EFFECT OF MATERNAL GLUCOCORTICOID TREATMENT ON FETAL FLUIDS IN SHEEP AT 0.4 GESTATION

Treatment of nine pregnant Merino ewes (64.0 +/- 0.4 days of gestation ) with dexamethasone (D; 0.76 mg/h for 48 h) resulted in significant a lterations in fetal fluids compared with eight saline-infused control animals (S; 63.0 +/- 0.9 days). There was a substantial increase in al lantoic fluid volume (177 +/- 18 ml, D vs. 31 +/- 6, S) but no change in amniotic fluid volume (248 +/- 12 ml, D; 305 +/- 24, S). For allant oic fluid there was a significant decrease in osmolality (213 +/- 4 mo smol/kg water, D; 230 +/- 5, S) and alterations in composition. Amniot ic fluid osmolality was unchanged (292 +/- 2 mosmol/kg water, D; 293 /- 1, S), but amniotic fluid composition was affected. In four fetuses in which bladder and amniotic cannulas were inserted at gestational a ge 68-75 days, fetal urine flow rate increased from a mean of 4.1 +/- 1.1 to 13.8 +/- 2.6 ml/h after 24 h and 11.8 +/- 3.0 ml/h at 48 h for a similar maternal D infusion, whereas no such increase occurred in fo ur control fetuses. All the fetal urine voided during a 3.5- to 4-h in fusion of Cr-51-labeled EDTA into the fetal bladder was directed to th e allantois. The results suggest that the increase in allantoic fluid volume resulted from increased fetal urine output into the allantoic c ompartment, although the composition of the excess allantoic fluid dif fered substantially from that of fetal urine. There was a greater inci dence of abnormal cotyledons in the D-infused ewes. Altogether the fin dings suggest that if maternal glucocorticoids are increased by some s tress early in pregnancy, there will be marked abnormalities in placen tal structure and in fetal fluids.