Biomedical subjects

Robert A Brace

Publications and source records attributed to Robert A Brace.

15 recordsLinked to original sources

PubMed2006

Sources of amniotic fluid erythropoietin during normoxia and hypoxia in fetal sheep.

OBJECTIVE: Erythropoietin is present in human amniotic fluid and has been suggested as a marker of fetal hypoxia. The objectives of the present study were to determine whether erythropoietin is present in ovine amniotic fluid, fetal urine, and/or lung liquid and whether concentrations in these compartments change in parallel with endogenous fetal plasma erythropoietin concentration when the latter is increased experimentally. STUDY DESIGN: In late gestation chronically catheterized fetal sheep, samples of amniotic fluid and plasma, urine and plasma, lung liquid, amniotic fluid, and plasma were collected before and up to 7 days after induction of 4 types of fetal hypoxia: (1) acute anemic hypoxia that was induced by a single fetal hemorrhage, (2) progressive anemic hypoxia that was induced by daily exchange transfusion, (3) acute hypoxic hypoxia that was induced by the reduction of maternal inspired oxygen content, or (4) chronic placental insufficiency that was induced by daily umbilicoplacental embolization for 4 days. Erythropoietin concentrations were determined by radioimmunoassay. Statistical testing included analysis of variance and least squares regression. RESULTS: Under basal, nonhypoxic conditions, amniotic fluid erythropoietin concentration averaged 33.2% +/- 1.6% (SE) of fetal plasma erythropoietin concentration, and basal fetal urine and lung liquid erythropoietin concentrations ranged from low (<10% of plasma concentration) to nondetectable. Unlike the strong correlation in humans, basal amniotic fluid and plasma erythropoietin concentrations were correlated only weakly (r = 0.259; r2 = 6.7%; P = .0027; n = 132). Amniotic fluid erythropoietin concentration approximately doubled after 12 hours of severe hypoxic hypoxia or after 24 hours of embolization-induced severe hypoxia but was unchanged after 12 hours of mild-moderate hypoxic hypoxia or 24 hours of anemic hypoxia. Concomitant fetal plasma erythropoietin concentrations increased to 28.1 +/- 5.3, 12.5 +/- 2.7, 10.8 +/- 4.6, and 10.0 +/- 1.3 times basal values, respectively. During progressive fetal anemia, urinary erythropoietin concentration increased almost 10-fold (P = .0023) but remained a small fraction (3.7% +/- 0.4%) of plasma concentration; at 12 hours of hypoxic hypoxia, lung liquid erythropoietin concentration did not vary with the severity of the hypoxia and remained low relative to plasma concentration (4.2% +/- 2.1%). CONCLUSION: Erythropoietin is present in ovine amniotic fluid, urine, and lung liquid. With only 3 potential sources, the fetal membranes appear to be the primary source of amniotic fluid erythropoietin in the nonhypoxic ovine fetus because basal urine and lung liquid erythropoietin concentrations are much lower than amniotic fluid concentrations. Although unchanged during mild-to-moderate fetal hypoxia, amniotic fluid erythropoietin concentration increases modestly during severe fetal hypoxia. In sheep, fetal urinary erythropoietin may contribute to this rise in amniotic fluid erythropoietin concentration during severe hypoxia, because fetal urinary and plasma concentrations increase in parallel during anemia.

Amniotic Fluid↗

PubMed2005

Comparison of amniotic and intramembranous unidirectional permeabilities in late-gestation sheep.

