Regulatory response to washout of amniotic fluid in sheep

Yang, Qin; Davis, Lowell E.; Hohimer, A. Roger; Faber, J. Job; Anderson, Debra F.

doi:10.1152/ajpheart.00740.2004

Cited by 12 publications

(19 citation statements)

References 20 publications

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“…The present study also suggests that the increase in intramembranous absorption rate during intra-amniotic infusion is not due to changes in amniotic fluid and/or fetal blood concentrations of the major solutes, consistent with previous studies (1,9,18). This conclusion is based on the observations that the intramembranous concentration differences for potassium, sodium, calcium, chloride, and glucose were unchanged during the infusions.…”

Section: Discussionsupporting

confidence: 92%

“…In those experiments, lactated Ringer solution was continuously infused into the amniotic compartment at 3 l/day for 3 days, while amniotic fluid was withdrawn at the same rate and discarded. Amniotic fluid volume nearly doubled during washout, suggesting the presence of chemical regulators in amniotic fluid that function to modulate intramembranous absorption (18). Further, the change in amniotic fluid volume during the washout differed between intact fetuses and those with a trachealesophageal shunt, suggesting either a pulmonary source or removal by swallowing of amniotic fluid regulatory factors of intramembranous absorption that are present in amniotic fluid.…”

mentioning

confidence: 98%

“…However, membrane stretch has been shown to have no effect on amniotic fluid volume in late-gestation sheep (7). The presence of stimulators and/or inhibitors of intramembranous absorption in amniotic fluid was demonstrated in amniotic fluid washout studies (1,18). In those experiments, lactated Ringer solution was continuously infused into the amniotic compartment at 3 l/day for 3 days, while amniotic fluid was withdrawn at the same rate and discarded.…”

mentioning

confidence: 99%

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Inhibitor of intramembranous absorption in ovine amniotic fluid

Brace

Cheung

Anderson

2014

American Journal of Physiology-Regulatory, Integrative and Comp

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Intramembranous absorption increases during intra-amniotic infusion of physiological saline solutions. The increase may be due partly to the concomitant elevation in fetal urine production as fetal urine contains a stimulator of intramembranous absorption. In this study, we hypothesized that the increase in intramembranous absorption during intra-amniotic infusion is due, in part, to dilution of a nonrenal inhibitor of intramembranous absorption that is present in amniotic fluid. In late-gestation fetal sheep, amniotic fluid volume and the four primary amniotic inflows and outflows were determined over 2-day intervals under three conditions: 1) control conditions when fetal urine entered the amniotic sac, 2) during intra-amniotic infusion of 2 l/day of lactated Ringer solution when urine entered the amniotic sac, and 3) during the same intra-amniotic infusion when fetal urine was continuously replaced with lactated Ringer solution. Amniotic fluid volume, fetal urine production, swallowed volume, and intramembranous absorption rate increased during the infusions independent of fetal urine entry into the amniotic sac or its replacement. Lung liquid secretion rate was unchanged during infusion. Because fetal membrane stretch has been shown not to be involved and because urine replacement did not alter the response, we conclude that the increase in intramembranous absorption that occurs during intra-amniotic infusions is due primarily to dilution of a nonrenal inhibitor of intramembranous absorption that is normally present in amniotic fluid. This result combined with our previous study suggests that a nonrenal inhibitor(s) together with a renal stimulator(s) interact to regulate intramembranous absorption rate and, hence, amniotic fluid volume. amniotic fluid volume regulation; fetal swallowing; fetal urine production; lung liquid secretion; intramembranous absorption OUR UNDERSTANDING OF THE REGULATION of amniotic fluid volume has been continually evolving. Current concepts are that, in late gestation, amniotic fluid volume is dependent on a balance between two primary amniotic inflows (fetal urine and lung liquid) and two primary outflows (swallowing and intramembranous absorption). Although fetal urine production, lung liquid secretion, and swallowing have been shown to be regulated by the fetal nervous and endocrine systems, the regulation of intramembranous absorption rate is less well understood.Conceptually, intramembranous absorption may be regulated by chemical substances present in amniotic fluid and/or stretch of the fetal membranes. However, membrane stretch has been shown to have no effect on amniotic fluid volume in late-gestation sheep (7). The presence of stimulators and/or inhibitors of intramembranous absorption in amniotic fluid was demonstrated in amniotic fluid washout studies (1, 18). In those experiments, lactated Ringer solution was continuously infused into the amniotic compartment at 3 l/day for 3 days, while amniotic fluid was withdrawn at the same rate and discarded. Amniotic fluid volume...

