Meeting Abstract

P2.131  Monday, Jan. 5  Influence of betamethasone on the fast-twitch fibers of the external abdominal oblique in fetal guinea pigs (Cavia porcellus) MARSHALL, S.L.**; WEIGAND, K.L.; DEAROLF, J.L.; Hendrix College, Conway, AR marshallsl@hendrix.edu

Glucocorticoid steroids are used to accelerate the development of various organs in fetuses before premature delivery. In the present study, the possible negative ramifications of the use of betamethasone, a glucocorticoid, on the expiratory external abdominal oblique muscle were considered. We hypothesize that exposure to betamethasone will result in a significant amount of muscle atrophy and significant decrease in the percentage of fast-twitch fibers in the external abdominal oblique. To test these hypotheses, pregnant guinea pigs were injected with betamethasone (0.5 mg/kg) or sterile water at 65%, 75%, and 85% gestation. Samples of the external abdominal oblique were then collected from all fetuses, cut using a cryostat, and stained for myosin ATPase activity. Images of the stained muscle sections were taken and fiber percentages were calculated. Scion Image was used to measure fiber diameter as well. The external abdominal oblique aids in a fetus ability to exhale carbon dioxide. In periods of stress, the fast-twitch fibers are recruited to exhale at a faster pace than normal conditions. A decrease in number or atrophy of the fast-twitch fibers would impair this muscles ability to contract with the same speed as a normal non-treated muscle. These side effects would hinder a preterm infants ability to cope with periods of respiratory distress. This inability to adapt could prove damaging or life threatening to the infant.