Trans-amniotic fetal feeding. I. Development of an animal model: continuous amniotic infusion in rabbits

Strategies for intra-amniotic administration of fetal therapy in a rabbit model of intrauterine growth restriction

Intrauterine growth restriction affects up to 10% of all pregnancies, leading to fetal programming with detrimental consequences for lifelong health. However, no therapeutic strategies have so far been effective to ameliorate these consequences. Our previous study has demonstrated that a single dose of nutrients administered into the amniotic cavity, bypassing the often dysfunctional placenta via intra-amniotic administration, improved survival at birth but not birthweight in an intrauterine growth restriction rabbit model. The aim of this study was to further develop an effective strategy for intra-amniotic fetal therapy in an animal model. Intrauterine growth restriction was induced by selective ligation of uteroplacental vessels on one uterine horn of pregnant rabbits at gestational day 25, and fetuses were delivered by cesarean section on GD30. During the five days of intrauterine growth restriction development, three different methods of intra-amniotic administration were used: continuous intra-amniotic infusion by osmotic pump, multiple intra-amniotic injections, and single fetal intraperitoneal injection. Technical feasibility, capability to systematically reach the fetus, and survival and birthweight of the derived offspring were evaluated for each technique. Continuous intra-amniotic infusion by osmotic pump was not feasible owing to the high occurrence of catheter displacement and amnion rupture, while methods using two intra-amniotic injections and one fetal intraperitoneal injection were technically feasible but compromised fetal survival. Taking into account all the numerous factors affecting intra-amniotic fetal therapy in the intrauterine growth restriction rabbit model, we conclude that an optimal therapeutic strategy with low technical failure and positive fetal impact on both survival and birthweight still needs to be found.

Nutritional intra-amniotic therapy increases survival in a rabbit model of fetal growth restriction

OBJECTIVE

To evaluate the perinatal effects of a prenatal therapy based on intra-amniotic nutritional supplementation in a rabbit model of intrauterine growth restriction (IUGR).

METHODS

IUGR was surgically induced in pregnant rabbits at gestational day 25 by ligating 40-50% of uteroplacental vessels of each gestational sac. At the same time, modified-parenteral nutrition solution (containing glucose, amino acids and electrolytes) was injected into the amniotic sac of nearly half of the IUGR fetuses (IUGR-T group n = 106), whereas sham injections were performed in the rest of fetuses (IUGR group n = 118). A control group without IUGR induction but sham injection was also included (n = 115). Five days after the ligation procedure, a cesarean section was performed to evaluate fetal cardiac function, survival and birth weight.

RESULTS

Survival was significantly improved in the IUGR fetuses that were treated with intra-amniotic nutritional supplementation as compared to non-treated IUGR animals (survival rate: controls 71% vs. IUGR 44% p = 0.003 and IUGR-T 63% vs. IUGR 44% p = 0.02), whereas, birth weight (controls mean 43g ± SD 9 vs. IUGR 36g ± SD 9 vs. IUGR-T 35g ± SD 8, p = 0.001) and fetal cardiac function were similar among the IUGR groups.

CONCLUSION

Intra-amniotic injection of a modified-parenteral nutrient solution appears to be a promising therapy for reducing mortality among IUGR. These results provide an opportunity to develop new intra-amniotic nutritional strategies to reach the fetus by bypassing the placental insufficiency.

Effect of epidermal growth factor infusion on fetal rabbit intrauterine growth retardation and small intestinal development

BACKGROUND/PURPOSE

Intrauterine growth retardation (IUGR) infants have impaired gastrointestinal function with resultant feeding difficulties and predisposition to necrotizing enterocolitis. Supplemented amniotic fluid swallowed by the developing fetus is a potential prenatal treatment for IUGR. Rabbits have naturally occurring IUGR fetuses based on uterine position. To determine intestinal response to epidermal growth factor (EGF) infusion, this rabbit model of IUGR was studied.

METHODS

Eight pregnant rabbits underwent placement of intraamniotic catheters into 2 normal and 2 IUGR fetuses per mother on gestational day 24 of a 31-day gestation. Miniosmotic pumps infused either EGF (about 300 microg/kg/d) or control solution forming 4 study groups (EGF-Favored [Fav] v. Cont-Fav; EGF-IUGR v. Cont-IUGR). On gestational day 31, the fetal gastrointestinal tracts were harvested for analysis. Intestinal epithelial cell proliferation was studied by 5-bromo-2-deoxyuridine (BrdU) incorporation, villus heights were measured, and EGF mRNA was measured by reverse transcriptase polymerase chain reaction (RT-PCR). Statistical analysis was performed using Students' t test.

