TProlactin Responses, Menstrual Cycles, and Body Composition of Women Runners*

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Abstract
Fourteen young women with normal menses participated in an endurance running program to investigate the effects of physical training on menstrual function, plasma PRL, and body composition. Body composition, measured by hydrostatic weighing, and PRL (basal and TRH-stimulated) were determined initially and after each subject had increased her weekly mileage by 30 miles (Δ30) and 50 miles (Δ50). Mean (±SEM) total body weight did not change, but the subjects became significantly leaner (relative fat, 25.5 ± 1.3% at baseline vs. 22.4 ± 0.9% at A50; P < 0.02). Thirteen women developed menstrual changes (mainly oligomenorrhea), but not amenorrhea. Mean (±SEM) unstimulated PRL levels were 16.8 ± 3.1,16.9 ± 2.4, and 11.5 ± 2.1 ng/ml at baseline, Δ30, and Δ50,respectively (P < 0.03 at A50 compared to baseline and A30). Mean (±SEM) integrated TRH-stimulated PRL responses increased from 5002 ± 462 ng/ml·min at baseline to 5748 ± 609 ng/ml-min at A30 and 6535 ± 552 ng/ml · min at A50, and were significantly different from one another (F = 4.01; P < 0.04). Endurance training, without total body weight loss or extreme leanness, results in frequent menstrual dysfunction. Other authors have shown that young female athletes have an increased PRL response to acute exercise compared to nonathletes. One mechanism responsible for menstrual dysfunction in endurancetrained women may be frequent and exaggerated PRL responses to exercise and other stimuli.