Meeting Abstract

50.5  Sunday, Jan. 5 11:15  Effects of prenatal glucocorticoids on the fetal guinea pig scalenus muscle BUTLER, M.R.*; CHUGHTAI, A.; RILEY, L.A.; WALKER, R.A.; DEAROLF, J.L.; RICHMOND, J.P.; Hendrix College, Conway, AR; Univ. of North Florida, Jacksonville, FL butlermr@hendrix.edu

Glucocorticoids are commonly administered to women considered at risk for premature birth to speed up fetal lung development and reduce infant mortality. Although these steroids aid lung development in preterm infants, their effects on ventilatory muscles are not well documented. Studies in our laboratory have found an increased proportion of type IIA fast-twitch fibers and increased IIA and IIX fiber diameters in rectus thoracis muscles of fetal guinea pigs exposed to prenatal steroids. In addition, we have discovered higher concentrations of NADH in the fibers of the scalenus muscles of steroid-treated fetuses, suggesting these muscles have a higher oxidative capacity. Thus, we hypothesized that fetal scalenus muscles exposed to prenatal steroids will exhibit elevated proportions of IIA fibers, increased fast-twitch fiber diameters, elevated citrate synthase activity, and increased myoglobin expression. To test these hypotheses, pregnant guinea pigs were injected with either betamethasone, a glucocorticoid, or sterile water twice a week, twenty-four hours apart, at 65%, 75%, and 85% gestation. Fetal muscle samples were collected and prepared for immunohistochemistry or biochemical analyses. If increased fiber proportions, larger fiber diameters, higher oxidative enzyme activity levels, and higher levels of myoglobin expression are found in treated individuals, these findings would suggest that treated scalenus muscles will produce greater contractile forces and have greater fatigue resistance, which may be demonstrated through physiological testing. These improved functional abilities would allow treated premature infants to better cope with ventilatory challenges when compared to their untreated counterparts.