Differential effects of catecholamines on vascular rings from ductus venosus and intrahepatic veins of fetal sheep

Altered development of fetal liver perfusion in pregnancies with pregestational diabetes

Background

Pregestational diabetes is associated with fetal macrosomia, and umbilical perfusion of the fetal liver has a role in regulating fetal growth. We therefore hypothesized that pregestational diabetes alters fetal liver blood flow depending on degree of glycemic control.

Methods

In a prospective study, 49 women with pregestational diabetes underwent monthly ultrasound examinations during 24–36 gestational weeks. Blood flow was determined in the umbilical vein, ductus venosus and portal vein, and blood velocity was measured in the left portal vein, the latter reflecting the watershed between splanchnic and umbilical flow. The measurements were compared with reference values by z-score statistics, and the effect of HbA_1c assessed.

Results

The umbilical venous flow to the liver (z-score 0.36, p = 0.002), total venous liver flow (z-score 0.51, p<0.001) and left portal vein blood velocity (z-score 0.64, p<0.001), were higher in the study group. Normalized portal venous flow was lower (z-score -0.42, p = 0.002), and normalized total venous liver flow tended to be lower after 30 gestational weeks (z-score -0.54, p = 0.047) in the diabetic pregnancies compared with reference values from a low-risk population. The left portal vein blood velocity was positively, and the portal fraction of total venous liver flow negatively correlated with first trimester HbA_1C.

Conclusions

In spite of increased umbilical blood distribution to the fetal liver, graded according to glycemic control, the total venous liver flow did not match third trimester fetal growth in pregnancies with pregestational diabetes, thus contributing towards increased perinatal risks and possibly altered liver function with long-term metabolic consequences.

Maternal diabetes alters the development of ductus venosus shunting in the fetus

INTRODUCTION

Despite adequate glycemic control, the risks of fetal macrosomia and perinatal complications are increased in diabetic pregnancies. Adjustments of the umbilical venous distribution, including increased ductus venosus shunting, can be important fetal compensatory mechanisms, but the impact of pregestational diabetes on umbilical venous and ductus venosus flow is not known.

MATERIAL AND METHODS

In this prospective study, 49 women with pregestational diabetes mellitus underwent monthly ultrasound examinations from gestational week 20 to 36. The blood velocity and the mean diameters of the umbilical vein and ductus venosus were used for calculating blood flow volumes. The development of the umbilical venous flow, ductus venosus flow and ductus venosus shunt fraction (% of umbilical venous blood shunted through the ductus venosus) was compared with a reference population, and the effect of HbA_1c on the ductus venosus flow was assessed.

RESULTS

The umbilical venous flow was larger in pregnancies with pregestational diabetes mellitus than in low-risk pregnancies (p < 0.001) but smaller when normalized for fetal weight (p = 0.036). The distributional pattern of the ductus venosus flow developed differently in diabetic pregnancies, particularly during the third trimester, being smaller (p = 0.007), also when normalized for fetal weight (p < 0.001). Correspondingly, the ductus venosus shunt fraction was reduced (p < 0.0001), most prominently at 36 weeks. There were negative relations between the maternal HbA_1c and the ductus venosus flow velocity, flow volume and shunt fraction.

CONCLUSIONS

In pregnancies with pregestational diabetes mellitus, prioritized umbilical venous distribution to the fetal liver and lower ductus venosus shunt capacity reduce the compensatory capability of the fetus and may represent an augmented risk during hypoxic challenges during late pregnancy and birth.

The association of fetal and early childhood growth with adult mental distress: evidence from the johns hopkins collaborative perinatal study birth cohort

OBJECTIVES

Early childhood physical growth may have an impact on the development of adult mental distress. The primary objectives were to (1) assess the association of early growth in weight (adjusted for height) with adult mental distress, and (2) determine if specific sub-types, or patterns, of early physical growth are associated with adult mental distress.

METHODS

Subjects were all Johns Hopkins Collaborative Perinatal Study cohort subjects with complete birth size information that successfully completed the Pathways to Adulthood follow-up in early adulthood. Variability in the timing of growth in weight adjusted for height from birth to age 7.5 years was taken into account using a non-hierarchical linear model. Two critical periods of growth were considered as tertiles of change in weight adjusted for height from birth to age 7 and birth to age 1 year. Mental distress in adulthood (ages 29-32) was measured using the General Health Questionnaire (GHQ-28).