RESULTS

Fetal survival rate was 87%. EGF-IUGR fetal weights were increased compared with Cont-IUGR fetuses. EGF infusion significantly increased IUGR fetal small intestinal villus height and BrdU-positive small intestinal (SI) crypt cells, all approaching Cont-Fav levels. EGF mRNA was expressed throughout the gastrointestinal tract.

CONCLUSIONS

Supplemental amniotic EGF normalizes fetal weight and intestinal proliferation in the IUGR fetal rabbit. The inclusion of EGF in supplemental amniotic feeding solutions is supported.

Prenatal tracheal ligation or intra-amniotic administration of surfactant or dexamethasone prevents some structural changes in the pulmonary arteries of surgically created diaphragmatic hernia in rabbits

PURPOSE

Characterization of the structural changes occurring in the pulmonary arteries resulting from surgically produced congenital diaphragmatic hernia in rabbits, with particular emphasis on the preventive effects of prenatal tracheal ligation or administration of intra-amniotic dexamethasone or surfactant.

METHODS

Twenty rabbit fetuses underwent surgical creation of a left-sided congenital diaphragmatic hernia on the 24th or 25th gestational day. They were divided according to the following procedures: congenital diaphragmatic hernia (n = 5), congenital diaphragmatic hernia plus tracheal ligation (n = 5), congenital diaphragmatic hernia plus intra-amniotic administration of dexamethasone 0.4 mg (n = 5) or surfactant (Curosurf 40 mg, n = 5). On gestational day 30, all the fetuses were delivered by caesarean section and killed. A control group consisted of five nonoperated fetuses. Histomorphometric analysis of medial thickness, cell nuclei density, and elastic fiber density of pulmonary arterial walls was performed.

RESULTS

Arteries with an external diameter > 100 microm have a decreased medial thickness, lower cell nuclei density, and greater elastic fiber density when compared with arteries with external diameter < or = 100 microm. Congenital diaphragmatic hernia promoted a significant decrease in medial thickness and an increase in cell nuclei density in artery walls with external diameter > 100 microm. Prenatal treatments with tracheal ligation or intra-amniotic administration of dexamethasone or surfactant prevented these changes. In arteries with external diameter < or = 100 microm, congenital diaphragmatic hernia promoted a significant increase in medial thickness and in cell nuclei density and a decrease in elastic fiber density. The prenatal treatments with tracheal ligation or intra-amniotic administration of dexamethasone or surfactant prevented these changes, although no effect was observed in elastic fiber density in the congenital diaphragmatic hernia plus dexamethasone group.

CONCLUSIONS

Congenital diaphragmatic hernia promoted different structural changes for large or small arteries. The prenatal intra-amniotic administration of dexamethasone or surfactant had positive effects on the lung structural changes promoted by congenital diaphragmatic hernia, and these effects were comparable to the changes induced by tracheal ligation.

Delayed disaccharidase development in a rabbit model of intrauterine growth retardation

Intrauterine growth retardation (IUGR) affects almost 10% of infants born in the United States. It may be responsible for delayed gastrointestinal function and is an important cause of perinatal morbidity and mortality. The New Zealand White rabbit provides an optimal model for the study of naturally occurring IUGR. At term, birth weight is determined by fetal position within the bicornuate uterus. The small intestinal disaccharidase enzymes are indicators of bowel maturity and function. To examine potential differences in disaccharidase development between normal and IUGR fetuses, this rabbit model was investigated. Jejunum was harvested at multiple stages in rabbit development including the third trimester fetus, neonate, and adult. Lactase, maltase, and sucrase enzyme activity, as well as total protein content, was determined. Results were analyzed by the 2-tailed t test and ANOVA. Lactase activity appeared in the mid-third trimester, peaked in the early neonatal period, then declined to adult levels. Maltase activity appeared in the early third trimester and gradually rose to adult levels. Sucrase remained at trace levels until the mid-neonatal period, reaching adult levels by weaning. Both lactase and maltase activity were depressed in IUGR fetuses compared with their normal littermates. This pattern of disaccharidase depression continued into the neonatal period until catch-up growth occurred at 2 wk when levels equalized. This report describes differential small intestinal disaccharidase development between normal and growth-retarded rabbit fetuses in a naturally occurring model of IUGR.

Effect of dexamethasone on insulin-like growth factor-1 expression in a rabbit model of growth retardation

BACKGROUND/PURPOSE

The maternal administration of steroids promotes fetal maturative effects in the gastrointestinal tract. To determine if fetal insulin-like growth factor-1 (IGF-1) expression is altered in response to maternal dexamethasone administration, this rabbit model of intrauterine growth retardation (IUGR) was utilized.

