Meeting Abstract

P2.162  Saturday, Jan. 5  Effects of prenatal steroids on the citrate synthase activity of the fetal guinea pig (Cavia porcellus) diaphragm MCGRAIL, K.A.*; WALKER, R.A.; DEAROLF, J.L.; RICHMOND, J.P.; Hendrix College, Conway, AR; Univ. of North Florida, Jacksonville, FL mcgrailka@hendrix.edu

Glucocorticoids are often given to women in clinical settings who are expected to go into preterm labor. These corticosteroids ensure that the lungs of premature fetuses mature before birth, thereby increasing the chances of survival for these preterm infants. However, the effects of these steroids on the development of ventilatory muscles are not well known. Studies in our laboratory have shown that multi-course prenatal treatment with corticosteroids increases the proportions of highly oxidative fibers in fetal guinea pig breathing muscles. These findings suggest that prenatal glucocorticoids accelerate muscle development. Based on the previous results, we hypothesize that the diaphragm muscles of fetal guinea pigs treated with the steroid will show increased citrate synthase (CS) enzyme activity, an important enzyme for aerobic respiration, than those not treated with the steroid. To test this hypothesis, pregnant guinea pigs were injected with betamethasone (0.5 mg/kg) or sterile water twice a week, 24-hours apart, for three weeks at 65%, 75%, and 85% gestation. Samples of the diaphragms were then prepared, and their CS activities were measured with a microplate reader under the following conditions: 50 mM imidazole, 0.25 mM DNTB, 0.4 mM acetyl CoA, and 0.5 mM oxaloacetate, pH 7.5 at 37°C. The rate of change of the assay absorbance (at 412 nm) at the maximum linear slope (Vmax) was used to calculate the CS activities of the control and treated fetal diaphragms, and the average activities of the muscles were compared. If our hypothesis is supported, prenatal steroids could prepare premature babies for ventilation by increasing fatigue resistance in the diaphragm.