RESULTS

Small for gestational age subjects were at increased risk of later mental distress, but not uniformly so. Those born with low weight and length for gestational age were a distinct subgroup of those born small for gestational age, and had unique patterns of risk for adult mental distress when early growth was considered.

CONCLUSION

Acceleration and deceleration in weight for height change is associated with mental distress over multiple periods of early life and acts differentially between those periods. Furthermore, the association of early childhood growth with the likelihood of adult mental distress is dependent on prenatal growth.

Velocity profiles in the human ductus venosus: a numerical fluid structure interaction study

The veins distributing oxygenated blood from the placenta to the fetal body have been given much attention in clinical Doppler velocimetry studies, in particular the ductus venosus. The ductus venosus is embedded in the left liver lobe and connects the intra-abdominal portion of the umbilical vein (IUV) directly to the inferior vena cava, such that oxygenated blood can bypass the liver and flow directly to the fetal heart. In the current work, we have developed a mathematical model to assist the clinical assessment of volumetric flow rate at the inlet of the ductus venosus. With a robust estimate of the velocity profile shape coefficient (VC), the volumetric flow rate may be estimated as the product of the time-averaged cross-sectional area, the time-averaged cross-sectional maximum velocity and the VC. The time average quantities may be obtained from Doppler ultrasound measurements, whereas the VC may be estimated from numerical simulations. The mathematical model employs a 3D fluid structure interaction model of the bifurcation formed by the IUV, the ductus venosus and the left portal vein. Furthermore, the amniotic portion of the umbilical vein, the right liver lobe and the inferior vena cava were incorporated as lumped model boundary conditions for the fluid structure interaction model. A hyperelastic material is used to model the structural response of the vessel walls, based on recently available experimental data for the human IUV and ductus venous. A parametric study was constructed to investigate the VC at the ductus venosus inlet, based on a reference case for a human fetus at 36 weeks of gestation. The VC was found to be [Formula: see text] (Mean [Formula: see text] SD of parametric case study), which confirms previous studies in the literature on the VC at the ductus venosus inlet. Additionally, CFD simulations with rigid walls were performed on a subsection of the parametric case study, and only minor changes in the predicted VCs were observed compared to the FSI cases. In conclusion, the presented mathematical model is a promising tool for the assessment of ductus venosus Doppler velocimetry.

Fetal liver blood flow distribution: role in human developmental strategy to prioritize fat deposition versus brain development

Among primates, human neonates have the largest brains but also the highest proportion of body fat. If placental nutrient supply is limited, the fetus faces a dilemma: should resources be allocated to brain growth, or to fat deposition for use as a potential postnatal energy reserve? We hypothesised that resolving this dilemma operates at the level of umbilical blood distribution entering the fetal liver. In 381 uncomplicated pregnancies in third trimester, we measured blood flow perfusing the fetal liver, or bypassing it via the ductus venosus to supply the brain and heart using ultrasound techniques. Across the range of fetal growth and independent of the mother's adiposity and parity, greater liver blood flow was associated with greater offspring fat mass measured by dual-energy X-ray absorptiometry, both in the infant at birth (r = 0.43, P<0.001) and at age 4 years (r = 0.16, P = 0.02). In contrast, smaller placentas less able to meet fetal demand for essential nutrients were associated with a brain-sparing flow pattern (r = 0.17, p = 0.02). This flow pattern was also associated with a higher degree of shunting through ductus venosus (P = 0.04). We propose that humans evolved a developmental strategy to prioritize nutrient allocation for prenatal fat deposition when the supply of conditionally essential nutrients requiring hepatic inter-conversion is limited, switching resource allocation to favour the brain if the supply of essential nutrients is limited. Facilitated placental transfer mechanisms for glucose and other nutrients evolved in environments less affluent than those now prevalent in developed populations, and we propose that in circumstances of maternal adiposity and nutrient excess these mechanisms now also lead to prenatal fat deposition. Prenatal developmental influences play important roles in the human propensity to deposit fat.