METHODS

Eight pregnant rabbits received either dexamethasone (Dex 0.1 mg/kg/d intramuscular), or normal saline (Cont) on gestational days 26 and 27. Fetuses were harvested on gestational day 28 or 29 and were identified as favored (Fav) or runt (Runt): DexFav, DexRunt, ContFav, and ContRunt. Fetal weight was recorded and the serum, amniotic fluid, liver, kidney, and small intestine (SI) were collected. Reverse transcription polymerase chain reaction (RT-PCR) was used to measure IGF-1/beta-actin mRNA densitometric band ratios in all tissues. Radioimmunoassay (RIA) was used to measure IGF-1 protein levels in the serum and amniotic fluid.

RESULTS

Weight was decreased in the Runt fetuses at all time-points (P < .08). The percent weight accretion from day 28 to 29, was greatest in the DexRunt fetus (P < .001), suggesting "catch-up" growth. All Dex fetuses (Fav and Runt) had increased liver and proximal, middle and distal SI IGF-1 mRNA at day 28 and elevated levels in the liver, proximal and distal SI at day 29 compared with control fetuses. The DexRunt fetuses had serum IGF-1 protein surpassing that of the DexFav fetus at day 28.

CONCLUSIONS

This report provides the first description of maternal steroid administration effecting a marked increase in fetal IGF-1 mRNA expression and IGF-1 protein levels in an in vivo rabbit model of IUGR. The growth-retarded fetus appears to be particularly responsive.

Early dietary experience influences ontogeny of intestine in response to dietary lipid changes in later life

This study was undertaken to test the hypothesis that a change in the mother's diet at the time of birth and continued during suckling modifies the intestinal transport of nutrients in the suckling offspring. Pregnant rat dams were fed one of four semisynthetic diets during pregnancy [high or low n-6/n-3 diet or a diet enriched with arachidonic acid (AA) or docosahexaenoic acid (DHA)] and were fed the same diet at the time of birth or switched to another diet. The greatest body weight gain was in the suckling rats (15-16 days of age) fed a low n-6/n-3 diet. Switching from this diet caused weight loss, and the observed weight gain with the low n-6/n-3 diet was prevented by previous exposure of the mother to the high n-6/n-3 diet or the AA- or DHA-containing diet. Although continuous feeding of a high n-6/n-3 diet to the mother during pregnancy and lactation was associated with the lowest in vitro rates of fructose uptake, switching the mother to another diet during lactation did not necessarily correct the low absorption. In contrast, continuous feeding of a high n-6/n-3 diet to the mother during pregnancy and lactation is associated with the highest maximal transport rate of glucose uptake into the jejunum and ileum. Jejunal uptake of fatty acids 12:0, 18:0, 18:3(n-3), and cholesterol was less with the low n-6/n-3 diet compared with the high n-6/n-3 diet, whereas the ileal uptake of 18:0 and 18:3(n-3) was higher with the low n-6/n-3 diet. Thus the ontogeny of the intestine is critically influenced by the mother's diet during gestation as well as during the nursing period. Some of the diet-associated changes in nutrient uptake resulting from the mother's diet during pregnancy could be corrected by dietary interventions introduced after birth.

The effects of prenatal intraamniotic surfactant or dexamethasone administration on lung development are comparable to changes induced by tracheal ligation in an animal model of congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Lung surfactant deficiency contributes to the pathophysiology of congenital diaphragmatic hernia (CDH) and the high neonatal mortality rate. Acceleration of lung surfactant system maturation by prenatal administration of hormones has been described in animal models of CDH. However, in utero tracheal ligation (TL) is the best method to accelerate lung growth and reverse the pulmonary hypoplasia associated with CDH. Although this method offers promise, its application in humans is limited. The aim of this study was to investigate a new noninvasive therapeutic strategy, that is, the prenatal intraamniotic administration of exogenous porcine surfactant or dexamethasone, and compare it with the effects of TL in an animal model of CDH.

METHODS

Twenty-four pregnant New Zealand rabbits underwent surgery on gestational day 24 or 25 to create CDH in 26 fetuses. Five groups of animals were studied: (1) Control, nonoperated fetuses (n=14), (2) CDH (n=6), (3) CDH plus TL (n 6), (4) CDH plus intraamniotic administration of Curosurf (40 mg; n=6), and (5) CDH plus intraamniotic infusion of dexamethasone (0.4 mg; n=8). On gestational day 30, the fetuses were delivered by cesarean section. Functional studies (lung hysteresis curves and lung distensibility), weight and volume of lungs, histopathologic and histomorphometric analysis of lungs were performed.