OBJECTIVE: Amniotic fluid volume is regulated by the intrinsic modulation of intramembranous absorption. However, neither the mechanisms nor the rate-limiting barriers of this transport are known. We tested the hypothesis that the amnion is the rate-limiting barrier of intramembranous absorption by comparing unidirectional permeabilities of the amnion in vitro and the intramembranous pathway in vivo. STUDY DESIGN: Unidirectional permeabilities to 99m technetium pertechnate or [14 C]inulin of fresh ovine amnion were measured in vitro in a Ussing chamber; the permeability-surface area products were calculated by the multiplication of the permeabilities by gestational age-specific amniotic surface areas. Unidirectional permeabilities of the intramembranous pathway of the 2 tracers were calculated from solute fluxes between amniotic fluid and fetal blood in chronically catheterized late-gestation fetal sheep. Statistical comparisons included t -tests, least squares regression, analysis of variance, and analysis of covariance. RESULTS: In the isolated amnion in vitro, the ratio of permeabilities in the amniotic fluid to chorionic direction and the reverse direction was not significantly different from unity for 99m technetium pertechnate (1.03+/-0.10 [SE]; n=7) or [14 C]inulin (1.10+/-0.17; n=7). In contrast, in the in vivo preparation, the ratio of intramembranous permeabilities outward from the amniotic fluid and the reverse direction was greater than unity for 99m technetium pertechnate (2.10+/-0.34; n=8; P=.014) and [14 C]inulin (4.68+/-1.24; n=7; P=.025). The permeability-surface area product of 99m technetium pertechnate (2.18+/-0.79 mL/min) of the isolated amnion was similar to the in vivo intramembranous permeability (n=8) in the amniotic fluid to fetal blood direction (1.42+/-0.34 mL/min) and greater than that in the reverse direction (0.84+/-0.25 mL/min; P=.046). The permeability-surface area product of [14 C]inulin of the amnion (0.53+/-0.20 mL/min) was similar to intramembranous permeability (n=7) in the amniotic fluid to fetal blood (0.68+/-0.15 mL/min) direction and greater than that in the reverse direction (0.22+/-0.06 mL/min; P=.0097). CONCLUSION: Solute transport across the ovine amnion depends on solute size and appears to be limited only by the amnion's passive diffusional properties. In vivo intramembranous transport similarly depends on solute size but is not exclusively a passive diffusional process because it is primarily unidirectional outward from the amniotic fluid. Although it is a major barrier, the amnion is not the only barrier and does not appear to be responsible for the unidirectional nature of intramembranous absorption. Thus, unidirectionality appears to be imparted by nonpassive mechanisms in non-amnion tissues, which most likely includes vesicular transport within the endothelial cells of the intramembranous microvessels.

Absorption↗

PubMed2005

Pre-delivery changes in amniotic fluid volume and composition in sheep.

OBJECTIVE: To determine the changes in amniotic fluid (AF) volume and solute concentrations during the last 3 weeks of gestation in fetal sheep with a ligated urachus. METHODS: AF volume as well as solute concentrations of AF, fetal urine, fetal blood, and maternal blood were measured serially over the last 24 days of gestation in chronically catheterized fetal sheep. Statistical analyses included regression analysis and analysis of variance (ANOVA). RESULTS: Delivery occurred at 145.5 +/- 1.1 (SE) days (n = 11 animals). AF volume averaged 913 +/- 46 mL (n = 119 determinations total from 11 animals) and was unchanged with time when analyzed against either gestational age (P = .9) or time prior to delivery (P = .81). Amniotic osmolality, sodium, chloride, glucose, and calcium concentrations decreased as gestation progressed, while potassium and lactate concentrations increased. Only amniotic lactate underwent a pre-delivery increase in concentration. From multivariate regression, AF solute concentrations correlated positively with fetal blood and urine concentrations and negatively with gestational age. CONCLUSIONS: In fetal sheep with a ligated urachus, AF volume does not decrease prior to labor and delivery. This differs from the sharp pre-delivery decrease in AF volume that occurs in rats, mice, and pigs and is similar to the relatively constant AF volume in humans, baboons, and monkeys. Further, pre-delivery changes in AF lactate concentration may reflect the consequences of a low AF volume. Regression analysis suggests that fetal blood and urine independently contribute to AF solute concentrations and that gestational age-specific changes in intramembranous transport also may contribute.

Amniotic Fluid↗

PubMed2005

Amniotic fluid volume and composition in mouse pregnancy.

