Lacrimal fluid peroxidase activity during the menstrual cycle

Purpose. The aim of this work was to investigate peroxidase activity in hum an tears during the various phases of the menstrual cycle. For comparative purposes saliva was also examined. Methods. Tear fluids and saliva from 10 healthy volunteers 23-41 years of a ge (mean: 28.2 years), with regular menstrual cycles were sampled for the d uration of at least two complete cycles. Menstrual cycles and ovulation per iods were evaluated by measuring morning body temperature and hormone level s in plasma and urine. Unstimulated tears and unstimulated saliva were coll ected in the morning every two days. Peroxidase activity was monitored acco rding to the 5,5'-dithiobis, 2-nitrobenzoic acid thiocyanate (Nbs-SCN) meth od and the protein content was determined by the Bradford method. Results. Peroxidase activity in tears, expressed as U/mL, was significantly (p < .05) higher during the preovulatory and luteal phases with respect to the menses, whilst total protein content remained almost unchanged through out all phases. A positive correlation was found between lacrimal fluid per oxidase activity and 17 beta-estradiol plasma levels (p < .001). Salivary p eroxidase activity did not show such estrogen-related changes. Conclusions. Our findings report cyclic variations in peroxidase activity i n human tears during the menstrual cycle. Such cycling seems to reflect var iations of 17 beta-estradiol plasma levels. These results suggest that a re gulation of lacrimal fluid peroxidase by 17 beta-estradiol could be one pos sible cause for the female gender predilection in some ocular diseases, suc h as keratoconjunctivitis sicca.