RESULTS

The authors demonstrated that the hysteresis curve of CDH animals was shifted downward in comparison with controls. The analyses of curves standardized for lung weight indicated that intraamniotic administration of surfactant or dexamethasone improved lung compliance in comparison with controls and CDH fetuses, but TL had no effect on this parameter. Lung distensibility (maximum lung volume at 32 cm of water pressure per gram of lung) was reduced by CDH, but this parameter was increased by intraamniotic administration of drugs and not by TL (P< .05). CDH decreased the weight and volume of lungs (P< .05), and these changes were reversed only by TL, which prevented the herniation of the liver from the abdomen to the thorax. Histologically, CDH lungs treated with TL or intraamniotic administration of drugs demonstrated structural patterns similar to those of controls. Histomorphometric studies proved that CDH promoted significant thickening of septa walls (P< .05), and all the therapeutic methods could reverse this alteration to control values. The alveolar number per area in control lungs, CDH, and CDH plus TL lungs were similar, but in CDH plus surfactant and CDH plus dexamethasone lungs, the decreased number per area (P< .05) demonstrated that the alveolar airspace was increased.

CONCLUSION

From these data the authors conclude that intraamniotic surfactant or dexamethasone administration is capable of preventing pulmonary hypoplasia in fetuses with CDH, and thus, this method may be a substitute for TL.

Systemic and luminal influences on the perinatal development of the gut

At birth, the mammalian gastrointestinal tract (GIT) must be able to support a shift from mainly parenteral nutrition in the fetus (via the placenta) to enteral nutrition in the neonate. In the perinatal period the GIT therefore undergoes enhanced growth as well as morphological and functional differentiation, and this maturational programme is influenced by a complex interplay of local, systemic and luminal factors. This review shows how systemic and luminal factors may influence GIT development in the perinatal period of the pig and sheep, two long-gestation species. Adrenocortical hormones play a pivotal role in the prepartum maturation of the GIT in addition to their better known effects on the development of many other tissues and body systems. More particularly, in the fetal pig and sheep, the prenatal development of gastric acid and gastrin secretion, and of GIT hydrolase activities (chymosin, pepsin, amylase, lactase, aminopeptidases) is influenced by cortisol. Additionally, glucocorticoids exert effects throughout the GIT by influencing morphological, cytological, and functional differentiation. Since the GIT epithelial cells comprise a renewing cell population there are also changes in cell kinetics. In addition to systemic factors, the presence of growth factors, hormones and nutrients from swallowed amniotic fluid (fetus) and colostrum (neonate) may influence GIT development. In utero, fetal fluid ingestion has been shown to modulate tissue growth, macromolecule and immunoglobulin transport, enterocyte differentiation, cell turnover and activity of brush-border hydrolases. These effects may be mediated via regulatory peptides (e.g. insulin-like growth factor I, gastrin-releasing peptides, insulin, epidermal growth factor, gastrin). A physiological role of luminally derived growth factors is supported by a number of unique structural and functional adaptations of the GIT in the fetus and neonate (low luminal proteolysis, intestinal macromolecule transport). Thus, in the pig and sheep, both systemic and luminal factors appear to play critical roles in GIT development in the perinatal period.

Gastroschisis increases small bowel nitric oxide synthase activity

In gastroschisis, the eviscerated fetal bowel frequently is damaged and this results in hypoperistalsis and malabsorption. The mechanistic link that ties gastroschisis-induced intestinal damage to dysfunction may be nitric oxide (NO) and the enzyme responsible for producing it, NO synthase. Using a fetal rabbit model, the authors investigated the hypothesis that the hypoperistalsis and malabsorption associated with gastroschisis may be attributable to abnormal small bowel NO synthase activity. Using the 3H-arginine-to-3H-citrulline conversion assay, they measured NO synthase activity in the small bowel of full-term fetal rabbits with and without gastroschisis. The mean total small bowel NO synthase activity of fetal rabbits with gastroschisis was 2.5 times greater than that of control littermates without gastroschisis (n = 6; 5,726 +/- 834 v 2,208 +/- 537 mean pmol/mg protein/min; P = .004). This increased NO synthase activity also was studied by measuring the individual isoforms of NO synthase, and the site of increased NO synthase activity was localized to the small bowel epithelium and neurons. After detecting and localizing the gastroschisis-induced increase in NO synthase activity, the authors explored the mechanism of this increase using NADPH-diaphorase staining. With this histological staining technique, no quantitative increase was found in the small bowel NO synthase of the rabbits with gastroschisis. This suggests that the increased NO synthase activity found in these rabbits is the result of accelerated enzyme kinetics. These findings suggest that the increased NO synthase activity caused by gastroschisis may contribute to the common clinical sequelae of malabsorption and intestinal dysmotility.

