Drosophila immunity: the Drosocin gene encodes two host defence peptides with pathogen-specific roles.

Antimicrobial peptides (AMPs) are key to defence against infection in plants and animals. Use of AMP mutations in Drosophila has now revealed that AMPs can additively or synergistically contribute to defence in vivo. However, these studies also revealed high specificity, wherein just one AMP contributes an outsized role in combatting a specific pathogen. Here, we show the Drosocin locus (CG10816) is more complex than previously described. In addition to its namesake peptide 'Drosocin', it encodes a second mature peptide from a precursor via furin cleavage. This peptide corresponds to the previously uncharacterized 'Immune-induced Molecule 7'. A polymorphism (Thr52Ala) in the Drosocin precursor protein previously masked the identification of this peptide, which we name 'Buletin'. Using mutations differently affecting Drosocin and Buletin, we show that only Drosocin contributes to Drosocin gene-mediated defence against Enterobacter cloacae. Strikingly, we observed that Buletin, but not Drosocin, contributes to the Drosocin gene-mediated defence against Providencia burhodogranariea, including an importance of the Thr52Ala polymorphism for survival. Our study reveals that the Drosocin gene encodes two prominent host defence peptides with different specificity against distinct pathogens. This finding emphasizes the complexity of the Drosophila humoral response and demonstrates how natural polymorphisms can affect host susceptibility.

Early developmental conditioning of later health and disease: physiology or pathophysiology?

Extensive experimental animal studies and epidemiological observations have shown that environmental influences during early development affect the risk of later pathophysiological processes associated with chronic, especially noncommunicable, disease (NCD). This field is recognized as the developmental origins of health and disease (DOHaD). We discuss the extent to which DOHaD represents the result of the physiological processes of developmental plasticity, which may have potential adverse consequences in terms of NCD risk later, or whether it is the manifestation of pathophysiological processes acting in early life but only becoming apparent as disease later. We argue that the evidence suggests the former, through the operation of conditioning processes induced across the normal range of developmental environments, and we summarize current knowledge of the physiological processes involved. The adaptive pathway to later risk accords with current concepts in evolutionary developmental biology, especially those concerning parental effects. Outside the normal range, effects on development can result in nonadaptive processes, and we review their underlying mechanisms and consequences. New concepts concerning the underlying epigenetic and other mechanisms involved in both disruptive and nondisruptive pathways to disease are reviewed, including the evidence for transgenerational passage of risk from both maternal and paternal lines. These concepts have wider implications for understanding the causes and possible prevention of NCDs such as type 2 diabetes and cardiovascular disease, for broader social policy and for the increasing attention paid in public health to the lifecourse approach to NCD prevention.

X chromosome drive in a widespread Palearctic woodland fly, Drosophila testacea.

Selfish genes that bias their own transmission during meiosis can spread rapidly in populations, even if they contribute negatively to the fitness of their host. Driving X chromosomes provide a clear example of this type of selfish propagation. These chromosomes have important evolutionary and ecological consequences, and can be found in a broad range of taxa including plants, mammals and insects. Here, we report a new case of X chromosome drive (X drive) in a widespread woodland fly, Drosophila testacea. We show that males carrying the driving X (SR males) sire 80-100% female offspring and possess a diagnostic X chromosome haplotype that is perfectly associated with the sex ratio distortion phenotype. We find that the majority of sons produced by SR males are sterile and appear to lack a Y chromosome, suggesting that meiotic defects involving the Y chromosome may underlie X drive in this species. Abnormalities in sperm cysts of SR males reflect that some spermatids are failing to develop properly, confirming that drive is acting during gametogenesis. By screening wild-caught flies using progeny sex ratios and a diagnostic marker, we demonstrate that the driving X is present in wild populations at a frequency of ~ 10% and that suppressors of drive are segregating in the same population. The testacea species group appears to be a hot spot for X drive, and D. testacea is a promising model to compare driving X chromosomes in closely related species, some of which may even be younger than the chromosomes themselves.

