title: The prolactin responses to active and passive heating in man.
abstract: The aim of this study was to compare the prolactin and blood pressure responses at identical core temperatures during active and passive heat stresses, using prolactin as an indirect marker of central fatigue. Twelve male subjects cycled to exhaustion at 60% maximal oxygen uptake (VO2peak) in a room maintained at 33 degrees C (active). In a second trial they were passively heated (passive) in a water bath (41.56 +/- 1.65 degrees C) until core temperature was equal to the core temperature observed at exhaustion during the active trial. Blood samples were taken from an indwelling venous cannula for the determination of serum prolactin during active heating and at corresponding core temperatures during passive heating. Core temperature was not significantly different between the two methods of heating and averaged 38.81 +/- 0.53 and 38.82 +/- 0.70 degrees C (data expressed as means +/- s.d.) at exhaustion during active heating and at the end of passive heating, respectively (P > 0.05). Mean arterial blood pressure was significantly lower throughout passive heating (active, 73 +/- 9 mmHg; passive, 62 +/- 12 mmHg; P < 0.01). Despite the significantly reduced blood pressure responses during passive heating, during both forms of heating the prolactin response was the same (active, 14.9 +/- 12.6 ng ml(-1); passive, 13.3 +/- 9.6 ng ml(-1); n.s.). These results suggest that thermoregulatory, i.e. core temperature, and not cardiovascular afferents provide the key stimulus for the release of prolactin, an indirect marker of central fatigue, during exercise in the heat.
authors.affiliation: Research Institute for Exercise and Environmental Medicine, Liverpool John Moores University, Liverpool L3 2ET, UK. davidlow@texashealth.org
authors.forename: David
authors.initials: D
authors.lastname: Low
authors.forename: Alison
authors.initials: A
authors.lastname: Purvis
authors.forename: Thomas
authors.initials: T
authors.lastname: Reilly
authors.forename: N Tim
authors.initials: NT
authors.lastname: Cable
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001831:Body Temperature; D002302:Cardiac Output / Q000502:physiology; D005221:Fatigue / Q000503:physiopathology; D005542:Forearm; D006339:Heart Rate / Q000502:physiology; D018882:Heat Stress Disorders / Q000097:blood / Q000503:physiopathology*; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D008297:Male; D011388:Prolactin / Q000097:blood*; D012867:Skin / Q000098:blood supply; D013318:Stroke Volume / Q000502:physiology
chemical_list: D011388:Prolactin