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De Crée, Carl, Peter Ball, Bärbel Seidlitz, Gerrit Van Kranenburg, Peter Geurten, and Hans A. Keizer. Plasma 2-hydroxycatecholestrogen responses to acute submaximal and maximal exercise in untrained women. J. Appl. Physiol. 82(1): 364–370, 1997.—Exercise-induced menstrual problems are accompanied by an increase in catecholestrogen (CE) formation. It has been hypothesized that hypoestrogenemia may be secondary to an increased turnover from estrogens to CE, which then may disrupt luteinizing hormone release. In addition, the strong affinity of CE for the catecholamine-deactivating enzyme catechol- O-methyltransferase (COMT) has led to speculations about their possible role in safeguarding norepinephrine from premature decomposition during exercise. We investigated whether acute exercise on a cycle ergometer produces any changes in CE homeostasis. Nine untrained eumenorrheic women (body fat, 24.8 ± 3.1%) volunteered for this study. Baseline plasma CE averages for total 2-hydroxyestrogens (2-OHE) were 218 ± 29 (SE) pg/ml during the follicular phase (FPh) and 420 ± 58 pg/ml during the luteal phase (LPh). 2-Methoxyestrogens (2-MeOE) measured 257 ± 17 pg/ml in the FPh and 339 ± 39 pg/ml in the LPh. During incremental exercise, total estrogens (E) increased, but 2-OHE and 2-MeOE levels did not significantly change in either phase. The 2-OHE/E ratio (measure of CE turnover) decreased during exercise in both menstrual phases, whereas the 2-MeOE/2-OHE ratio (correlates with COMT activity) did not significantly change. These findings suggest that there is insufficient evidence to conclude that brief incremental exercise in untrained eumenorrheic females acutely produces increased CE formation.