Developmental aspects of a life course approach to healthy ageing.

We examine the mechanistic basis and wider implications of adopting a developmental perspective on human ageing. Previous models of ageing have concentrated on its genetic basis, or the detrimental effects of accumulated damage, but also have raised issues about whether ageing can be viewed as adaptive itself, or is a consequence of other adaptive processes, for example if maintenance and repair processes in the period up to reproduction are traded off against later decline in function. A life course model places ageing in the context of the attainment of peak capacity for a body system, starting in early development when plasticity permits changes in structure and function induced by a range of environmental stimuli, followed by a period of decline, the rate of which depends on the peak attained as well as the later life conditions. Such path dependency in the rate of ageing may offer new insights into its modification. Focusing on musculoskeletal and cardiovascular function, we discuss this model and the possible underlying mechanisms, including endothelial function, oxidative stress, stem cells and nutritional factors such as vitamin D status. Epigenetic changes induced during developmental plasticity, and immune function may provide a common mechanistic process underlying a life course model of ageing. The life course trajectory differs in high and low resource settings. New insights into the developmental components of the life course model of ageing may lead to the design of biomarkers of later chronic disease risk and to new interventions to promote healthy ageing, with important implications for public health.

Computational modelling of amino acid exchange and facilitated transport in placental membrane vesicles.

Placental amino acid transport is required for fetal development and impaired transport has been associated with poor fetal growth. It is well known that placental amino acid transport is mediated by a broad array of specific membrane transporters with overlapping substrate specificity. However, it is not fully understood how these transporters function, both individually and as an integrated system. We propose that mathematical modelling could help in further elucidating the underlying mechanisms of how these transporters mediate placental amino acid transport. The aim of this work is to model the sodium independent transport of serine, which has been assumed to follow an obligatory exchange mechanism. However, previous amino acid uptake experiments in human placental microvillous plasma membrane vesicles have persistently produced results that are seemingly incompatible with such a mechanism; i.e. transport has been observed under zero-trans conditions, in the absence of internal substrates inside the vesicles to drive exchange. This observation raises two alternative hypotheses; (i) either exchange is not fully obligatory, or (ii) exchange is indeed obligatory, but an unforeseen initial concentration of amino acid substrate is present within the vesicle which could drive exchange. To investigate these possibilities, a mathematical model for tracer uptake was developed based on carrier mediated transport, which can represent either facilitated diffusion or obligatory exchange (also referred to as uniport and antiport mechanisms, respectively). In vitro measurements of serine uptake by placental microvillous membrane vesicles were carried out and the model applied to interpret the results based on the measured apparent Michaelis-Menten parameters Km and Vmax. In addition, based on model predictions, a new time series experiment was implemented to distinguish the hypothesised transporter mechanisms. Analysis of the results indicated the presence of a facilitated transport component, while based on the model no evidence for substantial levels of endogenous amino acids within the vesicle was found.

Placental amino acid transport may be regulated by maternal vitamin D and vitamin D-binding protein: results from the Southampton Women's Survey.

Both maternal 25-hydroxyvitamin D (25(OH)D) concentrations during pregnancy and placental amino acid transporter gene expression have been associated with development of the offspring in terms of body composition and bone structure. Several amino acid transporter genes have vitamin D response elements in their promoters suggesting the possible linkage of these two mechanisms. We aimed to establish whether maternal 25(OH)D and vitamin D-binding protein (VDBP) levels relate to expression of placental amino acid transporters. RNA was extracted from 102 placental samples collected in the Southampton Women's Survey, and gene expression was analysed using quantitative real-time PCR. Gene expression data were normalised to the geometric mean of three housekeeping genes, and related to maternal factors and childhood body composition. Maternal serum 25(OH)D and VDBP levels were measured by radioimmunoassay. Maternal 25(OH)D and VDBP levels were positively associated with placental expression of specific genes involved in amino acid transport. Maternal 25(OH)D and VDBP concentrations were correlated with the expression of specific placental amino acid transporters, and thus may be involved in the regulation of amino acid transfer to the fetus. The positive correlation of VDBP levels and placental transporter expression suggests that delivery of vitamin D to the placenta may be important. This exploratory study identifies placental amino acid transporters which may be altered in response to modifiable maternal factors and provides a basis for further studies.

