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 betamethasone alone, or in combination with thyroid hormone (thyroxine; T-4), on postnatal renal and endocrine adaptations in preterm newborn lambs. Ovine fetuses (126 d of gestation; term = 150 d) received single, ultrasound-guided intramuscular injections of saline, 0.5 mg/kg betamethasone (Celestone Soluspan(R)), or 0.5 mg/kg betamethasone plus 60 mu g/kg T-4. After 48 h, lambs were delivered, treated with surfactant (Survanta(R), 100 mg/kg), and ventilated for 3 h. Due to maintained urine flow 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. Although renal blood flow, renal plasma flow, and fractional sodium excretion rates did not differ, betamethasone versus saline values for the filtration fraction (11.9 +/- 1.5 versus 7.4 +/- 1.5%) and total sodium reabsorption (196 +/- 38 versus 81 +/- 16 mu Eq . min(-1). kg(-1)) were increased, Betamethasone versus saline treatment also was associated 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 treatment 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 and endocrine responses.