Non-immune hydrops fetalis: a short review of etiology and pathophysiology

Hydrops fetalis is an excessive accumulation of fetal fluid. Hydrops is traditionally classified into either immune or non-immune hydrops (NIHF), but in practice, nowadays in the Western world >90% of hydrops is of non-immune origin. The basis of the disorder is an imbalance in the regulation of fetal fluid movement between the vascular and interstitial space. We previously suggested a diagnostic flow-chart for NIHF. In this short review we describe the main mechanisms leading to NIHF.

Prenatal cardiovascular shunts in amniotic vertebrates

During amniotic vertebrate development, the embryo and fetus employ a number of cardiovascular shunts. These shunts provide a right-to-left shunt of blood and are essential components of embryonic life ensuring proper blood circulation to developing organs and fetal gas exchanger, as well as bypassing the pulmonary circuit and the unventilated, fluid filled lungs. In this review we examine and compare the embryonic shunts available for fetal mammals and embryonic reptiles, including lizards, crocodilians, and birds. These groups have either a single ductus arteriosus (mammals) or paired ductus arteriosi that provide a right-to-left shunt of right ventricular output away from the unventilated lungs. The mammalian foramen ovale and the avian atrial foramina function as a right-to-left shunt of blood between the atria. The presence of atrial shunts in non-avian reptiles is unknown. Mammals have a venous shunt, the ductus venosus that diverts umbilical venous return away from the liver and towards the inferior vena cava and foramen ovale. Reptiles do not have a ductus venosus during the latter two thirds of development. While the fetal shunts are well characterized in numerous mammalian species, much less is known about the developmental physiology of the reptilian embryonic shunts. In the last years, the reactivity and the process of closure of the ductus arteriosus have been characterized in the chicken and the emu. In contrast, much less is known about embryonic shunts in the non-avian reptiles. It is possible that the single ventricle found in lizards, snakes, and turtles and the origin of the left aorta in the crocodilians play a significant role in the right-to-left embryonic shunt in these species.

Stenosis of alternative umbilical venous pathways in absence of the ductus venosus

OBJECTIVE

We evaluated fetuses with absence of the ductus venosus (ADV) and restricted alternative umbilical venous pathways.

METHODS

We identified 3 cases that fit our objective. The angles of insonation for spectral Doppler ultrasound interrogation were less than 20 degrees in all cases. We used commercially available ultrasound systems with a curved array transducer.

RESULTS

In all 3 cases, we noted mild cardiac volume overload without fetal hydrops.

CONCLUSIONS

We speculate that the fetus with ADV and a restrictive alternative umbilical venous pathway may have a more benign clinical course than fetuses previously reported with unrestricted alternative pathways.

Cardiac output and blood flow volume redistribution during acute maternal hypoxia in fetal sheep

OBJECTIVE

Acute hypoxia is one of the main causes of poor neonatal outcome. The aim of this study was the investigation of cardiac output (CO) and blood flow redistribution following induction of acute hypoxia in a fetal sheep model.

METHOD

We investigated 10 fetal sheep between 108 and 130 days of gestation. Acute hypoxia was induced by reducing the O(2) saturation in the ventilated gas mixture of the maternal sheep to approximately 75%. The CO, placental fraction of CO, Doppler parameters in the ductus venosus (DV), umbilical artery (UA) and vein (UV) were measured.

RESULTS

The fetal pO(2) decreased from 47.1 (7.19; 7.35) to 6.89 (6.78; 7.11) mm Hg [P=0.01, median, (95% CI)] during hypoxia. Fetal pH and BE were also significantly reduced. The DV/UV fraction increased from 15.3 (11.5; 19.8) to 51.1 (35.9; 62.1) (P=0.0001). The combined cardiac output [1228.1 (1024.3; 1686.4) vs. 987.8 (834, 1261) mL min(-1)], the placental fraction of the CO [31.5 (26; 42.1) vs. 26.9 (20.6; 29.3)%] and the right to left (R/L) heart ratio [1.76 (1.5; 2.2) vs. 1.3 (1.1; 1.6)] significantly decreased during hypoxia.