Human fetal growth is constrained below optimal for perinatal survival.

OBJECTIVE: The use of fetal growth charts assumes that the optimal size at birth is at the 50(th) birth-weight centile, but interaction between maternal constraints on fetal growth and the risks associated with small and large fetal size at birth may indicate that this assumption is not valid for perinatal mortality rates. The objective of this study was to investigate the distribution and timing (antenatal, intrapartum or neonatal) of perinatal mortality and morbidity in relation to birth weight and gestational age at delivery. METHODS: Data from over 1 million births occurring at 28-43 weeks' gestation from singleton pregnancies without congenital abnormalities in the period from 2002 to 2008 were collected from The Netherlands Perinatal Registry. The distribution of perinatal mortality according to birth-weight centile and gestational age at delivery was studied. RESULTS: In the 1 170 534 pregnancies studied, there were 5075 (0.43%) perinatal deaths. The highest perinatal mortality occurred in those with a birth weight below the 2.3(rd) centile (25.4/1000 births) and the lowest mortality was in those with birth weights between the 80(th) and 84(th) centiles (2.4/1000 births), according to routinely used growth charts. Antepartum deaths were lowest in those with birth weight between the 90(th) and 95(th) centiles. Data were almost identical when the analysis was restricted to infants born at ≥ 37 weeks' gestation. CONCLUSION: From an immediate survival perspective, optimal fetal growth requires a birth weight between the 80(th) and 84(th) centiles for the population. Median birth weight in the population is, by definition, substantially lower than these centiles, implying that the majority of fetuses exhibit some form of maternal constraint on growth. This finding is consistent with adaptations that have evolved in humans in conjunction with a large head and bipedalism, to reduce the risk of obstructed delivery. These data also fit remarkably well with those on long-term adult cardiovascular and metabolic health risks, which are lowest in cases with a birth weight around the 90(th) centile.

Transgenerational effects of prenatal exposure to the 1944-45 Dutch famine.

OBJECTIVE: We previously showed that maternal under-nutrition during gestation is associated with increased metabolic and cardiovascular disease in the offspring. Also, we found increased neonatal adiposity among the grandchildren of women who had been undernourished during pregnancy. In the present study we investigated whether these transgenerational effects have led to altered body composition and poorer health in adulthood in the grandchildren. DESIGN: Historical cohort study. SETTING: Web-based questionnaire. POPULATION: The adult offspring (F2) of a cohort of men and women (F1) born around the time of the 1944-45 Dutch famine. METHODS: We approached the F2 adults through their parents. Participating F2 adults (n = 360, mean age 37 years) completed an online questionnaire. MAIN OUTCOME MEASURES: Weight, body mass index (BMI), and health in F2 adults, according to F1 prenatal famine exposure. RESULTS: Adult offspring (F2) of prenatally exposed F1 fathers had higher weights and BMIs than offspring of prenatally unexposed F1 fathers (+4.9 kg, P = 0.03; +1.6 kg/m(2), P = 0.006). No such effect was found for the F2 offspring of prenatally exposed F1 mothers. We observed no differences in adult health between the F2 generation groups. CONCLUSIONS: Offspring of prenatally undernourished fathers, but not mothers, were heavier and more obese than offspring of fathers and mothers who had not been undernourished prenatally. We found no evidence of transgenerational effects of grandmaternal under-nutrition during gestation on the health of this relatively young group, but the increased adiposity in the offspring of prenatally undernourished fathers may lead to increased chronic disease rates in the future.