Failure of short-term luminal IGF-I to protect against atrophy in a model of fetal esophageal atresia

Short-term luminal infusion in utero (3 days) of insulin-like growth factor I (IGF-I) failed to protect the fetal small intestine against atrophy induced by ablation of swallowing. Human recombinant IGF-1 (or vehicle) was infused into the duodenum of fetal sheep at 125 days' gestation for 3 days (day 1, 0.025 mg; day 2, 0.25 mg: day 3, 2.5 mg). Fetal swallowing was prevented by esophageal ligation, and a carotid catheter was implanted for blood sampling. There were no changes in body growth of in major organ growth. Small intestinal (SI) weight (corrected for body weight) was significantly lower for IGF-I treated fetuses. Villus height decreased significantly in proximal regions. Villus enterocyte cellularity was reduced significantly in the proximal regions. The percentage of crypt cells labeled with a 4-hour pulse of tritiated thymidine (as assessed by autoradiography) decreased significantly in the proximal SI only, from 16.14% (1.06% SEM) to 13.28% (1.05% SEM) (P < .05). Plasma levels of IGF-1 increased in the treated fetuses by an average of 76%. IGF-1 immunoreactivity was detected in the apical endocytic complex of enterocytes from proximal SI. This study shows that wasting of fetal intestinal tissues in the absence of enteral input cannot be prevented by IGF-1 delivered luminally.

Wound healing in the fetal period: the resistance of the scar to rupture

Wound healing in the fetal period is fundamentally different from that of the adult. In order to better understand this difference, we have studied wound healing in three types of wounds which are the most common in surgical practice, and have paid special attention to tensile strength in the scar. A sutured wound, a nonsutured wound, and an electrocautery burn were performed on a group of 30 rabbit fetuses with a gestational age of 23 days. Seven days later, the resulting scars were examined using histological, mechanical, and biochemical studies. The results were compared with those obtained in a group of 30 newborn rabbits and in a group of 30 adult rabbits who had had the same type of wounds performed on them. The body weight of operated fetuses was smaller than their control siblings. The sutured wound in the fetuses showed a more perfect macroscopic repair than in older subjects. However, the nonsutured wounds and the burns of the fetal group did not close. In the fetuses, the tensile strength of the sutured wound was 20% of the tensile strength of healthy skin. A similar relationship occurred in the group of adult rabbits. In the sutured wound of the fetal group, the synthesis of collagen was significantly less than in the adult group. The ratio between hydroxyproline (HYP) concentration in the sutured wound and HYP concentration in healthy skin was also significantly less in the fetal group than in the adult group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of esophageal ligation on the development of fetal rabbit intestinal lactase

To investigate the effect of normal fetal swallowing and amniotic fluid ingestion on small intestinal disaccharidase development, 13 pregnant New Zealand White rabbits underwent operation on day 24 of a normal 31-day gestation. The right ovarian fetus in the bicornuate uterus underwent esophageal ligation (EL), while the contralateral left fetus underwent cervical exploration only, and served as the control (C). Rabbits were sacrificed on gestational day 31, fetal somatic measurements obtained, and the midjejunum removed for determination of disaccharidase activity and protein content. There was one maternal death, and 9 of 12 fetal pairs survived the entire study period (75%). Results are reported as mean +/- SEM, analyzed by two-tailed Student's t testing with P < .05 being considered significant. Fetal weight was decreased in EL (48.6 +/- 2.7 g) versus C (51.4 +/- 3.2 g) (P = .06). Small intestinal length decreased in EL (49.2 +/- 2.0 cm) versus C (54.9 +/- 1.1 cm) (P = .01). Midjejunal protein content (mg/mL homogenate) was also significantly decreased in EL (38.4 +/- 3.4) versus C (46.2 +/- 3.7) (P = .05). Sucrase activity was not detectable in either group. Lactase activity in jejunal mucosa was not effected when expressed as units of enzyme per milliliter of homogenate (EL = 0.357 +/- 0.03 v C = 0.373 +/- 0.04; P = .70) and units enzyme per gram of protein (EL = 38.8 +/- 4.2 v C = 34.2 +/- 4.6; P = .44). We have confirmed previous studies demonstrating decreases in somatic growth, small intestinal length, and mucosal nutrient transport in rabbit fetuses following esophageal ligation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of transamniotic administration of epidermal growth factor on fetal rabbit small intestinal nutrient transport and disaccharidase development

