Exercise-Induced Dissociation of the Blood Prolactin Response in Young Women According to their Sports Habits

Abstract

To evaluate the blood prolactin (PRL) response to a standardized physical exercise imposed on young women with different sports habits, twelve young girls (mean age ± S.E. = 21.9 ± 1.8) without any gynecologic history were divided into two groups according to the presence (+ SH) or the absence (-SH) of a past and present sport history (N = 7 & 5, and O₂ max = 43.6 & 37.6 ml/kg/min for group +SH and -SH, respectively; Student's test on O₂ max revealed a non-significant mean difference). On the 7th day of her menstrual cycle, each subject was submitted to a 30-min period of bicycle work at 75 % of her O₂ max. Blood was sampled from an ante-brachial vein before, during and after the work period. While the work load was unable to elicit any significant change in blood PRL of group -SH, that same load, when imposed on +SH students, evoked a very characteristic response. Indeed, after 15 min of ergocycling, their blood PRL had increased significantly (P < .02); after 30 min of work, the blood PRL level had doubled the one observed upon initiation of work (+103.2 %; P < .03). During the recovery period, blood PRL of that same +SH group rapidly returned toward its basal values. Even though these marked increments in blood PRL seem unable to significantly disturb the established menstrual cycle of these post-pubescent girls, they could most probably furnish an explanation to Malina's findings of a significantly (P < .001) delayed menarche in athletic adolescents. In fact, repeated heavy physical exercises by the latter with concomitant PRL increments could create a PRL impregnation on the maturing ovary sufficient to delay any FSH follicle-stimulating action, a transient amenorrhic condition somewhat similar to the one observed in the nursing mother.