Cell kinetic study of the endometrium by nonisotopic in situ hybridization for histone H3 messenger RNA and immunohistochemistry for Ki-67 and for estrogen and progesterone receptors.

We investigated the cell kinetics of the endometrium in hysterectomy specimens taken for leiomyoma from 22 women with regular ovulatory menstrual cycles. Formalin-fixed, paraffin-embedded tissue sections were examined for proliferating activity using histone H3 messenger RNA in situ hybridization (H3 mRNA-ISH) and immunostaining for the Ki-67 antigen. The relationship of the proliferative activity of endometrial cells to the immunohistochemical expression of the estrogen receptor (ER) and the progesterone receptor (PR) was also examined. During the menstrual cycle, H3 mRNA expression was observed in both the epithelial cells and the stromal cells of the endometrium. In the functional layer, the labeling indices for H3 mRNA (H3 mRNA-LIs) in the epithelial cells peaked in the late proliferative phase, decreased sharply in the early secretory phase, and remained unchanged thereafter. On the other hand, H3 mRNA-LIs of stromal cells displayed two peaks: one in the midproliferative phase and the other in the late secretory phase, the former peak being the greater. In the basal layer, epithelial cells and stromal cells showed low H3 mRNA-LIs and no significant variation throughout the menstrual cycle. The H3 mRNA-LIs correlated well with the Ki-67-LIs and were lower than the corresponding Ki-67-LIs. The regression coefficient (H3 mRNA-LIs against the Ki-67-LIs) was 0.33 for epithelial cells and 0.49 for stromal cells, suggesting that the cell cycle time was longer for epithelial cells than for stromal cells. The proliferative activity of endometrial cells showed close relationships with the expressions of ER and PR in the endometrium. When used in combination with other proliferative markers in paraffin-embedded tissue sections, H3 mRNA-ISH could open broader perspectives on the cell kinetics of the endometrium.