Changes in fetal renal function in response to infusions of a hyperosmotic solution of mannitol to the ewe.

Abstract

SUMMARY1. In six pregnant ewes a reduction in transplacental water transfer was produced by increasing maternal osmolality (by infusion of 180 g of mannitol in 500 ml of 0-15 M-sodium chloride) and the fetal renal responses to this reduction in water transfer were studied. These responses were compared with the renal responses of five other chronically catheterized fetal lambs whose mothers received I.v. infusions of 500 ml of 0-15 M-sodium chloride.2. Intravenous infusion of 500 ml of 0-15 M-sodium chloride to the ewe produced no changes in fetal plasma sodium, potassium or plasma renin activity and had no effect on fetal renal function.3. After i.v. infusion of mannitol to the ewe, fetal urinary flow rate fell from control levels of 0-69 + 0-12 ml/min to 0-32 + 0 04 ml/min (S.E. of mean, P < 0 006). This fall in urinary flow rate was due to increased water reabsorption because there was no change in glomerular filtration rate and osmolar clearance.4. Fetal urinary sodium excretion increased from 16-2 + 2-0 /imol/min, to 34-2 + 6-,9 ,mol/min (S.E. of mean, P < 0 04). This increase in fetal urinary sodium excretion was due to a fall in the fractional reabsorption of sodium which was related to the rise in fetal plasma sodium levels that occurred following infusion of mannitol to the ewe. The increases in fetal plasma sodium levels were also associated with reductions in fetal plasma renin activity.5. It is concluded that the fetal lamb is capable of limiting renal water excretion and modifying renal sodium excretion in order to maintain the volume and composition of its body fluids.

Effect of maternal hydration on the increase of amniotic fluid index

“…Water deprivation or mannitol infusion resulted in a decrease in fetal urine flow in ewes, implicating maternal osmolality as an important variable (9)(10)(11)13). However, it is also clear that changes in fetal volume or osmolality can alter fetal urine output, AF volume and fetal intravascular volume (10).…”

Salt intake and reproductive function in sheep

“…For example, fetal urine flow rate falls and urine osmolarity rises when the ewe is dehydrated or infused with hypertonic mannitol (Lumbers and Stevens, 1983). By contrast, the fetus appears to be protected from both a high maternal salt intake (0.17 M NaCl) and moderate salt depletion (Stevens and Lumbers, 1986).…”

A method for determining baroreflex‐mediated sympathetic and parasympathetic control of the heart in pregnant and non‐pregnant sheep

“…Catheters were placed in the trachea for monitoring respiration, in a femoral artery for measurement of blood pressure and in both femoral veins for sampling of blood and infusion of drugs. In pregnant ewes fetuses were also cannulated using methods described previously (Lumbers & Stevens, 1983). Procaine penicillin (600 mg) and dihydrostreptomycin sulphate (750 mg) were given i.m.…”