OBJECTIVE: The current study was undertaken to determine simultaneous changes in amniotic fluid (AF) volume and composition across gestation in the pregnant mouse. METHODS: Young adult mice (6 to 7 weeks old) of the CB6F1 strain were mated overnight. AF was collected on consecutive days from embryonic days 9.5 through 18.5 for measurements of volume and composition. Statistical analysis included one-factor analysis of variance (ANOVA). RESULTS: AF volume increased from 18 +/- 4 (SE) microL on day 9.5 to a maximum of 147 +/- 4 microL on days 15.5 to 16.5 and decreased sharply to 17 +/- 3 microL on day 18.5. AF osmolality was unchanged except for a rise prior to delivery on day 19.5 to 20.5. AF sodium, calcium, and glucose concentrations increased and subsequently decreased as gestation progressed. AF potassium, chloride, and lactate concentrations initially decreased and then increased across gestation. Prior to day 9.5 and after day 18.5, AF volume was too small for volume or compositional determinations. CONCLUSIONS: In the mouse, the rise in AF volume from mid gestation to a maximum late in gestation is similar to that in humans while the sharp fall prior to delivery is not. As observed in the fetal sheep, the changes in fluid volume are associated with AF osmolality and solute concentration changes that are correlated with advancing gestational age. These observations together with the feasibility of quantifying AF volume and composition in the mouse fetus demonstrate the possibility of using genetically altered mice as a model for future studies on the molecular mechanisms underlying the regulation of AF volume and composition.

Amniotic Fluid↗

PubMed2004

Regulation of amniotic fluid volume: intramembranous solute and volume fluxes in late gestation fetal sheep.

OBJECTIVE: Recent studies suggest that amniotic fluid volume is regulated by the rate of intramembranous absorption of amniotic fluid into fetal blood. The purpose of the present study was to determine the simultaneous intramembranous solute and water fluxes to gain insight into the intramembranous transport and amniotic fluid volume regulatory mechanisms. STUDY DESIGN: All major amniotic inflows and outflows, except intramembranous flow, were eliminated in 10 fetal sheep over 8 hours by occlusion of the fetal trachea and esophagus; the fetal urine was drained to the exterior. Amniotic fluid composition and volume were measured before and at the end of the 8 hours. Solute and volume fluxes through the intramembranous pathway were calculated from amniotic fluid concentration and volume changes. Statistical analyses included t-tests, linear regression, and analyses of variance. RESULTS: Amniotic fluid volume decreased by 128 +/- 24 (SE) mL over 8 hours (P < .001), which was correlated only marginally with the fetal to amniotic fluid osmotic gradient (r=0.59; P = .072). Amniotic fluid sodium, chloride, calcium, and bicarbonate concentrations increased (P < .0001), even though there were net outward fluxes of these solutes; these outward fluxes occurred against concentration gradients; and the clearances of these solutes were the same despite widely differing amniotic fluid concentrations and fetal blood to amniotic fluid concentration gradients. With the use of multivariate regression, intramembranous solute fluxes separated into 2 components, which were a primary outward flux that correlated with the volume flux and a minor inward component that correlated with the fetal plasma to amniotic fluid concentration gradient for sodium, chloride, calcium (P < .001), and bicarbonate (P < .02). The concentration-dependent fluxes averaged approximately one third of the bulk fluxes and were in the opposite direction. CONCLUSION: The poor correlation of amniotic fluid volume reduction with the fetal-to-amniotic fluid osmotic gradient shows that the primary mechanism that mediates intramembranous volume flow is not passive osmosis in the normal fetus under basal conditions. The strong correlations of solute fluxes simultaneously with volume flux and concentration gradients suggest that intramembranous solute fluxes are mediated by both bulk flow and passive diffusion. The small size of the passive component relative to the size of the bulk component suggests that intramembranous solute transfer is mediated primarily by bulk flow with a smaller and usually oppositely directed contribution by diffusion down concentration gradients. Bulk flow by vesicular transport is the only known physiologic transport mechanism that is compatible with these data, but it is not known whether this occurs in the amnion or intramembranous blood vessels or both.