CONCLUSIONS

Acute hypoxia significantly increases the proportion of the placental blood passing through the DV and reduces the placental fraction of CO and the R/L heart ratio. These findings could be used as early signs of acute fetal hypoxia.

Hepatic artery hemodynamics suggest operation of a buffer response in the human fetus

After birth, the hepatic artery buffer response helps to maintain liver perfusion. Here, the authors establish a Doppler technique to measure fetal hepatic artery flow velocity and test the hypothesis that the buffer response also operates prenatally. Women with low-risk pregnancies were recruited to a longitudinal study (N = 161). Measurement techniques and reference ranges for hepatic artery velocities and pulsatility index (PI) were established. Ductus venosus peak velocity (V(DVps)) represented the portocaval pressure gradient, and umbilical venous flow (Q(UV)) represented portal flow. Reference ranges were established for the more accessible left hepatic artery branch. Hepatic artery PI was lower in fetuses with V(DVps) <10th centile (P < .05) and in those with Q(UV) <10th centile ( P < .0001). Conversely, hepatic artery PI was higher in those with Q(UV) >90th centile (P < .0001). The authors establish a method for measuring fetal hepatic arterial blood velocity, provide reference ranges, and show that the hepatic artery buffer response operates prenatally.

Dilation of the ductus venosus by stent implantation increases placental blood perfusion in fetal sheep

OBJECTIVE

The reduction of resistance to flow in the ductus venous (DV) and a decrease of blood supply to the liver serve for the survival of the fetus during hypoxia. The present study investigated the influence of the increased diameter of the DV on placental blood perfusion.

STUDY DESIGN

In 15 ewes with twin pregnancies at gestational ages of 117 +/- 4 days, a stent (4 or 5 mm) was placed into the DV of 1 twin (DV(stent) group) under ultrasound guidance. Blood flow rates in the umbilical vein (UV) and DV of both fetuses were measured using Doppler ultrasound. Eight pairs of twin fetuses were included for the final analysis.

RESULTS

The dilatation of the DV increased the blood flow volume rate passed through the DV from 136.61 +/- 41.07 to 398.93 +/- 86.62 (mL/min(-1), P < .0001) and also significantly increased placental blood perfusion from 454.35 +/- 143.0 in control twin to 663.56 +/- 167.36 in the DV(stent) group (P < .05, mL/min(-1)), respectively. The DV/UV ratio increased from 30.6 +/- 11.6% in the control group to 58.9 +/- 11.6% in DV(stent) gemini (P < .0001). The positive effect of DV dilation on the placental blood perfusion was stable and could be observed up to 3 weeks after the operation.

CONCLUSION

The dilatation of the DV by means of stent implantation in the DV increased the blood flow volume rate in the umbilical vein. Fetal surviving mechanism, the increase of DV shunting rate including redistribution of the blood flow in the liver with a reduction of DV resistance to flow, could have a second effect: the improvement of reduced placental blood perfusion during hypoxia.

Ductus venosus shunting in growth-restricted fetuses and the effect of umbilical circulatory compromise

OBJECTIVE

To determine the degree of ductus venosus (DV) shunting in fetuses with intrauterine growth restriction (IUGR) and the effect of various degrees of umbilical circulatory compromise.

METHODS

This was a cross-sectional observational study. Sixty-four fetuses with IUGR (estimated weight < or = 2.5(th) percentile) underwent ultrasound examination. The diameter, velocity, and blood flow were determined in the DV and intra-abdominal umbilical vein (UV), and the fraction of shunting and DV : UV diameter ratios were calculated. Placental compromise was classified according to either normal umbilical artery (UA) pulsatility index (PI), UA-PI > 97.5(th) percentile, or absent or reversed end-diastolic flow velocity (A/REDV). Regression analysis was used to construct mean values, and SD scores were used to determine differences compared with a reference population (n = 212) after ln- or power-transformation.

