EFFECT OF MENSTRUAL PHASE ON NEUROENDOCRINE RESPONSE FOLLOWING PROGRESSIVE CYCLE EXERCISE

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1085 Limited research has been done on effects of menstrual phase on pituitary and adrenal hormonal responses to exercise. Proenkephalin peptide F (PF) is a neurohormone co-packaged with epinephrine in chromaffin cells in the adrenal medulla. Progressive cycle exercise in women has previously shown no change in PF concentrations, without equating for menstrual phase (FP, Follicular phase; LP, Luteal phase). Eight eumenorrheic, untrained women (26.8±1.2y; 59.4±3.2kg; 163.4±2.9cm; 25.2±1.4%BF; 44.8±1.1 ml/kg/min) participated in a study examining the effects of menstrual cycle phase on neuroendocrine responses following a progressive cycle ergometer exercise to exhaustion. Menstrual history was recorded with validation of phase via serum estradiol and progesterone. Each subject cycled at a constant 60 rpm with increasing intensity 1Kp every 2 min until volitional fatigue. HR, BP, and RPE were recorded every 2 min. Exercise was randomized between menstrual phases. Blood was drawn pre-exercise and 0, 15, and 30 min post-exercise for analysis of GH, IGF-I, PF, and Lactate (LA).. There was no significant (p≤0.05) effect of phase or exercise on HR response and exercise time to fatigue and LA and PF levels. Independent of phase, exercise increased (above baseline) LA 0 and 15 min post-exercise. There was no effect of phase on GH and IGF-I. Main effects of exercise on GH increased (above baseline) 0, 15, and 30 min post-exercise in both phases. IGF-I decreased (below baseline) 0 min post-exercise in both phases with return to baseline levels by 15 min post-exercise. IGF-I decrease could indicate an acute tissue sequestering response. Due to the higher physical stress levels with progressive cycle exercise to fatigue and the cosecretory nature of the chromaffin cells in the adrenal medulla, the higher epinephrine concentrations in untrained women (Triplett-McBride et al, Peptides, 1998) seem to predominate the secretory mechanisms, thus limiting the responsiveness of PF to this exercise.