Amniotic Fluid↗

PubMed2004

Amniotic fluid volume responses to amnio-infusion of amniotic fluid versus lactated Ringer's solution in fetal sheep.

OBJECTIVE: The present study tested the hypothesis that an intra-amniotic infusion of amniotic fluid (AF) would produce a more sustained increase in AF volume than an infusion of lactated Ringer's solution. METHODS: Five chronically catheterized, late-gestation fetal sheep were studied over two 5-day periods with AF volume measured daily. After baseline measurements on day 1, 1 L of either warmed, previously frozen AF or warmed lactated Ringer's solution was infused intra-amniotically over 60 minutes. Two days later, the other fluid was infused. During the second week, fluids were infused in the opposite order. Analysis of variance (ANOVA) was used for statistical testing. RESULTS: Following intra-amniotic infusion (n = 20) of 1007 +/- 7 (SE) mL of either AF or Ringer's solution, intra-amniotic retention of the infused fluid was only moderate after 1 day (37.2% +/- 7.9%, P <.001) and was not significantly different from zero after 2 days (16.5% +/- 9.5%, P =.1). There were no significant differences in AF volume following infusion of AF versus lactated Ringer's solution or the order in which they were infused. AF compositional changes were similar except that pH and bicarbonate concentration were reduced as expected immediately after lactated Ringer's solution with a return to normal values after 1 day. AF lactate increased after lactated Ringer's solution infusion, declining to baseline values after 2 days. Fetal urine flow rate increased by 75% +/- 24% at 1 day postinfusion and there was no difference between infusates. CONCLUSIONS: The expansion of AF volume over 2 days following amnio-infusion does not appear to depend on minor compositional differences or the presence of microconstituents such as hormones, cytokines, or growth factors that are normally present in AF.

Adsorption↗

PubMed2004

Morphologic alterations in ovine placenta and fetal liver following induced severe placental insufficiency.

OBJECTIVES: Umbilical-placental embolization with microspheres has been used as a model of placental insufficiency and intrauterine growth restriction (IUGR). However, the effects of embolization on placental structure and organ morphology of the resulting IUGR fetus are relatively unexplored. In this study using ovine fetuses, we determined the location and distribution of microspheres within the placenta and explored the extent of placental and fetal organ morphologic changes induced by placental embolization. We hypothesized that microspheres administered into the umbilical circulation over 4 days would cause placental damage without significant morphologic alterations in fetal kidney or liver. METHODS: Eleven pregnant sheep at 118 +/- 1 (SE) days' gestation were studied. In six fetuses, embolization was induced by injections of 15-microm diameter microspheres on 4 successive days into the fetal descending aorta proximal to the umbilical arteries. Five fetuses served as time controls. RESULTS: In embolized fetuses, microspheres were detected in the placenta embedded in the fetal cytotrophoblastic layer or maternal parenchyma adjacent to villous cytotrophoblasts. Fetal cytotrophoblasts appeared normal except for loss of distinct separation between fetal and maternal cell layers. Microspheres were also detected in the fetal membranes within capillaries. The body weights of embolized fetuses were lower than controls, as were the body weight-normalized liver but not kidney weights. In the liver of the embolized fetuses, the number of hematopoietic cell clusters was markedly reduced, whereas the fetal kidneys appeared normal. CONCLUSIONS: We conclude that after 4 days of umbilical-placental embolization, microspheres were concentrated at the fetal villi proximal to the apical maternal-fetal interface and in the fetal membranes. There were noticeable morphologic changes in the embolized placentas, with no apparent gross damage to the placenta. The reduction in fetal liver weight and liver extramedullary hematopoietic cell abundance associated with embolization may predispose the fetus to alterations in liver function that could persist after birth.

Animals↗

PubMed2003

Renal and placental secretion of erythropoietin during anemia or hypoxia in the ovine fetus.

