Meeting Abstract

P1.36  Monday, Jan. 4  The effects of prenatal steroids on the rectus abdominus muscle in fetal guinea pigs WARSINSKE, H.C.**; GORDON, V.K.; PREHODA-WYERS, M.M.; DEAROLF, J.L.; Hendrix College, Conway, AR warsinskehc@hendrix.edu

To increase the chances of a successful premature birth, an expectant mother is injected with glucocorticoid steroids in order to speed the development of her fetus’s lungs. Betamethasone is one example of a glucocorticoid, and its long term effects on fetal lung tissue are relatively well understood. However, the effects of this steroid on a fetus’s breathing muscles are not well known. We will be examining how exposure to betamethasone influences the number, size, and type of muscle fibers in the rectus abdominus, an expiratory muscle of fetal guinea pigs (Cavia porcellus). Our hypothesis is that the administration of these steroids to expectant mothers will cause a decrease in the number of type IIa fast twitch fibers and atrophy, such that the fibers in the muscles of treated fetuses will be smaller than those in untreated specimens. This hypothesis is based on findings of the effects of these steroids on fetal sheep hindlimb muscles and adult rodent breathing muscles. Pregnant guinea pigs will be injected with betamethasone (0.5 mg/kg) or sterile water 65%, 75%, and 85% gestation. Fetal rectus abdominus samples will be collected and prepared for immunohistochemistry, which will be used to identify the different fiber types present. Scion Image will be used to collect data on fiber number, diameter, and staining density. If our hypothesis is supported, babies exposed to prenatal steroids could have decreased ventilatory rates, as a result of decrease in the number of type IIa fibers. Atrophy would also mean smaller, less effective muscles.