Meeting Abstract

P1.125  Sunday, Jan. 4  Does fetal betamethasone exposure increase the potential for fatigue in the scalenus muscle of guinea pigs (Cavia porcellus)? DORNHOFFER, T.M.**; WEIGAND, K.L.; DEAROLF, J.L.; Hendrix College, Conway, AR dornhoffertm@hendrix.edu

Betamethasone is a corticosteroid, a group of drugs often used to reduce mortality in premature infants. Its effects on breathing muscle development, however, are not well known. Studies have shown that similar corticosteroids significantly reduce the oxidative capacities of adult diaphragm muscle. Based on these studies, we hypothesize that betamethasone will significantly reduce the oxidative capacity of the scalenus. This reduction could have significant ramifications for a fetus exposed to such steroids, reducing the fatigue capacity of the ventilatory muscles. A secondary goal of this project was to see if differences in oxidative capacity can be used to subtype the fast-twitch fibers in the fetal muscles. Guinea pigs were injected with betamethasone (0.5 mg/kg maternal weight) or sterile water twice a week (24 hours apart) for three weeks. After a gestation period of 59 days, scalenus samples were obtained from treated and control fetuses and prepared for muscle histochemistry. Sections of the muscle samples were stained for their NADH-tetrazolium reductase activities to quantify oxidative capacity and counterstained with eosin to highlight fiber margins. Additional serial sections were stained with slow antibodies to locate slow fibers within the sections. Images of stained sections were captured and analyzed using Scion Image, and the mean staining density of a representative sample of fibers was measured. At the time of writing, data collection is insufficient to determine the effects of betamethasone on oxidative capacity. Preliminary data indicate the presence of multiple peaks within a mean density plot of staining densities of the fast-twitch fibers, which suggests that oxidative capacity can be used to subtype these fibers.