OBJECTIVE: The source of the erythropoietin (EPO) that circulates in the fetus is unknown although it is known that EPO does not cross the placenta and that fetal kidneys, liver, and placenta express the EPO gene. This study tested to what extent in vivo EPO secretion by the fetal kidneys and placenta can be demonstrated under normoxic and hypoxic conditions. STUDY DESIGN: Renal arterial and venous EPO concentrations were determined in eight late-gestation chronically catheterized fetal sheep made progressively anemic by exchange transfusion with saline solution over 5 to 8 days. In a separate additional series of experiments, umbilical arterial and venous EPO concentrations were determined in nine normoxic fetuses and in nine fetuses subjected to 12 hours of hypoxia induced by lowering maternal-inspired oxygen content. Organ secretion rates were calculated as the product of plasma flow rate and the arteriovenous concentration differences. RESULTS: Renal vein plasma EPO concentration was higher than the arterial concentration in 36 of 40 paired samples (P<.0001) by 16.3%+/-2.7% (mean+/-SE). This difference was concentration independent over a range of 12 to 4100 mU/mL. Renal EPO secretion rates were variable and averaged 155+/-105 mU/min when hematocrit was 31.3%+/-1.6% (n=5) and 1124+/-300 mU/min post-exchange transfusion when hematocrit was 15.6%+/-0.8% (n=12). In contrast, umbilical venous and arterial EPO concentrations (range 9-35 mU/mL), although highly correlated (r=0.94), were not different during normoxia (Po(2)=21.6+/-0.5 mm Hg, n=9). Under hypoxic conditions (Po(2)=15.6+/-0.4 mm Hg, n=9), umbilical vein EPO concentration (range 151-1245 mU/mL) was higher than arterial concentration (range 140-951 mU/mL) in eight of nine paired samples by 13.6%+/-3.3% (P<.01). Under these conditions, estimated umbilical EPO secretion rate was 27,900+/-11,500 mU/min. CONCLUSION: Under nonanemic, normoxic basal conditions, the kidneys secreted EPO into the fetal circulation, whereas secretion by the placenta was not demonstrated. In the phlebotomy-induced fetal anemia experiments, the kidney demonstrated marked, progressive increases in the rate of EPO production. Similarly, in the fetal hypoxemia experiments, the placenta demonstrated progressive increases--albeit an order of magnitude greater than the kidneys--in EPO production rate. As an extension of these findings, we speculate that the hypoproliferative neonatal anemia that invariably occurs in the early weeks after birth is in part the result of loss of EPO production by the placenta.

Anemia↗

PubMed2003

Regulation of amniotic fluid volume by intramembranous absorption in sheep: role of passive permeability and vascular endothelial growth factor.

OBJECTIVE: During long-term intravascular fluid infusion in the ovine fetus, a large increase in fetal urinary flow rate occurs while amniotic fluid volume increases only slightly because of increased intramembranous absorption. The current study tested the hypotheses that passive intramembranous permeability increases in response to fetal intravascular saline solution infusion and that the increased intramembranous absorption occurs in parallel with an increase in vascular endothelial growth factor gene expression in the amnion, chorion, and placenta. STUDY DESIGN: Chronically catheterized fetal sheep that average 126 +/- 1 (SE) days of gestation either were infused intravascularly with 7 L of normal saline solution over 3 days (n = 8 sheep) or served as time controls (n = 6 sheep). Amniotic fluid volume and fetal urinary flow rate were measured daily. Intramembranous diffusional permeability was estimated daily as being equal to the clearance of intra-amniotically injected technetium 99m. Vascular endothelial growth factor messenger RNA abundance in the amnion, chorion, and placenta was determined by Northern blot analysis. Statistical analyses included analysis of variance. RESULTS: In the infused fetuses, amniotic fluid volume and urinary flow increased (P <.01) by 891 +/- 144 mL and 3488 +/- 487 mL per day, respectively, on infusion day 3 compared with no changes over time in the control fetuses. In the infused fetuses, estimated intramembranous absorption increased by 4276 +/- 499 mL during the 3-day infusion. Intramembranous technetium 99m permeability was similar over time in the two groups. In the infused group, vascular endothelial growth factor messenger RNA levels in the amnion, chorion, and placenta increased 2- to 4-fold compared with the control group (P <.001). CONCLUSION: The up-regulation of vascular endothelial growth gene expression may mediate the increase in the intramembranous absorption that is induced by volume-loading diuresis; however, this does not occur by passive mechanisms. We speculate that vascular endothelial growth mediates the increased intramembranous absorption by increasing vesicular transport.