Long-term statin administration to dams on high-fat diet protects not only them but also their offspring from cardiovascular risk.

We aimed to study the effects of long-term statin administration to high fat (HF)-fed female mice from the time they were weaned through to pregnancy and lactation on cardiovascular and metabolic risk factors in their HF-fed offspring. Female C57 mice on HF (45% kcal fat) were given pravastatin in their drinking water from the time they were weaned, during pregnancy and lactation. Weaned offspring were then fed an HF diet until adulthood generating the dam/offspring dietary groups HF/HF and HF plus pravastatin from the time dams were weaned, during pregnancy and lactation/HF (HF+S/HF). These groups were compared with offspring from mothers fed standard chow (control) which were then fed a control diet up to adulthood (control/control; C/C). HF+S dams showed significantly reduced total cholesterol concentrations and systolic blood pressure (SBP) versus HF dams. The reduction in total cholesterol and SBP in the HF+S dams did not restore values to those observed in the C group. Both male and female HF+S/HF offspring were significantly lighter in weight, and had lower SBP and serum cholesterol concentrations versus HF/HF. HF/HF offspring had elevated C-reactive protein levels but HF+S/HF animals of both sexes had reduced levels similar to those found in the C/C group. Long-term pravastatin administration to dams not only protects them from the deleterious effects of an HF diet, but this long-term maternal statin protection also has an equal and permanent effect in both male and female offspring up to their adult life, which is a novel finding.

Ecology-relevant bacteria drive the evolution of host antimicrobial peptides in Drosophila.

Antimicrobial peptides are host-encoded immune effectors that combat pathogens and shape the microbiome in plants and animals. However, little is known about how the host antimicrobial peptide repertoire is adapted to its microbiome. Here, we characterized the function and evolution of the Diptericin antimicrobial peptide family of Diptera. Using mutations affecting the two Diptericins (Dpt) of Drosophila melanogaster, we reveal the specific role of DptA for the pathogen Providencia rettgeri and DptB for the gut mutualist Acetobacter. The presence of DptA- or DptB-like genes across Diptera correlates with the presence of Providencia and Acetobacter in their environment. Moreover, DptA- and DptB-like sequences predict host resistance against infection by these bacteria across the genus Drosophila. Our study explains the evolutionary logic behind the bursts of rapid evolution of an antimicrobial peptide family and reveals how the host immune repertoire adapts to changing microbial environments.

Facilitated transporters mediate net efflux of amino acids to the fetus across the basal membrane of the placental syncytiotrophoblast.

Fetal growth depends on placental transfer of amino acids from maternal to fetal blood. The mechanisms of net amino acid efflux across the basal membrane (BM) of the placental syncytiotrophoblast to the fetus, although vital for amino acid transport, are poorly understood. We examined the hypothesis that facilitated diffusion by the amino acid transporters TAT1, LAT3 and LAT4 plays an important role in this process, with possible effects on fetal growth. Amino acid transfer was measured in isolated perfused human placental cotyledons (n = 5 per experiment) using techniques which distinguish between different transport processes. Placental TAT1, LAT3 and LAT4 proteins were measured, and mRNA expression levels (measured using real-time quantitative-PCR) were related to fetal and neonatal anthropometry and dual-energy X-ray absorptiometry measurements of neonatal lean mass in 102 Southampton Women's Survey (SWS) infants. Under conditions preventing transport by amino acid exchangers, all amino acids appearing in the fetal circulation were substrates of TAT1, LAT3 or LAT4. Western blots demonstrated the presence of TAT1, LAT3 and LAT4 in placental BM preparations. Placental TAT1 and LAT3 mRNA expression were positively associated with measures of fetal growth in SWS infants (P < 0.05). We provide evidence that the efflux transporters TAT1, LAT3 and LAT4 are present in the human placental BM, and may play an important role in the net efflux of amino acids to the fetus. Unlike other transporters they can increase fetal amino acid concentrations. Consistent with a role in placental amino acid transfer capacity and fetal growth TAT1 and LAT3 mRNA expression showed positive associations with infant size at birth.

