P1.163 Wednesday, Jan. 4 Effects of betamethasone on myosin light chain expression of fetal Cavia porcellus intercostals PRINCE, S.C.**; WALKER, R.A.; DEAROLF, J.L.; Hendrix College, Conway, AR email@example.com
Corticosteroids stimulate lung development in growing fetuses. These benefits of corticosteroids are being utilized in modern medicine to attempt to increase fetal survival in mothers that are expected to go into pre-term labor. Corticosteroids are known to improve lung function; however, less is known about their effects on the ventilatory system as a whole, particularly in regards to breathing muscles. Previous studies in our lab have shown that a multi-course exposure to betamethasone, a corticosteroid, leads to changes in myosin heavy chain (MHC) isoform expression in fetal guinea pig intercostal muscles. To more fully understand the functional consequences of prenatal exposure to corticosteroids, it is necessary to also examine the effects on myosin light chain (MLC) expression in fetal guinea pigs, because both MLC and MHC regulate the rate of muscle contraction and may be affected by steroid treatment. Pregnant guinea pigs were injected twice weekly, twenty-four hours apart at 65%, 75%, and 85% gestation. Twenty-four hours after the last betamethasone or sterile water injection, the females were euthanized, and samples of the fetal intercostal muscles were collected. Extracts of the fetal muscle samples were prepared and separated in SDS-polyacrylamide (12%) gels for ∼3 hours (30 mA/gel) at 18° C. These gels were silver stained, and Scion Image software was used to determine the proportions of MLC1 and MLC2 relative to actin in the treated and control intercostal muscles. Based on any changes we see in MLC1 and MLC2 expression in the treated muscles, we will be able to predict the effects on ventilatory system function in premature newborns.