RESULTS

In the 64 growth-restricted fetuses, the average DV shunting was 39% compared with 25% in the reference group (overall P < 0.0001). The corresponding values in the subgroups with normal UA-PI, UA-PI > 97.5(th) percentile, and A/REDV were 31%, 35%, and 57%, respectively. Fetuses with IUGR and normal UA-PI (SD score: mean, 0.48; 95% CI, 0.04-0.92) did not shunt significantly more than did the reference fetuses (SD score: mean, 0.0; 95% CI, - 0.15 to 0.15), but those with UA-PI > 97.5(th) percentile (SD score: mean, 0.85; 95% CI, 0.41-1.29), and particularly those with A/REDV (SD score: mean, 1.56; 95% CI, 1.0-2.12) did shunt significantly more. With more DV shunting, these fetuses distributed correspondingly less umbilical blood to the liver, one of the mechanisms being a lower perfusion pressure as reflected in the lower DV blood velocity (P < 0.0001).

CONCLUSIONS

DV shunting is higher and the umbilical blood flow to the liver is less in fetuses with IUGR, particularly in those with the most severe umbilical hemodynamic compromise.

Ductus venosus shunting in the fetal venous circulation: regulatory mechanisms, diagnostic methods and medical importance

The fetal liver is located at the crossroads of the umbilical venous circulation. Anatomically, the ductus venosus (DV) and the intrahepatic branches of the portal vein are arranged in parallel. The actual DV shunting rate, i.e. the percentage of umbilical blood flow entering the DV measured by Doppler velocimetry, seems to be lower than that estimated using radioactively-labeled microspheres. In human fetuses the DV shunting rate is about 20-30%. Increases in the DV shunting rate are a general adaptational mechanism to fetal distress. Hypoxia results in a significant increase in the DV shunting rate, most probably in order to ensure an adequate supply of oxygen and glucose to vitally important organs such as the brain and heart. The mechanism of blood flow redistribution between the fetal liver and the DV is still a matter of debate. The isthmic portion of the DV contains less smooth muscle tissue than the intrahepatic branches of the portal vein, which in vitro react more forcefully in response to catecholamines than the DV. In growth-restricted human fetuses DV shunting is increased and the umbilical blood supply to the fetal liver is reduced. The long-term reduction of the hepatic blood supply may be involved in fetal growth restriction. The occlusion of the DV leads to a significant increase in cell proliferation in fetal skeletal muscle, heart, kidneys and liver, and possibly to an increase in insulin-like growth factor (IGF)-I and -II mRNA expression in the fetal liver. These findings hint at the possible role of the perfusion of the fetal liver in the control of the growth process. The quantification of DV shunting by Doppler velocimetry may improve the early recognition of fetal compromise in prenatal medicine. In this Review we summarize the published data on the anatomical structure and histology of the DV, the mechanisms of regulation of DV shunting, its role in fetal survival and growth and the possible use of the measurement of DV shunting in clinical practice.

The ductus venosus and intrahepatic venous system in Callithrix jacchus jacchus and Macaca fascicularis fetuses

BACKGROUND

The ductus venosus (DV) and the intrahepatic branches of the portal vein are arranged as parallel vessels. Blood shunting through the DV ensures fetal survival during periods of stress. The availability of a suitable animal model with similar structure and function to the human fetus would greatly improve the understanding of DV function. The anatomical and histological structure of the DV has not been thoroughly investigated in non-human primate species.

METHODS

Morphological investigations were performed on eight marmoset (Callithrix jacchus jacchus) at 112.5 +/- 5.5 days gestational age (mean +/- SEM) and four near-term (165 days) cynomolgus (Macaca fascicularis) fetuses.

RESULTS

The DV drains into the collectus venosus. An asymmetrical muscular lip forms a contractile element of the isthmic portion of the DV. A spherical 'dividing' eminence was found on the dorsal wall of the venous collector just above the outlet of the DV in marmoset fetuses.

CONCLUSIONS

Our findings regarding the structure of the DV in cynomolgus and marmoset fetuses were generally in agreement with previous descriptions of the morpho-histological structure of the DV in human fetuses.

Physiology of the fetal circulation

Our understanding of fetal circulatory physiology is based on experimental animal data, and this continues to be an important source of new insight into developmental mechanisms. A growing number of human studies have investigated the human physiology, with results that are similar but not identical to those from animal studies. It is time to appreciate these differences and base more of our clinical approach on human physiology. Accordingly, the present review focuses on distributional patterns and adaptational mechanisms that were mainly discovered by human studies. These include cardiac output, pulmonary and placental circulation, fetal brain and liver, venous return to the heart, and the fetal shunts (ductus venosus, foramen ovale and ductus arteriosus). Placental compromise induces a set of adaptational and compensational mechanisms reflecting the plasticity of the developing circulation, with both short- and long-term implications. Some of these aspects have become part of the clinical physiology of today with consequences for surveillance and treatment.

