ROLE OF FETAL SAC FLUIDS DURING MATERNAL WATER-DEPRIVATION IN SHEEP

Our aim was to determine the importance of amniotic and allantoic flui ds for the maintenance of fetal plasma composition during maternal deh ydration when water transfer from mother to fetus is likely to be redu ced. Eight pregnant ewes were studied before, during and after water d eprivation (36 h), firstly with the fetal fluid sacs intact and then w ith them drained of fluid for 5 days. When water deprivation was combi ned with drainage, the increases in the osmolalities, [Na+] and [CI-] in maternal plasma, in fetal plasma and in lung liquid; the increases in fetal urinary osmolality and [Na+]; and the increases in maternal p lasma and fetal plasma arginine vasopressin concentrations were greate r than those resulting from water deprivation alone. Our results show that during maternal water deprivation, an absence of fluid in the fet al sacs increases both the osmotic stimulus to the fetus and the fetal responses resulting in conservation of water and salt. We conclude th at, when the mother is deprived of water, fluid in the fetal sacs is u sed to limit the degree of maternal and fetal dehydration.