is used as a marker of 'central fatigue' during active heat exposure. Significant correlations have consistently been found between PRL and core temperature (T-CORE) during prolonged exercise. There has been no investigation into the relationship between PRL and other key thermoregulatory variables during exercise, such as weighted mean skin (T-SK) and mean body temperature (T-B), heat storage (HS), thermal gradient (T-GRAD), heart rate (HR) and skin blood flow (cutaneous vascular conductance, CVC). Therefore, the aim of this study was to ascertain if a significant relationship exists between PRL and these thermoregulatory variables during prolonged exercise. Nine active male subjects conducted three trials of similar to 60% VO2peak at 70 - 80 rpm for 45 min on a semi-recumbent cycle ergometer at three different ambient temperatures [6 degrees C (Cold), 18 degrees C (Neutral) and 30 degrees C (Hot)] to elicit varying levels of thermoregulatory stress during exercise. Significant differences existed in T-SK, T-B, HS, T-GRAD and CVC across the environmental conditions (p < 0.001). Core temperature (TCORE), HR and PRL were significantly elevated only in Hot (p50.05). Moderate correlations were found for TCORE, TSK, TB, HS, T-GRAD, HR and CVC with post-exercise PRL (p = 0.358 - 0.749). The end-of-exercise < 38.0 degrees C T-CORE responses were not (p = -0.129, p > 0.05) but the > 38.0 degrees C T-CORE responses were (p = 0.845, p < 0.001) significantly related to their corresponding PRL responses. The significant relationships between PRL release and T-SK, T-B, HS, T-GRAD, HR and CVC have extended previous research on T-CORE and PRL release and indicate an association between these thermoregulatory variables, as well as TCORE, and serotonergic/dopaminergic activity during prolonged exercise.