![]() Uterine smooth muscle undergoes dramatic physiological adaptations during the course of pregnancy. The restriction of the hypertrophy to cells within the gravid horn suggests that it may be a response to the biological mechanical stretch of uterine walls by the growing fetus(es) and placenta(s). A significant increase in SMC volumes was detected in the gravid uterine horn as compared with the corresponding empty horn of unilateral term pregnant animals (day 22, mean cell volume 1114 vs 361 μm 3, P<0.05), indicating the effect of uterine occupancy. The stereological analysis revealed that the dramatic increase in myometrial growth seen during late gestation (d19–22) is due to a threefold increase in the size of uterine myocytes. Anti-caveolin-1 immunostaining was used to clearly delineate SMC boundaries. Uterine tissues were collected from nonpregnant Wistar rats, as well as from gravid and nongravid horns of unilaterally pregnant animals on gestational days (d) 8 (early gestation), 14 (mid-gestation), 19 (late gestation), 22 (term), and 4 days post partum. We employed a stereological approach to calculate the average cell volumes of uterine myocytes through diameter measurements using the Stereoinvestigator statistical software. This study sought to test the hypothesis that increase in myometrial growth seen during late pregnancy is due to SMC hypertrophy caused by mechanical stretch of uterine tissue by a growing fetus(es) by providing direct measurements of individual SMC size. In early pregnancy, uterine growth is due to hyperplasia of uterine smooth muscle cells (SMCs) within the myometrium however, the major component of myometrial growth occurs after mid-gestation. The adaptive growth of the uterus is a critical event that involves changes in cellular phenotypes throughout pregnancy. ![]()
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January 2023
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