Meeting Abstract

P2.161  Saturday, Jan. 5  Assessment of the oxidative capacity of the rectus throracis muscle in betamethasone treated fetuses WALKER, R.A.*; DEAROLF, J.L.; RICHMOND, J.P.; Hendrix College, Conway, AR ; Univ. of North Florida, Jacksonville, FL walker@hendrix.edu

Multiple doses of the prenatal steroid, betamethasone, accelerate the lung development of premature babies. However, the effects of betamethasone on the development of ventilatory muscles are unclear. Previous histochemical research in our laboratory indicated that a multi-course exposure to betamethasone did not affect the percentages of highly oxidative slow- and fast-twitch fibers in an accessory ventilatory muscle. However, our histochemical analyses did not allow us to compare the actual oxidative enzyme concentrations in the steroid-treated and control muscles. Thus, additional biochemical analyses that allow us to quantify oxidative enzyme concentrations are necessary to support our conclusion that betamethasone does not affect the oxidative capacity of ventilatory muscles. Samples of the rectus thoracis, an accessory ventilatory muscle, were collected from fetal guinea pigs that were exposed to multiple doses (2 injections per week at 65%, 75%, and 85% gestation) of betamethasone or sterile water prior to collection of muscle samples. Extracts of each fetal muscle were prepared and analyzed for their citrate synthase (CS) activities under the following conditions: 50 mM imidazole, 0.25 mM DTNB, 0.4 mM acetyl-CoA, and 0.5 mM oxaloacetate, pH 7.5 at 37°C. If the average CS activities of the control and treated rectus thoracis muscles are similar, these data would support our hypothesis that betamethasone does not have a significant effect on the oxidative capacities of the rectus thoracis muscle. Thus, premature babies treated with betamethasone will have similar oxidative capacities in their ventilatory muscles and will not be better prepared to sustain ventilation than babies who are not exposed to prenatal steroids.