Absorption↗

PubMed2003

Swallowing, urine flow, and amniotic fluid volume responses to prolonged hypoxia in the ovine fetus.

OBJECTIVE: Four days of hypoxia produce an extensive fetal polyuria with little change in amniotic fluid volume in the ovine fetus. We hypothesized that fetal swallowing and intramembranous absorption would increase with prolonged hypoxia to offset the polyuria. STUDY DESIGN: After a 24-hour normoxic period, nine ovine fetuses were subjected to 4 days of hypoxia induced by lowering maternal inspired oxygen content. Seven fetuses were monitored for 5 days as normoxic time controls. Measurements included fetal swallowed volume by a computerized system with Transonic flow probes, urine production by gravity drainage, and amniotic fluid volume by an indicator dilution technique. Data were averaged over 12-hour intervals, and a three-factor repeated-measures analysis of variance was used for statistical testing. RESULTS: During days 2 to 5, arterial oxygen tension was 20.7+/-1.1 (SE) mm Hg in the normoxic and 13.9+/-0.8 mm Hg in the hypoxic fetuses (P<.0001). Urine flow was unchanged over time in the normoxic fetuses and increased gradually from 693+/-88 to 2189+/-679 mL per day during hypoxia (P<.0001). The prehypoxia swallowed volume was similar in the two groups, averaging 447+/-95 mL per day. Although transiently decreased in eight of nine hypoxic fetuses, the 12-hour average swallowed volumes were not significantly different at any time in the hypoxic versus normoxic fetuses (P=.62). Amniotic fluid volume increased in the hypoxic fetuses relative to that in the normoxic fetuses (520+/-338 mL vs -226+/-136 mL, P<.01), although the increase was small (P<.01) relative to the excess volume of urine (4269+/-1306 mL). Estimated intramembranous absorption increased from 209+/-95 mL per day during normoxia to average 1032+/-396 mL per day during hypoxia. CONCLUSIONS: The current study supports the concept that prolonged hypoxia produces a progressive fetal polyuria with relatively small changes in amniotic fluid volume. Concomitantly, hypoxia does not induce prolonged changes in fetal swallowing; rather, intramembranous absorption greatly increases, thereby preventing severe polyhydramnios.

Absorption↗

PubMed2002

Prolonged hypoxia upregulates vascular endothelial growth factor messenger RNA expression in ovine fetal membranes and placenta.

OBJECTIVE: In ovine fetuses, 4 days of hypoxia resulted in a large increase in urine flow, without the development of polyhydramnios, which suggests that intramembranous absorption of the amniotic fluid was enhanced. Because vascular endothelial growth factor is speculated to be a regulator of intramembranous absorption through increases of membrane vascularity and fluid transport, we hypothesized that hypoxia upregulated vascular endothelial growth factor gene expression in the fetal membranes. STUDY DESIGN: Five near-term ovine fetuses that were subjected to 4 days of hypoxia and 5 age-matched time controls were studied. On day 4, the amnion, chorion, and placenta were collected for cellular localization and quantification of vascular endothelial growth factor messenger RNA and for the determination of vascular endothelial growth factor molecular forms that were expressed. The data were analyzed statistically with the use of t tests and 2-factor analyses of variance. RESULTS: Vascular endothelial growth factor messenger RNA was expressed in the fetal membranes localized to the amniotic epithelium and chorionic cytotrophoblast, and to the villous cytotrophoblast of the placenta. In hypoxic fetuses, vascular endothelial growth factor messenger RNA levels in these cell layers were significantly increased compared with the controls. Five vascular endothelial growth factor molecular forms were identified with vascular endothelial growth factor(164) being the most abundant form expressed. The pattern of expression of the forms was not altered by hypoxia. CONCLUSION: In the near-term ovine fetus, hypoxia induced vascular endothelial growth factor messenger RNA expression in the amnion, chorion, and placenta. This was associated with an increase in intramembranous absorption of amniotic fluid. We speculate that the increased intramembranous absorption was mediated by a vascular endothelial growth factor-induced increase in the transport of amniotic fluid into the fetal membranes.

