Meeting Abstract

P2.163  Saturday, Jan. 5  The effect of prenatal steroids on the fatigue resistance of the fetal guinea pig diaphragm RILEY, L.A.*; WALKER, R.A.; DEAROLF, J.L.; Hendrix College, Conway, AR rileyla@hendrix.edu

The application of glucocorticoid steroids to women at risk of premature birth has increased the viability of their infants, but little is known about the effects of these steroids on the development of breathing muscles. We hypothesize that the administration of betamethasone, a glucocorticoid, during muscle fiber differentiation will increase the fatigue resistance of the diaphragm in fetal guinea pigs. To test this hypothesis, we removed diaphragms from fetal guinea pigs that were treated with two injections per week of betamethasone (0.5 mg/kg) or sterile water. These injections occurred twenty-four hours apart at 65%, 75%, and 85% gestation. We then measured the contractile abilities of the fetal diaphragms using a standard two-minute fatigue test and a tetanic force fatigue test. Results from the two-minute fatigue test demonstrated that exposure to prenatal steroids does not lead to a significant difference between the fatigue resistance of control and treated fetal diaphragms, while preliminary tetanic fatigue data showed that control diaphragms are slightly more fatigue resistant than treated diaphragms. However, when analyzing the contractile response of the diaphragm, we realized that no diaphragm (treated or control) reached tetanus during the standard two-minute fatigue test, which led to changes in our fatigue test protocol: the duration of the stimulation trains was extended and the time between trains was reduced. Using the revised fatigue test, results that support our hypothesis would indicate that a multi-course exposure to betamethasone leads to a more fatigue-resistant diaphragm. Therefore, treated premature infants may better sustain ventilation during times of stress than untreated infants.