Effect of decreased umbilical blood flow and hemorrhage, and decreased prostaglandins on the ductus venosus diameter in the rat

BACKGROUND

The closing mechanisms of the ductus venosus (DV) have not yet been revealed.

OBJECTIVES

The aims of this study were to document the perinatal closing process of the DV, to study the suppression of prostaglandins by indomethacin, and to determine the effects of umbilical blood flow to the fetal DV.

METHODS

The proximal and distal DV diameters were studied in near-term fetal and neonatal rats with the rapid whole-body freezing method.

RESULTS

The DV diameter changed sensitively at birth, and decreased by 10% immediately after the cessation of the umbilical circulation. Umbilical hemorrhage caused an additional decrease in the DV diameter compared with neonate without the hemorrhage. The neonates showed a DV diameter decreased by 20% at 30 min and 30% at 60 min after birth. The fetal DV was tubular, and the neonatal DV was horn-shaped with a smaller inlet than outlet. A small dose (0.1 mg/kg) of indomethacin administered to the pregnant rats induced a reduction in prostaglandins and decreased the fetal DV diameter to 80% of the control. Indomethacin at a large dose (10 mg/kg), administered to the dams, induced a reduction in prostaglandins, severe constriction of the ductus arteriosus, and decreased blood flow through the descending aorta umbilicus, and caused a further reduction in the DV diameter to 70-80% of the control. A large dose of nifedipine (10 mg/kg), which causes cardiac suppression and heart failure in the fetus, was administered to near-term rats to study the effect of decreased fetal cardiac output and blood flow passing through the DV. Nifedipine induced a 20% decrease in the DV diameter for 2-8 h. In all 1-hour-old neonates with or without pretreatment, the inlet diameter of the DV was reduced more than the outlet diameter, and the DV showed a horn-shaped morphology.

CONCLUSION

In conclusion, perinatal cessation of the umbilical circulation and umbilical hemorrhage are associated with an immediate decrease in DV diameter. The DV diameter is also reduced in other conditions associated with decreased umbilical blood flow, such as induced by nifedipine which leads to heart failure and constricting of the ductus arteriosus induced by indomethacin. The constricting effect of a small dose of indomethacin suggests that prostaglandins dilate the DV physiologically.

Structural evidence for mechanisms to redistribute hepatic and ductus venosus blood flows in nonhuman primate fetuses

OBJECTIVE

The ductus venosus (DV) and the intrahepatic branches of the portal vein (BPV) play an important role in umbilical blood distribution to the fetal liver and the rest of the fetal circulation. Increased DV shunting is a major fetal survival mechanism during stress situations. The availability of a nonpregnant primate animal model with similar structure and function would greatly improve our understanding of DV function. However, the anatomic and histologic structure of the DV and the BPV have not been thoroughly investigated in any nonhuman primate species.

METHODS

Anatomic and immunohistochemical (Masson's and alpha-smooth actin stains) investigations were performed on 17 baboon fetuses at 173 +/- 5 days' gestation (mean +/- SEM, term = 180 days) (Papio sp. ) and 3 near term rhesus (Macaca mulatta) fetuses.

RESULTS

In both species the branchless, funnel-shaped DV coursed cranially, posteriorly, and slightly oblique to the left side. The DV and the efferent hepatic veins drained into a dilated ampullary area (the collectus venosus) that joined directly with the inferior cava. The length of the DV in baboons increased with gestational age ( r = 0.86, n = 16). In 4 baboon fetuses, we observed an asymmetrical muscular lip at the isthmic portion of the DV. The media of intrahepatic BPV contained more smooth muscle cells than the media of the DV.

CONCLUSION

In nonhuman primate fetuses, the DV drains into a dilated ampullary area. An asymmetrical muscular lip forms a contractile element of the isthmic portion of the DV. The increased thickness of smooth muscle tissue in the DV isthmus and intrahepatic BPV in nonhuman primate fetuses support the concept of a general organization of a contractile apparatus that performs a sphincter-like function in the central venous hepatic system and plays a key role in blood flow redistribution.

