Meeting Abstract
P1.42 Thursday, Jan. 3 Development of the guinea pig (Cavia porcellus) rectus abdominus muscle: effects of prenatal steroids GORDON, V.K.**; THOMPSON, K.E.; WEIGAND, K.L.; DEAROLF, J.L.; Hendrix College, Conway, AR; Hendrix College, Conway, AR; Hendrix College, Conway, AR; Hendrix College, Conway, AR gordonvk@hendrix.edu
The ability of a neonate to sustain life after birth is dependent on the body�s ability to adjust to the changes in environment from intra- to extra-uterine life. The changes created in major organs, such as the lungs, kidneys, and heart, are primarily facilitated through the production of a glucocorticoid surge 10-15 days before a term birth. With previous research in mind, it was hypothesized that glucocorticoid treatment in the fetal guinea pig causes atrophy of muscle fibers and a decrease in the percentage of the fast-twitch fibers in the rectus abdominus muscle. To test these hypotheses, we injected pregnant guinea pigs with either betamethasone (0.5 mg/kg) (treated) or sterile water (control) on days 43 and 44 (65% of gestation), 50 and 51 (75% of gestation), and 57 and 58 (85% of gestation) before collecting muscle samples. We then used a myosin ATPase assay and antibody staining to determine the percentage of each type of fiber (fast-twitch and slow-twitch) present in the treated and control rectus abdominus samples. Diameters of the fast- and slow-twitch fibers were also measured. The data collected did not show a decrease in the percentage of fast-twitch fibers (control: 89.3% ± 0.7%; treated: 88.6% ± 0.6%) or a decrease in the diameters of the fast- (control: 15.80 ± 2.34 µm; treated: 13.71 ± 1.84 µm) or slow-twitch (control: 16.37 ± 2.34 µm; treated: 14.16 ± 1.50 µm) fibers. However, the injection protocol currently in use is based on a single fetus in each litter, and guinea pigs generally have between one and eight fetuses per litter. Thus, research on the expression of lung surfactant proteins is being conducted to determine if each fetus in the treated litters is receiving the correct steroid dosage.