As fetal swallowing is documented in utero, supplementation of the ingested amniotic fluid with nutrients or hormones has been postulated as a potential prenatal treatment for intrauterine growth retardation (IUGR). To study the effect of epidermal growth factor (EGF) on the developing fetal small intestine, 12 pregnant rabbits underwent operation on day 24 of a normal 31-day gestation. Bilateral ovarian end fetuses underwent catheterization of their respective amniotic cavities with attachment to a miniosmotic pump. Study fetuses received recombinant human EGF at approximately 300 micrograms/kg/d for 1 week; controls received carrier solution only at an equivalent rate. On gestational day 31, fetuses were delivered by cesarean section and somatic measurements were recorded. The small intestine was harvested and proximal, middle, and distal regions were analyzed for lactase and maltase enzyme activity. Additionally, the uptake of radiolabeled glucose and proline was measured by a standard everted mucosal sleeve technique for each segment. Results were analyzed by Student's paired t test and reported as mean +/- SEM. Nine fetal pairs survived (75%). Small intestinal (SI) length was increased in EGF fetuses (54.8 +/- 1.9 cm) versus control (50.4 +/- 2.7 cm) (P = .02). Lactase activity, reported as UE/g protein, was significantly increased in the proximal segments in the EGF-infused fetuses; maltase was significantly increased in both the proximal and middle segments (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Gastroschisis in the partially extraamniotic fetus: experimental study

The short, thick, matted bowel, often found in gastroschisis, has been attributed to a variety of factors. We designed an original animal model in order to isolate the effect of amniotic fluid on the fetal bowel. We created experimental gastroschisis in fetal rabbits. Extruded bowel was kept out of the amniotic sac in half of the operated fetuses. At term, 7 days after surgery, 21 surviving fetuses (12 intraamniotic gastroschisis [IAG] and 9 extraamniotic gastroschisis [EAG]) and 16 control littermates were collected for study. Five parameters were measured in each animal: body weight, intestinal weight, intestinal length, bowel diameter, and bowel wall thickness. Fetal mortality due to the extraamniotic fixation technique was 25%. We found no statistically significant difference in body weight, intestinal weight, or bowel wall thickness. An enormous difference was found in intestinal length (P < .0001 among the three groups). Bowel diameter was significantly different (P = .02) in the extreme groups (IAG and controls), with the intestine being more dilated in IAG than in EAG and controls. Gastroschisis in the absence of amniotic fluid was not as damaging to the fetal intestine as "natural" intraamniotic gastroschisis.

The nutrition of the fetus with intestinal atresia: studies in the chick embryo model

This article examines the effects of experimental prenatal intestinal obstruction on the growth and blood composition of chick embryos. Intestinal atresia (IA) was produced by bipolar bowel electrocoagulation in fertile eggs on the 14th day of incubation. The chicks killed on the 19th day were measured, weighed, and blood-sampled. Twenty-three control, 10 sham-operated, and 11 IA chicks were studied. Animals with IA were severely undernourished by weight (43.4 +/- 4.7 v 70.3 +/- 7.6% of egg weight, P < .001) and length (15.3 +/- 1.1 v 18.1 +/- 0.9 mm tibial length, P < .001) in comparison with sham-operated ones. Their hematocrit was slightly lower, and total protein increased. Prealbumin was absent in their sera and albumin, alpha and beta globulins were significantly decreased, whereas gamma-globulin was greatly increased. Sodium, potassium chloride, urea, and glucose remained within normal limits. The lack of placenta in the avian embryo precludes any supply of nutrients by this route and the ingestion of amniotic fluid, which is protein-rich after the 13th day of incubation, when the opening of the seroamniotic connection allows albumen to be mixed with it, becomes the main source of nutrients until hatching. Obstruction of the main incoming avenue by IA induces severe malnutrition in this model which relies on this route to a greater extent than the human fetus. In spite of the obvious biological differences between the avian embryo and the human fetus, the present evidence supports the hypothesis that prenatal interruption of the amniotic fluid transit contributes to fetal undergrowth in IA.