Cardiovascular development in embryos of the American alligator Alligator mississippiensis: effects of chronic and acute hypoxia

Chronic hypoxic incubation is a common tool used to address the plasticity of morphological and physiological characteristics during vertebrate development. In this study chronic hypoxic incubation of embryonic American alligators resulted in both morphological (mass) and physiological changes. During normoxic incubation embryonic mass, liver mass and heart mass increased throughout the period of study, while yolk mass fell. Chronic hypoxia(10%O2) resulted in a reduced embryonic mass at 80% and 90% of incubation. This reduction in embryonic mass was accompanied by a relative enlargement of the heart at 80% and 90% of incubation, while relative embryonic liver mass was similar to the normoxic group. Normoxic incubated alligators maintained a constant heart rate during the period of study, while mean arterial pressure rose continuously. Both levels of hypoxic incubation(15% and 10%O2) resulted in a lower mean arterial pressure at 90%of incubation, while heart rate was lower in the 10%O2 group only. Acute (5 min) exposure to 10%O2 in the normoxic group resulted in a biphasic response, with a normotensive bradycardia occurring during the period of exposure and a hypertensive tachycardic response occurring during recovery. The embryos incubated under hypoxia also showed a blunted response to acute hypoxic stress. In conclusion, the main responses elicited by chronic hypoxic incubation, namely, cardiac enlargement, blunted hypoxic response and systemic vasodilation, may provide chronically hypoxic embryos with a new physiological repertoire for responding to hypoxia.

Fetal liver-sparing cardiovascular adaptations linked to mother's slimness and diet

Fetal adaptations to impaired maternoplacental nutrient supply include altered regional blood flow. Whether such responses operate within the normal range of maternal body composition or diet is unknown, but any change in fetal liver perfusion could alter hepatic development, with long-term consequences for the risk of cardiovascular and metabolic disease. In 381 low-risk pregnancies, we found that the fetuses of slimmer mothers with lower body fat stores and those eating an unbalanced diet had greater liver blood flow and shunted less blood away from the liver through the ductus venosus at 36 weeks gestation. Consequences of such "liver-sparing" may underlie the increased cardiovascular risk of people whose mothers were slimmer and had lower body fat stores in pregnancy.

Endothelin-induced constriction of the ductus venosus in fetal sheep: developmental aspects and possible interaction with vasodilatory prostaglandin

1. The ductus venosus is actively regulated in the fetus, but questions remain on the presence of a functional sphincter at its inlet. Using fetal sheep (0.6-0.7 gestation onwards), we have examined the morphology of the vessel and have also determined whether endothelin-1 (ET-1) qualifies as a natural constrictor being modulated by prostaglandins (PGs). 2. Masson's staining and alpha-actin immunohistochemistry showed a muscular, sphincter-like formation at the ductus inlet and a muscle layer within the wall of the vessel proper. This muscle cell component increased with age. 3. ET-1 contracted dose-dependently isolated sphincter and extrasphincter preparations of the ductus from term fetus. This ET-1 effect also occurred in the premature, but its threshold was higher. 4. BQ123 (1 microm) caused a rightward shift in the ET-1 dose-response curve, while indomethacin at a threshold concentration (28 nm) tended to have an opposite effect. 5. Big ET-1 also contracted the ductus sphincter but differed from ET-1 for its lesser potency and inhibition by phosphoramidon (50 microm). 6. The ductus sphincter (term and preterm) and extrasphincter (term) released 6-keto-PGF(1alpha) (hence PGI(2)) and, to a lesser degree, PGE(2) at rest and their release increased dose-dependently upon ET-1 treatment. Both basal and stimulated release was curtailed by endothelium removal. 7. BQ123 and phosphoramidon reduced slightly the contraction of ductus sphincter to indomethacin (2.8 microm). 8. We conclude that the ductus contains a contractile mechanism in the sphincter and extrasphincter regions. ET-1 lends itself to a role in the generation of contractile tone and its action may be modulated by prostaglandins.