Exercise augments the nocturnal prolactin rise in exercise-trained men

Objective: The objective of this study was to profile over a 24 h period the prolactin responses of exercise-trained men on a day involving rest with no exercise in comparison to a day involving exercise training sessions. Methods: This is a quasi-experimental design study using repeated measures determination of 24 h prolactin responses in exercise-trained men (n = 16; age = 27.3 +/- 3.3 years (mean +/- standard deviation)). Blood samples were taken hourly over a 24 h period on a day involving two intensive exercise training sessions (ED), and on a separate control day (CD) with no exercise activity. The order of the ED and CD was randomized. Physical activity and diet were controlled and replicated for the ED and CD. Blood specimens were handled, prepared and analyzed utilizing appropriate standard clinical practices. The data were analyzed with the Friedman analysis of variance and Nemenyi post hoc statistical procedure for repeated measures. Results: On the CD, prolactin displayed a typical circadian rhythm with daytime values of the hormone being less than the nocturnal rise once sleep had begun (p < 0.05; 16:00-20:00 h > all other times). On the ED, prolactin responses were noticeably different from those of the CD. The morning and afternoon exercise sessions included significant increases in prolactin immediately at the end of the exercise sessions, being greater than corresponding CD time points (p < 0.01; 01:00 h and 10:00 h); also for the second hour (2 h) following the morning exercise session. On the ED there was a displayed circadian nocturnal response in the hormone with 16:00-24: 00 h being elevated above the all nonexercise effected values for that specific day (p < 0.01). Finally, the ED nocturnal elevation for prolactin for 16:00-24:00 h was significantly greater than the same respective hours on the CD (p < 0.05). Conclusion: Findings clearly demonstrated that nocturnal prolactin responses are augmented in exercise-trained men on days when they perform exercise. The mechanisms inducing this adaptive response are unclear but warrant further investigation.