Upregulation of nutrient transport in fetal rabbit intestine by transamniotic substrate administration

Delivery of nutrients to the developing fetal gastrointestinal tract has been advocated as a potential prenatal treatment for intrauterine growth retardation. To examine the effect of intrauterine nutrient administration on the uptake capacity of the intestine, 16 maternal rabbits underwent bilateral ovarian-end transamniotic catheter placement on gestational Day 24. Study fetuses received a galactose solution; the contralateral controls received mannitol, a physiologically inert carbohydrate. Infusions were continued until Day 30 when an everted sleeve technique was used to measure radiolabeled uptake of both galactose and glucose in the proximal, middle, and distal small intestine. Mucosal scrapes were obtained, weighed, and the percentage of weight was calculated. Results were analyzed by ANOVA and Student's t test with P less than 0.05 being considered significant. There were 2 maternal deaths with 11 fetal pairs surviving (79%). There was increased uptake of galactose in the study fetuses compared to controls reaching significance in the middle and distal segments. Similarly, glucose uptake was significantly increased in the proximal and distal segments. Mucosal weight was increased in all regions, reaching significance in the proximal segment. Total intestinal uptake of galactose and glucose was significantly increased in the study fetuses compared to controls. Intraamniotic galactose infusion caused not only upregulation of its own mucosal transport but also that of glucose, along the entire fetal small intestine, achieving statistical significance particularly in distal segments. Fetal implications for transamniotic feeding are under investigation.

Uptake and distribution of continuously infused intraamniotic nutrients in fetal rabbits

Nutrient delivery via the fetal gastrointestinal tract may be a potential prenatal treatment for intrauterine growth retardation. Uptake from continuous intraamniotic infusions with nutrient incorporation into developing fetal tissues has not previously been shown. To study this, ovarian-end fetuses of 18 time-mated rabbit does underwent amniotic cavity catheterization and either esophageal ligation (EL) or sham operation (SH) on gestational day 23 (term, 33 days). Saline plus 14C D-glucose and 3H proline were infused into the amniotic fluid for 4 days. Nutrients absorbed by the EL fetus represent only those taken up into the maternal circulation and subsequently redelivered hematogenously to the fetus. Radioactivity of fetal blood and organs was determined using a liquid scintillation counter. All infused does and 10 of 18 infused fetuses (56%) survived the entire study period. In SH fetuses, uptake of 14C per mg of tissue was highest in the lung and significantly greater in the stomach, jejunum, ileum, and lung than in fetal blood (P less than .05). Uptake of 3H per mg of tissue was also highest in the lung and significantly greater than fetal blood in the stomach, small intestine, lung, and liver (P less than .05). Each organ's 14C and 3H uptake was greater in SH than in EL fetuses (P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal rabbit intestinal absorption: implications for transamniotic fetal feeding

Delivery of nutrients to the fetus via the developing gastrointestinal tract has been advocated as a potential prenatal treatment for intrauterine growth retardation. Previous studies have demonstrated significant increases in fetal length and weight following continuous intraamniotic nutrient infusions in animals. The ideal composition of intraamniotic feedings has yet to be determined. Thirteen time-mated rabbit does underwent ceserean section between gestational days 27 and 33 to deliver 54 fetuses. The everted intestinal sleeve technique was used to measure radiolabeled carbohydrate and amino acid uptake rates from 1-cm segments of midjejunum. Uptake of galactose was more than double that of glucose and fructose. Active uptake of glucose, fructose, and galactose increased by 3.3-fold, 6.2-fold, and 2.1-fold, respectively, during the final 7 days of gestation when expressed as uptake per mg intestine. In contrast, uptake of the amino acids leucine, lysine, and proline decreased by 41%, 34%, and 17%, respectively, during the final 5 days of gestation. The demonstrated changes in intestinal absorption and nutrient delivery in the rabbit model, during the last days of gestation, suggest that certain substrates are absorbed more rapidly than others. Galactose may be the preferred intraamniotic carbohydrate for fetal growth.

Operative techniques in the fetal rabbit

The development of fetal surgical techniques has made the antenatal correction of congenital defects possible. These techniques have evolved from trials with animal models, permitting increasingly sophisticated operations with low morbidity and mortality. Experimental models range from large animals offering longer gestations but with single pregnancies and high cost, to smaller animals offering multiple pregnancies at reduced cost but with shorter gestations. This paper describes operative techniques in the fetal rabbit and its advantages as a fetal surgical model. Experience with the pregnant rabbit has shown it to be a suitable surgical model for several reasons. Pregnancies are multiple, increasing cost effectiveness and permitting operation on up to eight fetuses per litter without fetal loss. Techniques that promote fetal survival include local housing of does several days prior to operation and preoperative sedation. Spontaneous mask ventilation provides ease of anesthetic administration and titration. Overall surgery is well tolerated with a low incidence of intraoperative complications. Rabbit models have been used in the study of transamniotic fetal feeding, abdominal wall defects, and wound healing. These techniques have resulted in postoperative fetal viability approaching 90%, with negligible maternal mortality in over 4000 fetal operations, thereby making the rabbit a manageable cost-effective model of fetal surgery.

