Meeting Abstract

28.2  Wednesday, Jan. 5  The effects of betamethasone on myosin expression patterns of fetal Cavia porcellus hindlimb and ventilatory musculature SCHROEDER, J.R.*; PREHODA-WYERS, M.M.; DEAROLF, J.L.; Hendrix College schroederjr@hendrix.edu

When pregnant women are likely to give birth prematurely, glucocorticoids are administered to accelerate the development of fetal organs. Studies indicate glucocorticoids switch the cell cycle from proliferation to differentiation. In muscles, differentiation includes changes in myosin heavy chain expression. Specifically, fetal myosin decreases in expression and is replaced by adult fast isoforms: neonatal, IIA, and IIX. Thus, we hypothesize that the hindlimb and ventilatory muscles of Cavia porcellus exposed to glucocorticoids will display more adult fast myosin isoforms than control muscles. To test this hypothesis, pregnant guinea pigs were injected with either betamethasone or with sterile water at 65%, 75%, and 85% gestation. The fetal myosin profile was assessed with the use of 7% acrylamide, 30% glycerol gels ran at 275V, 10° C for 24 hours. Gels were then silver stained and analyzed with Scion Image to determine the proportions of fetal, neonatal/IIA/IIX, and slow myosin isoforms each sample expressed. The results indicate that litters exposed to bethamethasone expressed significantly higher concentrations of fetal myosin isoforms (34.21% +/- 2.57%) in all of the studied muscles, in comparison to control muscles (26.2% +/- 3.07%). Control litters also expressed overall significantly higher levels of neonatal/IIA/IIX myosin (56.61 +/- 2.4%) than seen in treated litters (52.46 +/- 2.28%). These results refute our hypothesis. The greater overall percentage of fetal myosin potentially indicates that the treated muscles would not exhibit adult physiological properties and suggests that hindlimb and ventilatory muscles exposed to betamethasone are not better prepared to sustain ventilation than control muscles.