Meeting Abstract

P3.44  Thursday, Jan. 6  The effect of glucocorticoids on the oxidative capacity of the fetal guinea pig rectus abdominus BISSELL, J.A.*; PREHODA-WYERS, M.M.; DEAROLF, J.L.; Hendrix College, Conway, AR bissellja@hendrix.edu

Glucocorticoids have been used clinically to help the development of premature fetuses. Fetuses are exposed to these steroids so that their lungs will be able to develop before they are born. However, the effects of these steroids on breathing muscle development were not well known. Work in our laboratory has shown that exposure to prenatal betamethasone increases the oxidative capacities of the fibers in the guinea pig scalenus. Thus, our findings suggest that prenatal glucocorticoids accelerate muscle development. In this experiment, we will determine the effects of prenatal steroids on the rectus abdominus (RA), an accessory expiratory muscle of the guinea pig. We hypothesize that the fibers in the treated muscles will have higher oxidative capacities than fibers in the control muscles. To test this hypothesis, pregnant guinea pigs were injected with betamethasone (at 65%, 75% and 85% gestation) or sterile water, and samples were collected from fetal RA muscles. Serial sections of the samples were then stained for their NAD-tetrazolium reductase and myosin ATPase activities, and digital images were taken of the stained sections. Images were analyzed with Scion Image, and the staining densities of a representative sample of slow- and fast-twitch fibers for each fetal muscle were measured. The mean staining densities were converted to Z-scores, which were then used to calculate the proportions of light- and dark-staining slow- and fast-twitch fibers. If the treated RA muscles have more fibers with high oxidative capacities (percent dark-staining), these muscles have reacted positively to the steroid, producing the hypothesized result. Thus, premature infants that are exposed to betamethasone would have more mature RA muscles, which may better support breathing.