Meeting Abstract

P2.136  Monday, Jan. 5  Do prenatal steroids affect maternal breathing muscles? REIN, R.**; WEIGAND, K.L.; DEAROLF, J.L.; Hendrix College, Conway, AR reinrr@hendrix.edu

Prenatal steroids are administered to expecting mothers who begin to go into labor prematurely in order to quickly develop the lung tissue of their fetuses. Previous research has shown that exposure to these steroids has caused atrophy of adult muscles, including diaphragm. Thus, we hypothesize that exposure to prenatal steroids will cause atrophy of maternal muscle fibers, specifically in four breathing muscles: the diaphragm, scalenus, rectus thoracis, and rectus abdominus. Pregnant guinea pigs (Cavia porcellus) were injected twice weekly for three weeks with betamethasone (0.5 mg/kg body weight at 65%, 75%, and 85% gestation) or sterile water. Samples of all four muscles were collected from treated and control adults and prepared for histochemistry. Sample sections were cut in a cryostat and stained for myosin ATPase. The diameters of twenty-five fibers of each type (fast and slow twitch) were measured using Scion Image, and the data were compared across treatment groups. The fast twitch fibers in the treated scalenus (41.5 +/- 4.0 m) and rectus thoracis (45.5 +/- 3.8 m) were smaller than their respective controls (42.2+/- 3.8 m; 47.8 +/- 1.6 m). In addition, the slow twitch fibers in the treated rectus abdominus (53.5 +/- 2.8 m) were smaller than those in the control muscles (57.1 +/- 1.3 m). Thus, the effects of steroid exposure seem to be muscle and fiber type specific. However, no significant differences were found between the treated and control fiber diameters in all four muscles. These results demonstrate that exposure to a prenatal steroid caused no significant fiber atrophy in the four breathing muscles and suggest that the maternal muscles are receiving little to none of the steroid, which is all being delivered to the fetus as desired.