Drosophila Antimicrobial Peptides and Lysozymes Regulate Gut Microbiota Composition and Abundance.

The gut microbiota affects the physiology and metabolism of animals and its alteration can lead to diseases such as gut dysplasia or metabolic disorders. Several reports have shown that the immune system plays an important role in shaping both bacterial community composition and abundance in Drosophila, and that immune deficit, especially during aging, negatively affects microbiota richness and diversity. However, there has been little study at the effector level to demonstrate how immune pathways regulate the microbiota. A key set of Drosophila immune effectors are the antimicrobial peptides (AMPs), which confer defense upon systemic infection. AMPs and lysozymes, a group of digestive enzymes with antimicrobial properties, are expressed in the gut and are good candidates for microbiota regulation. Here, we take advantage of the model organism Drosophila melanogaster to investigate the role of AMPs and lysozymes in regulation of gut microbiota structure and diversity. Using flies lacking AMPs and newly generated lysozyme mutants, we colonized gnotobiotic flies with a defined set of commensal bacteria and analyzed changes in microbiota composition and abundance in vertical transmission and aging contexts through 16S rRNA gene amplicon sequencing. Our study shows that AMPs and, to a lesser extent, lysozymes are necessary to regulate the total and relative abundance of bacteria in the gut microbiota. We also decouple the direct function of AMPs from the immune deficiency (IMD) signaling pathway that regulates AMPs but also many other processes, more narrowly defining the role of these effectors in the microbial dysbiosis observed in IMD-deficient flies upon aging. IMPORTANCE This study advances current knowledge in the field of host-microbe interactions by demonstrating that the two families of immune effectors, antimicrobial peptides and lysozymes, actively regulate the gut microbiota composition and abundance. Consequences of the loss of these antimicrobial peptides and lysozymes are exacerbated during aging, and their loss contributes to increased microbiota abundance and shifted composition in old flies. This work shows that immune effectors, typically associated with resistance to pathogenic infections, also help shape the beneficial gut community, consistent with the idea that host-symbiont interactions use the same "language" typically associated with pathogenesis.

Maternal high-fat diet: effects on offspring bone structure.

UNLABELLED: Peak bone mass is believed to partly be programmed in utero. Mouse dams and offspring were given a high-fat diet and offspring studied as adults. Female offspring from high-fat dams exhibited altered trabecular structure indicative of in utero programming. In utero nutrition has consequences in later life. INTRODUCTION: Epidemiological studies suggest that skeletal growth is programmed during intrauterine and early postnatal life. We hypothesise that development of optimal peak bone mass has, in part, a foetal origin and investigated this using a mouse model of maternal dietary fat excess. METHODS: Offspring from mouse dams fed either standard chow (C) or lifetime high-fat diet (HF) were maintained on a HF diet to adulthood. Femur samples were taken at 30 weeks of age and bone structure, adiposity and strength analysed. Sample sizes were four to six for each sex and each diet group. RESULTS: Offspring from HF-fed dams showed increased adiposity in the femur in comparison to offspring from C-fed dams. Female offspring from HF dams exhibited altered trabecular structure indicative of in utero programming. CONCLUSIONS: A maternal HF diet during pregnancy increases bone marrow adiposity and alters bone structure in their offspring.

Noninvasive fetal electrocardiography following intermittent umbilical cord occlusion in the preterm ovine fetus.