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Section: Discussionsupporting

confidence: 92%

mentioning

confidence: 98%

mentioning

confidence: 99%

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Inhibitor of intramembranous absorption in ovine amniotic fluid

Brace

Cheung

Anderson

2014

American Journal of Physiology-Regulatory, Integrative and Comp

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“…It should be noted that a mechanical stimulus would cause the regulation of total intrauterine volume, including the fetus, whereas a chemical stimulus would regulate amniotic fluid volume per se, a vital distinction. Previous experiments performed in our laboratory (21) support the existence of a biochemical process because isovolumic replacement of amniotic fluid with artificial fluid caused an increase in amniotic fluid volume. However, a biochemically mediated control does not preclude the concurrent operation of a mechanical process.…”

Section: Discussionmentioning

confidence: 55%

Function curve of the membranes that regulate amniotic fluid volume in sheep

Faber

Anderson

Hohimer

et al. 2005

American Journal of Physiology-Heart and Circulatory Physiology

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-Seven singleton 120-day fetal lambs were prepared with a shunt from the lung to the gastric end of the esophagus, a bladder catheter, and multiple amniotic fluid and vascular catheters. The urachus was ligated. Beginning 7 days later, amniotic fluid volumes were determined by drainage, followed by replacement with 1 liter of lactated Ringer (LR) solution. Urine flow into the amnion was measured continuously. In 14 of 27 experiments, amniotic fluid volumes were determined again 2 days after the inflow into the amnion had consisted of urine only and in 13 experiments after the inflow of urine had been supplemented by an intraamniotic infusion of LR solution. Intramembranous absorption was calculated from the inflows and the changes in volume between the beginning and end of each experiment. The relations between absorption rate and amniotic fluid volume, the "function curves," were highly individual. Urine production during the infusion of LR solution did not decrease, fetal plasma renin activity decreased (P Ͻ 0.001), and amniotic fluid volume increased by 140% [SE (27%), P Ͻ 0.005], but the increase in the amniochorionic absorption rate of 411% [SE (48%), P Ͻ 0.001] was greater (P Ͻ 0.005) than the increase in volume. Each of the seven fetuses was proven capable of an average intramembranous absorption rate that exceeded 4.5 liters of amniotic fluid per day. During the infusion of LR solution, the increase in the rate of absorption matched the rate of infusion (both in ml/h), with a regression coefficient of 0.75 (P Ͻ 0.001). Thus, even for large amniotic fluid volumes, volume is not limited by the absorptive capacity of the amniochorion, and, at least in these preparations, the position of the function curve and not the natural rate of inflow was the major determinant of resting amniotic fluid volume. fetus; polyhydramnios; amniochorion; intramembranous absorption DURING THE LAST 50 DAYS of the 150-day gestation period of fetal sheep, the production rate of amniotic fluid is on the order of 500 ml/day (6, 19). Under steady-state conditions, the rate of absorption will be the same. Because the volume of amniotic fluid is relatively constant over this period of time, it follows that this volume is almost perfectly controlled.Production of amniotic fluid results from fetal urination and lung fluid secretion (5, 13, 16). There is good evidence that urine production and lung fluid flow do not serve to regulate amniotic fluid volume because neither lung fluid flow nor urine production properly respond to induced changes in volume (9, 11). Thus, although substances secreted in these fluids may affect volume regulation (14), whatever regulatory mechanism exists must modulate the rate of fluid elimination to adapt to changes in fluid production. Fluid elimination consists of swallowing by the fetus and of absorption of fluid by the amniochorion, the membrane that surrounds the amniotic cavity. Amniochorionic absorption of amniotic fluid ["intramembranous absorption" (7, 14)] proceeds by means of an as-yetunresolved mec...

