P1.170 Wednesday, Jan. 4 The effect of prenatal steroids on the fast-twitch fibers of the fetal guinea pig scalenus BUTLER, M.R.**; CHUGHTAI, A.; WALKER, R.A.; DEAROLF, J.L.; Hendrix College, Conway, AR email@example.com
Glucocorticoids, like betamethasone and dexamethasone, are commonly used to prevent infant mortality in premature births. Injecting mothers with these steroids has been shown to greatly improve lung function in premature infants. However, their effects on ventilatory muscles are not very well documented. In this study, the effect of betamethasone on the size and proportions of fast-twitch types IIA and IIX fibers of the scalenus, an accessory ventilatory muscle used in labored breathing, of fetal guinea pigs will be determined. Based on a previous study of the rectus thoracis, another inspiratory muscle, we hypothesize that there will be an increase in the number of IIA fast-twitch fibers and the diameter of both IIA and IIX fibers will be larger in treated individuals. Pregnant guinea pigs were injected with either betamethasone or sterile water twice a week, twenty-four hours apart, at 65%, 75%, and 85% gestation. Muscle samples were collected and stained for their myosin ATPase activity, or with an antibody to slow myosin, to identify slow-twitch fibers. Additional samples were stained with 2F7 (antibody to IIA myosin) to identify IIA and IIX fibers. Digital images of the stained sections were taken and analyzed for 2F7 staining density and fiber diameter using Scion Image. If our hypothesis is supported, babies treated with prenatal steroids may have a less difficult time in labored breathing involving the scalenus than their untreated counterparts, due to the ability of the muscle to contract quicker and with more force.