Dynamics of myocytes of different types in rat myometrium during pregnancy and early postpartum involution.

Light and electron microscopy and morphometry of rat myometrium revealed 5 morphological types of myometrial smooth muscle cells. Quantitative evaluation of all cytotypes was performed in nonpregnant animals, during normal pregnancy, and during the early postpartum period. Transformation of some cells with nonvacuolated cytoplasm and clear nuclei (type 1) into type 3 cells (with small vacuoles in the cytoplasm), type 4 cells (in a state of balloon degeneration), and type 5 cells (apoptotic bodies) was observed during gestation and early postpartum period.