Animals↗

PubMed2002

Red cell mass responses to daily erythropoietin and iron injections in the ovine fetus.

OBJECTIVE: Anemic ovine fetuses supplemented with intra-amniotic iron undergo rapid expansion of red cell mass. The present study tested the hypothesis that nonanemic fetuses that were supplemented with daily intra-amniotic iron plus intravascular injections of erythropoietin would experience accelerated erythrocyte production. STUDY DESIGN: Nine late gestation ovine fetuses received 100 to 120 units of erythropoietin intravascularly plus 10 mg of iron intra-amniotically daily for 7 days (low erythropoietin dose group). Four additional fetuses received 1000 units of erythropoietin plus 10 mg iron daily for the same period (high erythropoietin dose group). Responses were compared with 9 nonsupplemented time-control fetuses. Statistical testing was by 3-factor repeated measures analysis of variance. RESULTS: Immediately after erythropoietin injection, plasma erythropoietin concentration was elevated approximately 25- and 250-fold in the low and high erythropoietin dose groups, respectively. Erythropoietin returned to basal levels by 24 hours after the injection. Plasma iron concentration increased in the low erythropoietin dose group but not in the control or high erythropoietin dose groups. Reticulocyte index increased in both erythropoietin supplemented groups but not in control fetuses. Hematocrit level increased above control by day 5 in the low erythropoietin dose group and by day 2 in the high erythropoietin dose group. Red cell mass increased significantly on supplement day 7 in the low erythropoietin dose group and on day 5 in the high erythropoietin dose group. Fetal blood gases and pH were unchanged with time in all 3 groups. CONCLUSION: Although daily combined erythropoietin and iron supplements in nonanemic ovine fetuses significantly increased circulating red cell mass in a dose-dependent manner, this increase was small relative to the rapid expansion of red cell mass previously observed after iron supplementation in fetuses with hemorrhage-induced anemia. We speculate that this difference in response may be due to a combination of rapid fetal clearance of erythropoietin plus a relative insensitivity to erythropoietin caused by the absence of other cytokines, which are elevated during fetal anemia.

Amnion↗

PubMed2002

Amniotic fluid and fetal urinary responses to severe placental insufficiency in sheep.

OBJECTIVE: Our purpose was to test the hypothesis that severe placental insufficiency leads to reductions in fetal urine production and amniotic fluid volume in late-gestation fetal sheep. STUDY DESIGN: At 0.85 of gestation, chronically catheterized fetal sheep with ligated urachus were either embolized for 5 days by repeated injection of boluses of 15-microm microspheres into the common fetal umbilical artery until fetal arterial oxygen content was reduced by 50% (n = 6) or were infused with saline solution (n = 6). Amniotic fluid volume was measured daily before embolization by means of an indicator dilution technique and by drainage at autopsy. Fetal urine production, heart rate, and mean arterial blood pressure were measured continuously for 1 hour before embolization and 1 hour after embolization each day. Fetal arterial blood gases, oxygen content, electrolytes, and osmolality were also monitored. RESULTS: Five days of placental insufficiency, which reduced fetal arterial oxygen content by 50% and arrested fetal growth, resulted in a reduced amniotic fluid volume without a reduction in fetal urine production. Compared with that of controls, amniotic fluid volume was reduced over the 5-day period by 547 +/- 144 mL (-62%, P <.01). Amniotic fluid composition was also altered, with a significant increase in lactate and sodium concentrations and osmolality on days 4 to 5. On days 2 to 5, there was a progressive increase in amniotic fluid osmolality above that of controls, which paralleled the changes in amniotic fluid sodium concentration (P <.05). Fetuses became hypertensive on days 2 to 4 of embolization, although this response was attenuated by day 5. CONCLUSIONS: Chronic severe placental insufficiency caused a reduction in amniotic fluid volume not attributable to reduced fetal urine production. Changes in amniotic fluid composition induced by placental insufficiency suggest an excess intramembranous absorption of amniotic fluid water, in relation to solutes, into the fetal and maternal compartments, which may lead to the development of oligohydramnios.

