Plasminogen activator in vaginal smears during the menstrual cycle

A cytologic staining technique in which the reaction produces an insoluble colored precipitate at the site of trypsin-like proteolysis was applied to human vaginal smears, taken daily over six menstrual cycles. The day of urinary LH surge for each cycle was determined. The enzyme action, namely hydrolysis by plasminogen activator, is confined mainly to intermediate squamous cells. The number of cells stained by the enzyme method reaches a maximum three days prior to the LH surge, whereas the maximum in karyopyknosis occurs close to or at the day of LH surge. The enzyme staining method can thus be used when anticipation of ovulation by about 4 days is needed. No immediate fixation is required prior to the enzyme staining.