Meeting Abstract

P2.166  Saturday, Jan. 5  The effect of betamethasone on the citrate synthase activity in fetal guinea pig rectus abdominus KOMPELLI, A.R.*; DEAROLF, J.L.; RICHMOND, J.P.; Hendrix College, Conway, AR; Univ. of North Florida, Jacksonville, FL kompelliar@hendrix.edu

Currently, glucocorticoids are used to promote the survival of premature infants by accelerating their lung development. However, very little is known presently about how these steroids affect breathing muscle development. Work in our laboratory has shown that one of these steroids, betamethasone, increases the concentration of NADH, an oxidative enzyme, in the scalenus, an accessory inspiratory muscle in fetal guinea pigs. These results suggest prenatal glucocorticoids accelerate the acquisition of mitochondria by fetal muscle. Thus, we propose that glucocorticoids will increase the activity of citrate synthase (CS), a mitochondrial oxidative enzyme, in the rectus abdominis (RA), an expiratory muscle of guinea pigs. This hypothesis was tested by quantifying CS activity in RA muscles of steroid-treated and control fetal guinea pigs. Pregnant guinea pigs were given 2 injections, 24-hours apart, of betamethasone (0.5 mg/kg) or sterile water (control) at 65%, 75% and 85% gestation. Twenty-four hours after the last injection, females were euthanized and fetal RA was collected and homogenized. Kinetic assays were performed, and the CS enzyme activities (µmol/min*g) of the fetal muscles were calculated from the rate of change of the absorbance at the maximum linear slope. To determine whether CS activity is higher in treated muscles, an ANOVA was used to compare the average CS activities between treated and control muscles. If the activity of CS is higher in the treated muscles, they may be better able to resist fatigue in comparison to control muscles. Thus, neonates exposed to prenatal steroids will be better able to respond to ventilatory challenges.