Role of fetal sac fluids during maternal water deprivation in sheep

Abstract

SUMMARYOur aim was to determine the importance of amniotic and allantoic fluids for the maintenance of fetal plasma composition during maternal dehydration when water transfer from mother to fetus is likely to be reduced. Eight pregnant ewes were studied before, during and after water deprivation (36 h), firstly with the fetal fluid sacs intact and then with them drained of fluid for 5 days. When water deprivation was combined with drainage, the increases in the osmolalities, [Na+] and [Cl-] in maternal plasma, in fetal plasma and in lung liquid; the increases in fetal urinary osmolality and [Na+]; and the increases in maternal plasma and fetal plasma arginine vasopressin concentrations were greater than those resulting from water deprivation alone. Our results show that during maternal water deprivation, an absence of fluid in the fetal sacs increases both the osmotic stimulus to the fetus and the fetal responses resulting in conservation of water and salt. We conclude that, when the mother is deprived of water, fluid in the fetal sacs is used to limit the degree of maternal and fetal dehydration.

Fetal and maternal fluid balance in sheep during hyperthermia with and without water deprivation

“…The inhibitory effects of maternal heating and maternal water deprivation on fetal lung liquid production were additive, rather than synergistic. We have previously suggested that the increase in fetal plasma osmolality may be partly responsible for the decline in lung liquid production with maternal water deprivation (Dickson & Harding, 1994). We have shown that the effects of maternal heating and water deprivation on fetal urinary osmolality, but not the decrease in urine production, were synergistic rather than additive.…”

“…Daily rates of Na+, K+ and Cl-excretion in fetal urine and secretion in lung liquid have been adjusted for fetal body weight (Dickson & Harding, 1994).…”

“…Maternal water intake and urine output Rates of maternal water intake and urine output (collected in a bucket beneath the cage) were measured during and after each study period, and values were adjusted for maternal body weight (Dickson & Harding, 1994).…”

“…Production rates were measured by draining the fetal lungs and bladder for 6-8 h (Stevens & Lumbers, 1985;Dickson & Harding, 1987. Daily rates of Na+, K+ and Clexcretion in fetal urine and secretion in lung liquid have been adjusted for fetal body weight (Dickson & Harding, 1994).…”