OBJECTIVE: To investigate whether a noninvasive fetal electrocardiography (fECG) system can identify cardiovascular responses to fetal hypoxaemia and validate the results using standard invasive fECG monitoring techniques. DESIGN: Prospective cohort study. SETTING: Biological research facilities at The University of Southampton. POPULATION OR SAMPLE: Late gestation ovine fetuses; n = 5. METHODS: Five fetal lambs underwent implantation of vascular catheters, umbilical cord occluder and invasive ECG chest electrodes under general anaesthesia (3% halothane/O(2)) at 119 days of gestation (term approximately 147 days of gestation). After 5 days of recovery blood pressure, blood gases, glucose and pH were monitored. At 124 and 125 days of gestation following a 10-minute baseline period a 90-second cord occlusion was applied. Noninvasive fetal ECG was recorded from maternal transabdominal electrodes using advanced signal-processing techniques, concurrently with invasive fECG recordings. MAIN OUTCOME MEASURES: Comparison of T:QRS ratios of the ECG waveform from noninvasive and invasive fECG monitoring systems. RESULTS: Our fECG monitoring system is able to demonstrate changes in waveforms during periods of hypoxaemia similar to those obtained invasively, which could indicate fetal distress. CONCLUSIONS: These findings may indicate a future use for noninvasive electrocardiography during human fetal monitoring both before and during labour in term and preterm pregnancies.

DOHaD - the challenge of translating the science to policy.

The DOHaD Society has passed its 10th birthday, so it seems an appropriate time to reflect on what has been achieved and the Society's aspirations. At the 10th International Congress in Rotterdam in November 2017, Peter Gluckman (the Society's first President) delivered a plenary lecture entitled 'DOHaD - addressing the science-policy nexus: a reality check'; in opening the Congress, Mark Hanson (second, and outgoing President) not only highlighted the success of the Society but also the challenges it now faces in achieving impact for its work in the global health arena, that is beyond the research agenda; and in assuming the role of third President, Lucilla Poston highlighted the need for the Society to grasp opportunities to change healthcare policy, while persevering with basic research and well-planned intervention studies. In this review we summarize the points made in these three presentations and issue a call to action to the membership to take up the challenge of taking the Society's work to the next level of translating science to policy.

Developmental and epigenetic pathways to obesity: an evolutionary-developmental perspective.

Although variation in individual lifestyle and genotype are important factors in explaining individual variation in the risk of developing obesity in an obesogenic environment, there is growing evidence that developmentally plastic processes also contribute. These effects are mediated at least in part through epigenetic processes. These developmental pathways do not directly cause obesity but rather alter the risk of an individual developing obesity later in life. At least two classes of developmental pathway are involved. The mismatch pathway involves the evolved adaptive responses of the developing organism to anticipated future adverse environments, which have maladaptive consequences if the environment is mismatched to that predicted. This pathway can be cued by prenatal undernutrition or stresses that lead the organism to forecast an adverse future environment and change its developmental trajectory accordingly. As a result, individuals develop with central and peripheral changes that increase their sensitivity to an obesogenic environment. It provides a model for how obesity emerges in populations in rapid transition, but also operates in developed countries. There is growing experimental evidence that this pathway can be manipulated by, for example, postnatal leptin exposure. Secondly, maternal diabetes, maternal obesity and infant overfeeding are associated with a greater risk of later obesity. Early life offers a potential point for preventative intervention.

Sex, but not maternal protein or folic acid intake, determines the fatty acid composition of hepatic phospholipids, but not of triacylglycerol, in adult rats.

The aim of the study was to investigate whether the protein and folic acid content of the maternal diet and the sex of the offspring alter the polyunsaturated fatty acid content of hepatic phospholipids and triacylglycerol (TAG). Pregnant rats were fed diets containing 18% or 9% protein with either 1 or 5mg/kg folic acid. Maternal diet did not alter hepatic lipid composition in the adult offspring. Data from each maternal dietary group were combined and reanalysed. The proportion of 18:0, 20:4n-6 and 22:6n-3 in liver phospholipids was higher in females than in males, while hepatic TAG composition did not differ between sexes. Delta5 Desaturase expression was higher in females than in males. Neither Delta5 nor Delta6 desaturase expression was related to polyunsaturated fatty acid concentrations. These results suggest that sex differences in liver phospholipid fatty acid composition may reflect primary differences in the specificity of phospholipid biosynthesis.

