Trypsin-like activity in the vaginal epithelial cells of the rat

Rat vaginal epithelial cells have trypsin-like activity as shown by the formation of a colored product when the cells are incubated with alpha-N-methyl alpha-N-toxyl-L-lysine beta-naphthol ester and hexazotized pararosanilin. This enzyme activity in vaginal smears is maximal at proestrus, i.e., the day in the 5-day estrus cycle when plasma estrogen is maximal. Only the rounded nucleated epithelial cells present at late diestrus, proestrus and early estrus demonstrate the trypsin-like enzyme activity. These are the cells that stain blue in the Papanicolaou method. Preincubation of cell suspensions with the serine protease inhibitor, p-nitrophenyl p-guanidino benzoate, prevented the enzyme staining reaction, further demonstrating the trypsin-like nature of the cellular enzyme. The advantages of this enzyme staining technique over the fibrin plate method for the demonstration of trypsin-like enzymes in cells are increased resolution and ability to show trypsin inhibitor effects.