Meeting Abstract

P2.24  Jan. 5  Effects of prenatal steroids on the scalenus muscle of guinea pigs (Cavia porcellus) HELLIE, A.C.**; DEAROLF, J.L.; Hendrix College, Conway, AR; Hendrix College, Conway, AR hellieac@hendrix.edu

Women at risk for preterm deliveries may be treated with prenatal glucocorticoids in order to decrease the risk of respiratory distress syndrome in their infants. These chemicals are known to accelerate fetal lung maturity. However, the effects of prenatal exposure to glucocorticoids on the development of ventilatory muscles are unknown. Corticosteroid treatment has been shown to cause atrophy of the diaphragm and other respiratory muscles in juveniles and adults and a decrease in the percentage of type IIB fibers in the hindlimb muscles of fetal sheep. Because of these findings, we hypothesize that prenatal glucocorticoid treatment will also have some harmful effects on the scalenus, an accessory inspiratory muscle, in the guinea pig. Specifically, we expect to find that in comparison to control fetal muscles, the muscles of treated fetuses will be made up of smaller fibers and contain a smaller percentage of type IIB fibers. To test these hypotheses, we will inject pregnant guinea pigs at 70% gestation with betamethasone (0.5 mg/kg) or sterile water. Twenty-four hours after the second injection, we will euthanize the females and fetuses and collect scalenus muscle samples. Histochemical techniques will be used to determine the fiber-type profiles of the scalenus muscles of treated and untreated fetuses, and the diameters of the muscle fibers will be measured. If the scalenus muscle of treated fetuses demonstrates the hypothesized characteristics, there may be functional consequences of these changes. Two examples include a decreased ability to produce force and a slower contraction speed. These functional problems would lead to a weakened ventilatory system, which would have difficulty responding to any respiratory challenges caused by disease or a poor environment.