SINGLE-DOSE FETAL BETAMETHASONE ADMINISTRATION STABILIZES POSTNATAL GLOMERULAR-FILTRATION RATE AND ALTERS ENDOCRINE FUNCTION IN PREMATURE LAMBS

These studies determined the effects of fetal treatment with betametha sone alone, or in combination with thyroid hormone (thyroxine; T-4), o n postnatal renal and endocrine adaptations in preterm newborn lambs. Ovine fetuses (126 d of gestation; term = 150 d) received single, ultr asound-guided intramuscular injections of saline, 0.5 mg/kg betamethas one (Celestone Soluspan(R)), or 0.5 mg/kg betamethasone plus 60 mu g/k g T-4. After 48 h, lambs were delivered, treated with surfactant (Surv anta(R), 100 mg/kg), and ventilated for 3 h. Due to maintained urine f low in the betamethasone-treated animals and a significant decrease in the saline group, betamethasone versus saline urine flow values (0.11 +/- 0.03 versus 0.03 +/- 0.004 ml min(-1) kg(-1)) were significantly elevated by the end of studies. GFR (1.5 +/- 0.3 versus 0.8 +/- 0.2 mL . min(-1). kg(-1)) and mean blood pressure (61 +/- 4 versus 42 +/- 3 mm Hg) values also were higher in the betamethasone-treated animals. A lthough renal blood flow, renal plasma flow, and fractional sodium exc retion rates did not differ, betamethasone versus saline values for th e filtration fraction (11.9 +/- 1.5 versus 7.4 +/- 1.5%) and total sod ium reabsorption (196 +/- 38 versus 81 +/- 16 mu Eq . min(-1). kg(-1)) were increased, Betamethasone versus saline treatment also was associ ated with significant reductions in plasma angiotensin II (125 +/- 23 versus 550 +/- 140 pg/mL) and AVP (116 +/- 19 versus 230 +/- 77 pg/mL) levels. Overall, the effects of combined betamethasone + T-4 treatmen t were similar to the effects of betamethasone alone. Conclusions: 1) fetal betamethasone injection 48 h before delivery stabilizes CFR and significantly alters endocrine function in preterm newborn lambs, and 2) the addition of T-4 does not augment betamethasone-induced renal an d endocrine responses.