Meeting Abstract

P1.38  Monday, Jan. 4  Prenatal steroids: do they affect the development of the guinea pig rectus thoracis muscle? CHUGHTAI, A.**; BREWINGTON, A.K.; PREHODA-WYERS, M.M.; DEAROLF, J.L.; Hendrix College, Conway, AR chughtaiaa@hendrix.edu

Glucocorticoids are used to accelerate the lung development of premature babies. The effects of glucocorticoids on breathing muscles are unknown, however. To determine the effects of these steroids on the accessory inspiratory rectus thoracis muscle, pregnant guinea pigs were injected with betamethasone, a glucocorticoid. It is known that this steroid stops the proliferation of muscle fibers, causing the differentiation of these cells to begin earlier. In the case of the guinea pig rectus thoracis, the last fibers to differentiate and, therefore be affected by steroid exposure, are the type IIA fibers. Thus, we hypothesize that betamethasone exposure will cause the IIA fibers in the rectus thoracis to be reduced in number and size. Betamethasone was injected at 65%, 75%, and 85% gestation of the pregnant guinea pigs. Samples of the fetal rectus thoracis were collected, sectioned, and antibody stained to distinguish between the different fiber types. Digital images of the stained muscles were collected, and Scion Image was used to analyze fiber number and diameter. The percentages of type IIA fibers in the muscles of treated and control fetuses were compared to determine if the treated muscles had less of these fibers. When fetuses are exposed to glucocorticoids, the inspiratory muscle fibers may be reduced in number and size. These changes could cause the inspiratory muscles of premature babies to have a reduced ability to produce the amount of force needed to survive outside the womb, in comparison to unexposed babies.