Serum prolactin responses to duathlon performance following pre-exercise dietary manipulation

Serum prolactin (PRL) concentrations become elevated following a low carbohydrate diet as well as exercise which elicits significant rises is core temperature. The effect of pre-exercise dietary manipulation on PRL responses to exercise, which significantly elevates core temperature, has not been scrutinised. Nine male subjects of mean (SD) age 28.6 (5.9) years, body mass 76.8 (8.5) kg, height 1.80 (0.7) m, and VO2max 4.8 (0.6) l.min-1 completed three laboratory simulated duathlon time trials consisting of a 5 km run, 30 km cycle, and a further 5 km run. Each time trial was separated by at least 1 one week. Subjects fasted overnight before the duathlons and were randomly given isoenergetic meals (3998 (2.2) kJ) 3.5 h before the start of exercise. The meals consisted of predominantly low carbohydrate (LCHO) or high carbohydrate (HCHO) macronutrient components, or a fasting (F) condition, in which subjects ate nothing. Rectal temperature was used as an index of core temperature (Tc). Venous blood samples were taken immediately prior to and following the final running stage, in order to determine serum prolactin responses. The analysis of PRL was performed using enzyme-linked immunosorbent assay. A general linear model ANOVA, with repeated measures was used to determine significant differences (P<0.05). Means were compared using the Bonferroni confidence interval. Relationships between variables were made using Persons correlation coefficient. PRL was unaffected prior to exercise by the meal strategies (P>0.05), but significant increases were observed following the completion of all the time trials (P<0.05). There were no significant differences in Tc as a result of the meal strategies, but the performance of the time trials caused significant increases in Tc (P<0.05). PRL was significantly correlated to Tc (r=0.81). Overall mean speed throughout the duathlons was used as an indicator of performance, but there were no significant differences as a result of the dietary conditions (6.6 (0.4) m s-1, 6.5 (0.4) m s-1, 6.4 (0.5) m s-1) for F, LCHO and HCHO, respectively (P>0.05). These data suggest that following acute dietary manipulation, the PRL response to strenuous exercise is unaffected, and post exercise elevations are likely to be a consequence of the rise in Tc.