Meeting Abstract

P2.139  Monday, Jan. 5  Prenatal steroids: altering myosin heavy chain isoform expression in guinea pig diaphragm WEIGAND, K.L.**; DEAROLF, J.L.; Hendrix College, Conway, AR weigand@hendrix.edu

Glucocorticoid steroids are given to women at risk for preterm delivery to induce rapid development of the lungs of their fetuses and decrease the risk of mortality. Because these steroids stimulate cellular differentiation, we hypothesize that fetal diaphragms exposed to a steroid (treated) will express less developmental (fetal) and more adult (fast: neonatal, IIa, IIx; slow: I) myosin heavy chain isoforms than control (sterile water) fetal muscles. To test these hypotheses, we investigated 2 protocols in guinea pigs. The short protocol called for 1 round (2 injections, 24 hours apart) of betamethasone (0.5 mg/kg maternal weight) injections, and the fetal diaphragm samples were collected at 70% gestation. The long protocol called for 3 rounds (1 round/week) of injections, and the samples were collected at 85% gestation. Diaphragm samples from both injection protocols were collected and extracted using a urea/thiourea sample buffer. SDS-polyacrylamide gel electrophoresis was used to separate and identify the myosin isoforms (fetal, neonatal/IIa/IIx and slow) present in these samples. Each gel was silver stained, dried, and scanned into digital format. Scion Imaging software was used to quantify the proportion of each isoform relative to the overall myosin content of the sample. There was no significant difference in the myosin expression of either control or treated fetal diaphragms in the short protocol. However, there was significantly more fetal myosin in the muscles of the treated fetuses ([T] 20.10 +/- 1.23%; [C] 12.73 +/- 2.12%) and less adult fast myosin ([T] 62.42 +/- 2.24%; [C] 67.12 +/- 1.46%) in the long protocol. Since fetal myosin has a slower contraction speed than adult proteins, the delay in development will reduce the ability of the diaphragm to respond to ventilatory challenges.