Meeting Abstract

P1.41  Thursday, Jan. 3  Effects of betamethasone on scalenus muscle development in Cavia porcellus HERROLD, M.L.**; RHOADS, S.K.; HELLIE, A.C.; WEIGAND, K.L.; DEAROLF, J.L.; Hendrix College, Conway, AR herroldml@hendrix.edu

Glucocorticoids, such as betamethasone, have often been administered to pregnant women likely to give birth prematurely in order to accelerate the development of the fetus� organs. Much study has centered on the effects of this treatment on the lungs of fetuses, but little has been concerned with their effects on the muscles associated with breathing. Experiments have found that corticosteroid treatment induces atrophy in a variety of breathing muscles of adult and juvenile rats. It also leads to a loss of fast-twitch fibers in the hindlimb muscles of fetal sheep. To test the effects of betamethasone on the fetal scalenus muscle, pregnant guinea pigs were injected with either betamethasone (0.5 mg/kg) (treated) or with sterile water (control) at 70% gestation. Fiber type profile and fiber diameter of the fetal scalenus were studied. It was expected that fetuses treated with the steroid would have a decreased percentage of fast-twitch fibers, as well as smaller average fiber diameters. The only characteristic that varied significantly between the control and treated fetuses was fast twitch fiber diameter, with the treated animals displaying a smaller fiber diameter (11.2 ± 0.3 µm) than the control animals (12.2 ± 0.5 µm). Apart from this difference, our results suggest that administration of the steroid does not detrimentally affect fetal breathing muscles. However, the proportion of maternal energy invested in each fetus was not investigated and could account for the differences in development between each fetus� breathing muscles in both the control and treated groups. More study should be conducted to determine the relationship between litter size and relative rates of fetal development, so that the effects of the steroid can be quantified more reliably.