Endochondral bone growth during early pregnancy compared with pseudopregnancy in rats.

There are physiological and skeletal changes that occur during pregnancy to accommodate the increased calcium needs of late pregnancy and lactation in the rat. Endochondral bone growth is accelerated during early to midpregnancy, but the endocrine basis of this is not clear. The purpose of this study was to define the role, if any, of placental factors in changes in endochondral growth by comparing changes that occur during pregnancy with pseudopregnancy in the rat. Many hormones change during pseudopregnancy, except placental hormones (e.g., placental lactogens) because a placenta is lacking. Rates of endochondral growth were increased during pregnancy and pseudopregnancy compared to age-matched, unmated controls. There were also increases in body weight in both pregnant and pseudopregnant animals. Since the observed changes occur in both pregnant and pseudopregnant animals, this indicates that endocrine factors other than those secreted by placenta are involved in increased growth during early pregnancy.