Meeting Abstract

P1.40  Thursday, Jan. 3  The effects of multiple courses of glucocorticoids on the fetal guinea pig (Cavia porcellus) scalenus muscle RHOADS, S.K.**; HERROLD, M.L.; HELLIE, A.C.; WEIGAND, K.L.; DEAROLF, J.L.; Hendrix College, Conway, AR rhoadssk@hendrix.edu

Synthetic glucocorticoids are administered to pregnant women in order to improve neonatal viability when preterm labor is a threat. However, some studies have shown that these steroids have detrimental effects on breathing and locomotor muscles. Therefore, it is hypothesized that the scalenus muscle, an accessory inspiratory muscle, of fetuses exposed to glucocorticoids will exhibit a decrease in the percentage of type II (fast-twitch) fibers and have smaller fiber diameters. To test these hypotheses, samples of the scalenus muscle were taken from guinea pig fetuses whose mothers were injected with betamethasone (0.5 mg/kg body weight) (treated) or sterile water (control) at 43 and 44 days (65%), 50 and 51 days (75%), and 57 and 58 days (85%) gestation. The percentage of fast-twitch fibers and the average diameters of fast- and slow-twitch fibers were measured in each group. The results of the experiment revealed that fetal exposure to glucocorticoids does not affect either the fiber-type profile or fiber diameters of the scalenus. The average percentage of fast-twitch fibers of treated litters (93.2% ± 0.5) was almost identical to that of control litters (93.9% ± 0.3). The average diameters of the fast-twitch (control: 13.01 ± 0.79 µm; treated: 12.09 ± 0.51 µm) and slow-twitch (15.63 ± 0.86 µm; 14.98 ± 0.66 µm) fibers also did not significantly deviate from each other. Our results suggest that fetuses exposed to steroids will not be at higher risk for breathing problems because of slower contraction speeds or muscle weakness.