Meeting Abstract

P2.26  Jan. 5  Effects of betamethasone on the development of an expiratory muscle in guinea pigs (Cavia porcellus) THOMPSON, K.E.**; DEAROLF, J.L.; Hendrix College, Conway, AR; Hendrix College, Conway, AR thompsonk@mercury.hendrix.edu

Respiratory disease is a major condition affecting preterm neonates. One way in which this problem is treated is with the injection of prenatal glucocorticoids, which stimulate structural lung development and initiate pulmonary surfactant production. No studies have currently been published on the effects of prenatal glucocorticoids on the development of the ventilatory muscles. However, these steroids have been shown to cause atrophy in the breathing muscles of adults and juveniles and a decrease in the percentage of type IIB fibers in the hindlimb muscles of fetal sheep. Therefore, we hypothesize that the development of the rectus abdominus, an expiratory muscle in the guinea pig, will be detrimentally affected by exposure to prenatal glucocorticoids. Specifically, we expect to see smaller fibers and less type IIB fibers in the muscles of treated fetuses in comparison to control muscles. To test these hypotheses, we will inject pregnant guinea pigs at 70% gestation with betamethasone (0.5 mg/kg) or a control (sterile water). Twenty-four hours after the second injection, the females and fetuses will be put down and samples of the rectus abdominus will be collected. We will then use histochemistry to determine the fiber-type profiles of the rectus abdominus muscles of treated and control fetal guinea pigs. We will also measure the diameters of any identified fiber types. If exposure to prenatal glucocorticoids leads to the hypothesized changes in morphology, the rectus abdominus of treated fetuses may not be able to produce as much force or contract as quickly as this muscle in control fetuses. Thus, this muscle may have difficulty responding to any challenges placed on the ventilatory system by illness or disease.