Meeting Abstract

P1.35  Monday, Jan. 4  Effects of betamethasone on the external abdominal oblique of prenatal Cavia porcellus WHARTON, W.L.**; MARSHALL, S.L.; PREHODA-WYERS, M.M.; DEAROLF, J.L.; Hendrix College, Conway Arkansas Lewis.wharton@gmail.com

When a fetus is anticipated to be born prematurely, its mother is administered glucocortocoids, notably betamethasone, because this steroid is known to encourage differentiation of lung tissue. The study we conducted examined the effects of these steroids on auxiliary breathing muscle tissue differentiation in prenatal guinea pigs. Previous studies have shown that these steroids encourage muscle fiber type differentiation in non-ventilatory muscles. Thus, we hypothesize that the steroid-treated ventilatory muscle tissue, specifically the external abdominal oblique (EAO), will contain higher numbers of IIA fast-twitch fibers than control muscles. Pregnant guinea pigs were injected with betamethasone (0.5 mg/kg), or sterile water for control group, on days 43, 44, 50, 51, 57, and 58 of gestation, and euthanized at day 59. The fetuses were then dissected, and EAO samples were collected. Sections of the fetal EAO samples were stained using immunohistochemistry with the differential antibodies A4591 (Blau) for slow twitch muscle fibers and 2F7 (Lucas) for IIA fast twitch muscle fibers. Images of the stained tissue were taken using a digital image analyses system and analyzed for the staining density of the fibers with Scion Image to classify the fast-twitch fibers as 2F7+ or 2F7-. Percentages of the 2F7+ fibers will be compared between treatment groups. Thus, the functional consequences of steroid treatment for the ventilatory muscle is development of more IIA fibers, which creates an improved capacity for slow contractions for extended periods of time, but decreases capacity of the muscle to respond to environmental stimuli necessitating accelerated ventilation.