Transamniotic fetal feeding. II. A model of intrauterine growth retardation using the relationship of "natural runting" to uterine position

Intrauterine growth retardation (IUGR) is a leading cause of perinatal morbidity and mortality. Most IUGR is the result of inadequate transfer of nutrients from mother to fetus. Transamniotic fetal feeding (TAFF) has been proposed as a method of treating IUGR in which nutrients, infused into the amniotic fluid, would be swallowed, absorbed, and utilized by the growth retarded fetus. To study this hypothesis, we have developed a rabbit model for IUGR and TAFF. We studied the effects of maternal nutritional deprivation, uterine artery ligation, and fetal position in the uterine horn on fetal body and organ growth in 96 rabbit litters. Nutritional deprivation (n = 28) and vascular interruption (n = 34) yielded inconsistent results with high fetal mortality. We were surprised to find that fetal growth was directly and consistently related to position in the uterine horn. There is a highly significant difference (P less than .0001) in weight between siblings in the no. 1 and no. 3 positions in the rabbit uterine horn at 30 days gestation that is not present at 23 days. This "natural" runting resembles human IUGR, which occurs during the last trimester of pregnancy and shows relative brain sparing. This model, in combination with our previously reported technique for TAFF, will make possible a controlled study of the efficacy of TAFF in the treatment of IUGR.

Transamniotic fetal feeding. III. The effect of nutrient infusion on fetal growth retardation

The small-for-gestational age (SGA) infant resulting from intrauterine growth retardation (IUGR) is at high risk for perinatal complications and chronic morbidity. Most IUGR is the result of inadequate transfer of nutrients and/or oxygen from mother to fetus. Transamniotic fetal feeding (TAFF) has been proposed as a method of treating IUGR in which nutrients infused into the amniotic fluid would be swallowed, absorbed, and used by the growth retarded fetus. To study the efficacy of TAFF in the treatment of IUGR, we have previously described a rabbit model for TAFF that takes advantage of the relationship between "natural runting" (IUGR) and position on the uterine horn. We report on a controlled study of the effects of specific nutrient infusion on fetal growth retardation in this model. The infusion of dextrose, a dextrose-amino acid mixture, or lipid did not reverse or ameliorate fetal IUGR compared with controls. In addition, the infusion of lipid emulsion resulted in chronic lipid aspiration and further growth retardation. This work does not support the use of TAFF as a prenatal treatment for IUGR and suggests that oxygen may be the growth-limiting factor in most substrate deficiency IUGR. In addition, the infusion of solutions containing lipid may be harmful to the developing fetus.

Recent advances in prenatal diagnosis and treatment

This article is a summary of the prenatal and perinatal management of a variety of congenital lesions as practiced by the fetal treatment program at the University of California in San Francisco. Emphasis is placed on those lesions that are amenable to fetal intervention.

Experimental pulmonary hypoplasia due to oligohydramnios and its reversal by relieving thoracic compression

To investigate the role of thoracic compression in the etiology of pulmonary hypoplasia associated with oligohydramnios, we shunted amniotic fluid into the maternal abdominal cavity at 25-days gestation in one group of fetal rabbits and occluded the bladder outlet in another. Bladder-neck obstruction produced severe bilateral hydronephrosis. Both procedures produced oligohydramnios (amniotic fluid volume reduced, p less than .001) at reexploration on day 28. At term (day 31) newborns undergoing these procedures had significantly decreased lung weights (p less than .01). Lung histology was not affected. To determine whether decompression of the thorax would prevent pulmonary hypoplasia, another group of fetuses had their bladders occluded and underwent one of two procedures to relieve thoracic compression. In one group, amniotic fluid volume was restored by a constant infusion of normal saline. In the other, opening the abdomen and allowing viscera to herniate avoided thoracic compression from a diaphragm elevated by a dilated urinary tract and ascites. Liveborn obstructed rabbits undergoing either procedure had increased lung weight-to-body weight ratios compared to those in newborns undergoing only the obstructive procedure (p less than 0.05). These experiments suggest that mechanical restriction to lung growth plays a role in the development of pulmonary hypoplasia associated with oligohydramnios, and that pulmonary hypoplasia may be partially reversible by procedures which reduce thoracic compression.