Amniotic Fluid↗

PubMedDate not supplied

Temporal response of plasma erythropoietin to hemorrhage in the ovine fetus.

OBJECTIVE: In previous studies of ovine fetuses, plasma erythropoietin (EPO) concentration increased 10- to 20-fold at 24 hours after hemorrhage and returned toward normal at 48 hours. The present study in fetal sheep was designed to determine in detail the time course of the hemorrhage-induced changes in plasma EPO levels and explore the relationships among EPO concentration, blood oxygen tension, and hematocrit. METHODS: Chronically catheterized, late gestation ovine fetuses (n = 12) were hemorrhaged such that 40% of their blood volume was lost over 2 hours. Plasma EPO concentration, arterial blood gases, pH, and hematocrit were determined at 0, 1, 2, 3, 4, 6, 8, 10, 12, 16, 20, 24, and 36 hours after initiating the hemorrhage. Plasma EPO concentration was determined by radioimmunoassay. Statistical analyses included analysis of variance and least squares regression. RESULTS: Mean plasma EPO concentration increased significantly (2.3 +/- 0.5/+/- standard error of the mean/times basal values) at 4 hours after initiating the hemorrhage, reached a maximum (33.8 +/- 12.9 times basal values) at 10-16 hours, and decreased to 50% of maximal values at 24 hours after hemorrhage. Hematocrit decreased rapidly during the 12 hours after hemorrhage (P < .0001), whereas arterial blood oxygen tension remained unchanged. The logarithm of EPO concentration was correlated with hematocrit (r = -0.74, P < .0001) but not with arterial blood oxygen tension. CONCLUSIONS: Blood EPO concentration began to increase at approximately 3-4 hours after the onset of hemorrhage. Further, EPO concentrations at 24 hours after hemorrhage represented only 50% of the maximal EPO response. The correlation between EPO and hematocrit suggests that blood oxygen content rather than oxygen tension is the more important stimulant for augmented EPO production after fetal hemorrhage.

Animals↗

PubMedDate not supplied

Pulmonary elastin synthesis and deposition in developing and mature sheep: effects of intrauterine growth restriction.

Hypoxia and nutrient restriction during gestation restrict fetal growth and alter lung development. As elastin is intimately involved in lung development, our aim was to assess pulmonary elastin synthesis and deposition following intrauterine growth restriction (IUGR) induced by umbilicoplacental embolization (UPE). Pulmonary tropoelastin expression and elastin content were examined at 128 days (5 days UPE) and 140 days (20 days UPE) of the 147- days gestation and at 8 weeks and 2.3 years after birth (both approximately 27 days UPE) in sheep. UPE induced hypoxemia, hypoglycemia, and fetal growth restriction but did not affect pulmonary tropoelastin mRNA levels or elastin deposition at any age; furthermore, elastin content was unaltered apart from being lower at 140 days. The authors conclude that hypoxemia and undernutrition associated with IUGR do not affect elastin synthesis and deposition in fetal lungs; alterations in lung structure following IUGR must have other causes.

Animals↗