A COMPARATIVE-STUDY OF CARDIOVASCULAR, ENDOCRINE AND BEHAVIORAL-EFFECTS OF BETAMETHASONE AND DEXAMETHASONE ADMINISTRATION TO FETAL SHEEP

1. Chronically instrumented, late-gestation fetal sheep were prepared to: (1) characterize cardiovascular, endocrine and behavioural effects of fetal treatment with clinical doses of betamethasone and dexametha sone; (2) define specific differences, if any, in the actions of betam ethasone and dexamethasone of measured fetal responses; and (3) assess the contribution of changes in peripheral vascular resistance to the glucocorticoid-induced hypertension 2. Following baseline, either sali ne (n = 9), betamethasone (n = 9), or dexamethasone (n = 6) was infuse d for 48 h in fetal sheep commencing at 125 days of gestation. A prono unced increase in fetal blood pressure occurred following both betamet hasone and dexamethasone treatment. The nature and magnitude of this i ncrease was similar following treatment with either glucocorticoid. 3. To address possible mechanisms contributing to the glucocorticoid-ind uced fetal hypertension, fetal plasma catecholamine levels and changes in fetal femoral haemodynamics were assessed following fetal glucocor ticoid treatment. A fall in fetal plasma noradrenaline and adrenaline concentrations occurred during betamethasone and dexamethasone treatme nt. In contrast, a progressive femoral vasoconstriction occurred durin g betamethasone treatment. 4. A modest fall in the incidence of fetal breathing movements occurred during fet al treatment with either betam ethasone or dexamethasone. The magnitude of this reduction was similar with treatment of either glucocorticoid. The fall in fetal breathing during betamethasone and dexamethasone treatment was not associated wi th a fall in the incidence of fetal low voltage electrocortical activi ty. 5. Our results indicate that prenatal betamethasone and dexamethas one treatment of late-gestation fetal sheep, in doses similar to those employed clinically, is associated with fetal cardiovascular, endocri ne and behavioural effects. Both betamethasone and dexamethasone induc e similar increases in fetal blood pressure and similar falls in the i ncidence of fetal breathing movements. The pronounced betamethasone-in duced fetal hypertension is associated with an increase in fetal femor al vascular resistance.