Meeting Abstract
P2.138 Monday, Jan. 5 Does myosin heavy chain expression in intercostal muscles of Cavia porcellus vary with exposure to betamethasone? TOTTEN, D.C.**; WEIGAND, K.L.; DEAROLF, J.L.; Hendrix College, Conway, AR tottendc@hendrix.edu
Premature infants are at a higher risk of complications due to a lack of development of the organs associated with ventilation and gas exchange, so glucocorticoids, like betamethasone, are used in the medical community to accelerate the development of the lungs. However, the effects of these steroids on breathing muscle development are currently unknown. Since these steroids are known to stimulate differentiation, we hypothesize that treated muscles will express more adult fast (neonatal, IIa, IIx) myosin heavy chain (MHC) isoforms than control groups. To test this hypothesis, pregnant guinea pigs underwent two steroid injection protocols. In the short protocol, females had two injections at 70% gestation 24-hours apart, while the long protocol had females injected at 65%, 75%, and 85% gestation, two injections per week, 24-hours apart. Intercostal muscle samples were collected from all fetuses and extracted with an urea/thiourea buffer. Extractions were separated in SDS-polyacrylamide (7%) gels run at 275 V and 8°C for 24-hours. After being silver stained and dried, the gels where analyzed with Scion Image to determine the average proportions of fetal, neonatal/IIa/IIx, and slow MHC isoforms relative to the total myosin present. In the short protocol, treated muscles expressed significantly less fetal (46.1+/-2.5%) and more adult fast (36.2+/-2.2%) than controls (49.7+/-0.7%; 30.3+/-1.3%). In comparison, the treated muscles in the long protocol expressed significantly more fetal (27.7+/-1.9%) and less adult fast (46.8+/-3.8%) than controls (22.8+/-2.9%; 58.2+/-4.2%). The results from the short protocol support our hypothesis that betamethasone accelerates muscle development, which suggests that the intercostals of treated neonates will be better prepared for function at birth.
