P1.169 Wednesday, Jan. 4 The effect of prenatal steroids on the fatigue resistance of the fetal guinea pig diaphragm RILEY, L.A.**; SCIORTINO, A.; WALKER, R.A.; DEAROLF, J.L.; Hendrix College, Conway, AR email@example.com
Glucocorticoids are administered to mothers at risk of preterm birth to accelerate fetal lung maturation. Though the application of these steroids has increased viability in premature births, little is known about the effects of glucocorticoids on the development of breathing muscles. Studies in our lab have shown that exposure to prenatal steroids results in an increase in the oxidative capacity of breathing muscles. Also, a positive correlation exists between oxidative capacity and fatigue resistance in the adult diaphragm. Thus, an increase in oxidative capacity in steroid-treated fetal muscles may lead to an increase in fatigue resistance. We hypothesize that the administration of betamethasone during muscle fiber differentiation will increase the fatigue resistance of the diaphragm in fetal guinea pigs. To test this hypothesis, we removed the diaphragm from fetal guinea pigs that were treated with two injections per week of betamethasone or sterile water (control). These injections occurred twenty-four hours apart at 65%, 75%, and 85% gestation. We then measured the contractile abilities of these muscles using a standard two-minute fatigue test. Results that support our hypothesis would indicate that a multi-course exposure to betamethasone leads to a more developed, fatigue-resistant diaphragm. Therefore, premature infants given this treatment may be better able to sustain ventilation during times of stress than untreated infants.