Meeting Abstract

148.5  Monday, Jan. 7  The effect of prenatal steroids on citrate synthase activity in the fetal guinea pig scalenus muscle BUTLER, M.R.*; 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. In this study, the effect of betamethasone, a glucocorticoid, on the activity of the oxidative enzyme citrate synthase (CS) in the scalenus muscle of fetal guinea pigs will be examined. Previous histological research demonstrated that NADH (oxidative enzyme) concentrations were greater in the scalenus muscles of betamethasone-treated guinea pig fetuses. Thus, we hypothesize that CS activity will be greater in the muscles of fetal guinea pigs treated with betamethasone compared with control fetuses. Pregnant guinea pigs were injected with either betamethasone (0.5 mg/kg) or sterile water twice a week, 24-hours apart, at 65%, 75%, and 85% gestation. Muscles samples were collected, homogenized, and diluted to a predetermined optimal dilution factor with buffer. A reaction mixture (50 mM imidazole, 0.25 mM DTNB, 0.4 mM acetyl CoA, and 0.5 mM oxaloacetate, pH 7.5 at 37˚C) was added, and the maximum reaction rate (Vmax) of CS was measured with a microplate reader at 412nm. The Vmax values were converted to units of enzyme activity (µmol/min·g wet muscle mass), and the average CS activities of the control and treated muscles were compared. If our hypothesis is supported, infants treated with glucocorticoids could potentially have higher oxidative capacities in their ventilatory muscles than their untreated counterparts. This change would lead to greater fatigue resistance and allow treated infants to better respond to ventilatory challenges.