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“…The use of lactated Ringer solution had the advantage of minimizing the risk of infection and establishing a baseline amniotic fluid volume that was identical for all fetuses. This also allowed us to more easily compare the results from these experiments with our previously published experiments (18). The duration of the experiments was long enough to allow the establishment of a new steady state, making the initial composition of the replacement fluid of no great consequence.…”

Section: Methodsmentioning

confidence: 93%

Intramembranous absorption rate is unaffected by changes in amniotic fluid composition

Anderson¹,

Yang²,

Hohimer³

et al. 2005

American Journal of Physiology-Renal Physiology

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Experiments were performed to determine the effect of amniotic fluid dilution on the rate of intramembranous absorption. Seven fetal sheep at 118 days gestation were instrumented with a shunt between the trachea and esophagus and arterial and venous vascular catheters. In addition, the urachus of the fetal bladder was ligated, and a catheter was placed in the bladder. Ligation of the urachus does not interfere with urine flow into the amnion. After 5 days of recovery, fetuses were randomly assigned to one of two protocols; all fetuses completed both protocols. In the fetuses in the control period, continuous urine flow measurement was begun. In the fetuses assigned to the isovolumic dilution protocol, continuous urine flow measurement was also begun and, in addition, amniotic fluid was continually exchanged with lactated Ringer solution on an isovolumic basis. After 3-4 days, fetal blood pressures and amniotic fluid volumes were determined. Amniotic fluid volumes were determined by drainage. Each fetus was then assigned to the remaining protocol. The presence of the tracheal-esophageal shunt and the ligation of the urachus allowed the rate of intramembranous absorption to be calculated. Isovolumic exchange showed no effect on fetal vascular pressures, blood-gas values, or urine production. We could demonstrate no effect of isovolumic dilution of amniotic fluid on its volume. However, we were able to demonstrate an inverse relationship between amniotic fluid volume and intramembranous absorption (P Ͻ 0.02).fetal fluid balance THE RATE OF CHANGE IN VOLUME of amniotic fluid is determined by the difference between the inflow of fluid and the outflow of fluid into the amniotic space. The most significant sources of fluid are fetal urine and lung fluid secretions, whereas the loss of fluid occurs primarily through swallowing and intramembranous absorption (1)(2)(3)8). Intramembranous absorption refers to the movement of fluid from the amniotic fluid into the fetal blood perfusing the amnion and chorion (11) and ranges from ϳ250 to 500 ml/day (8). While intramembranous absorption rate will change in response to a variety of fetal perturbations including hypoxia (13, 16), esophageal ligation (9), and changes in the osmotic gradient between the fetal plasma and the amniotic fluid (7), the basis for any regulatory control over the intramembranous absorption rate is unknown.The present series of experiments was designed to test the hypothesis that the rate of intramembranous absorption is independent of the composition of the amniotic fluid. The contribution of intramembranous absorption was isolated by continually measuring urine flow and eliminating the contributions of lung fluid secretion and fetal swallowing through creation of a fistula between the esophagus and the trachea. Under these conditions, the composition of the amniotic fluid is dependent on the contribution of the urine flow and the contribution of diffusional exchange between the amniotic fluid and the fetal plasma. In an attempt to determine whether the ...

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Regulatory response to washout of amniotic fluid in sheep

Cited by 12 publications

References 20 publications

Inhibitor of intramembranous absorption in ovine amniotic fluid

Inhibitor of intramembranous absorption in ovine amniotic fluid

Function curve of the membranes that regulate amniotic fluid volume in sheep

Intramembranous absorption rate is unaffected by changes in amniotic fluid composition

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