Morphological study of the main mechanisms of myometrium involution after repeated pregnancies in mice.

Elimination of "excessive" myocytes and their structures during involution of the myometrium after the first and third pregnancies was realized by clasmocytosis (eliminating the greatest volume of myocyte cytoplasm fragments), apoptosis, and necrosis (equal percentage by volume). In contrast to the first pregnancy, involution after the third one was not over by day 10 because of inhibited elimination of functionally lost myocytes by necrosis and apoptosis mechanisms. Presumably, this was caused by slower hydrolysis of apoptotic bodies by macrophages. The concentration of macrophages in the myometrium on day 10 of the involution period in females after the third delivery was 4-fold higher than in intact mice and in females after the first delivery during the same period.