Developmental mismatch: consequences for later cardiorespiratory health.

Clinical and epidemiological studies have established that people who were small at birth and had poor infant growth have an increased risk of adult cardiovascular and respiratory disease, particularly if their restricted early growth is followed by accelerated childhood weight gain. This relationship extends across the normal range of infant size in a graded manner. The 'mismatch hypothesis' proposes that ill health in later life originates through developmental plastic responses made by the fetus and infant; these responses increase the risk of adult disease if the environment in childhood and adult life differs from that predicted during early development.

The carotid bodies influence growth responses to moderate maternal undernutrition in late-gestation fetal sheep.

OBJECTIVE: To determine the role of carotid sinus innervation on differential fetal organ growth during maternal nutrient restriction in late pregnancy. DESIGN: Randomised controlled study. SETTING: University research facility. SAMPLE: Thirty-nine Merino ewes. METHODS: At 113 days gestational age (dGA), fetuses were bilaterally carotid sinus denervated or sham denervated. From 118 dGA, the surgery groups were subdivided into two dietary groups, and their ewes were fed 100% of nutrient requirements or 50% until tissue collection at 140 dGA. This provided four groups (sham/control diet, sham/restricted diet, denervated/control diet and denervated/restricted diet). MAIN OUTCOME MEASURES: Fetal organ weights and hormone levels and maternal weight change during the dietary restriction. RESULTS: Adrenal glands were larger in sham/restricted diet fetuses than in sham/control diet or denervated/restricted diet fetuses (P < 0.05). Fetal adrenal weight and brain-to-liver weight ratio were positively related to maternal weight change during the nutritional challenge in sham fetuses only (P < 0.05). Fetal liver weight was negatively related to maternal weight change during nutritional challenge in sham fetuses only (P < 0.05). CONCLUSIONS: We have shown a reduction in liver growth but sparing of adrenal growth in response to moderate maternal undernutrition, which is dependent on intact carotid body innervation. This suggests a new role for the carotid bodies in the control of differential organ growth during such undernutrition.

Fetal celiac and splenic artery flow velocity and pulsatility index: longitudinal reference ranges and evidence for vasodilation at a low portocaval pressure gradient.

OBJECTIVES: To establish longitudinal reference ranges for the fetal celiac and splenic arteries flow velocity and pulsatility index (PI), and to determine their hemodynamic relationship to venous liver perfusion and distribution and to other essential arteries. METHODS: This was a prospective longitudinal study of 161 low-risk pregnancies. Doppler recordings of the celiac and splenic arteries were made on three to five occasions at 3-5-week intervals to establish reference ranges for blood velocity and PI measurements. Peak systolic velocity in the ductus venosus, a shunt between the umbilical and inferior caval veins, was used to represent the umbilicocaval (i.e. portocaval) pressure gradient, and the left portal vein blood velocity represented the umbilical distribution to the right liver lobe. The correlations between the celiac, splenic and hepatic arteries were determined, and their association with the middle cerebral and umbilical artery PIs (MCA-PI and UA-PI) was assessed. RESULTS: Longitudinal reference ranges for the fetal celiac and splenic arteries were established based on 510 and 521 observations, respectively, during gestational weeks 21-39. Terms for calculating conditional reference ranges to be used for repeat observations are provided. Celiac and splenic artery PIs were low when portocaval pressure and umbilical supply to the right lobe were low (P < 0.0001). Their peak systolic velocity and PI were correlated (r = 0.7 (95% CI, 0.6-0.8) and r = 0.5 (95% CI, 0.3-0.6), respectively), while the PI of the hepatic artery correlated weakly with those of the celiac and splenic arteries. They were positively associated with the MCA-PI and UA-PI (P < 0.0001). CONCLUSION: We provide longitudinal reference ranges for the fetal celiac and splenic arteries Doppler measurements and show that they are involved in maintaining portal liver perfusion independently from the hepatic artery.