Feeding issues in IUGR preterm infants

Measuring gut perfusion and blood flow in neonates using ultrasound Doppler of the superior mesenteric artery: a narrative review

The gut is a relatively silent organ in utero but takes on a major role after birth for the absorption and digestion of feed for adequate nutrition and growth. The neonatal circulation undergoes a transition period after birth, and gut perfusion increases rapidly to satisfy the oxygen demand and consumption. If this process is compromised at any stage, preterm and fetal growth restricted infants are at particular risk of gut tissue injury secondary to hypoxia, leading to necrotizing enterocolitis. Feeding can also be a challenge in these high-risk groups due to gut dysmotility. Superior mesenteric artery (SMA) Doppler is a safe, bedside investigation that could rapidly aid clinicians with feeding strategies and in monitoring high-risk infants. This article aims to establish normal patterns of gut blood flow velocity in neonates using SMA Doppler and reviews how it might be used clinically in pathologic states.

Gut microbiota-derived ursodeoxycholic acid alleviates low birth weight-induced colonic inflammation by enhancing M2 macrophage polarization

BACKGROUND

Low birth weight (LBW) is associated with intestinal inflammation and dysbiosis after birth. However, the underlying mechanism remains largely unknown.

OBJECTIVE

In the present study, we aimed to investigate the metabolism, therapeutic potential, and mechanisms of action of bile acids (BAs) in LBW-induced intestinal inflammation in a piglet model.

METHODS

The fecal microbiome and BA profile between LBW and normal birth weight (NBW) neonatal piglets were compared. Fecal microbiota transplantation (FMT) was employed to further confirm the linkage between microbial BA metabolism and intestinal inflammation. The therapeutic potential of ursodeoxycholic acid (UDCA), a highly differentially abundant BA between LBW and NBW piglets, in alleviating colonic inflammation was evaluated in both LBW piglets, an LBW-FMT mice model, and a DSS-induced colitis mouse model. The underlying cellular and molecular mechanisms by which UDCA suppresses intestinal inflammation were also investigated in both DSS-treated mice and a macrophage cell line. Microbiomes were analyzed by using 16S ribosomal RNA sequencing. Fecal and intestinal BA profiles were measured by using targeted BA metabolomics. Levels of farnesoid X receptor (FXR) were knocked down in J774A.1 cells with small interfering RNAs.

RESULTS

We show a significant difference in both the fecal microbiome and BA profiles between LBW and normal birth weight animals in a piglet model. Transplantation of the microbiota of LBW piglets to antibiotic-treated mice leads to intestinal inflammation. Importantly, oral administration of UDCA, a major BA diminished in the intestinal tract of LBW piglets, markedly alleviates intestinal inflammation in LBW piglets, an LBW-FMT mice model, and a mouse model of colitis by inducing M2 macrophage polarization. Mechanistically, UDCA reduces inflammatory cytokine production by engaging BA receptor FXR while suppressing NF-κB activation in macrophages.

CONCLUSIONS

These findings establish a causal relationship between LBW-associated intestinal abnormalities and dysbiosis, suggesting that restoring intestinal health and postnatal maldevelopment of LBW infants may be achieved by targeting intestinal microbiota and BA metabolism. Video Abstract.

Low Birth Weight Disturbs the Intestinal Redox Status and Mitochondrial Morphology and Functions in Newborn Piglets

Simple Summary

Low birth-weight piglets normally have a higher growth retardation and are more prone to disease such as diarrhea compared to NBW piglets, which are strongly associated with intestinal health, body redox status and mitochondrial morphology and function. The present study showed that low birth-weight piglets exhibited abnormal intestinal development and impaired intestinal barrier function and redox status when compared to normal- birth-weight piglets. Furthermore, we found that the impaired mitochondrial structure and functions may be one of the main causes of intestinal dysfunction in low birth-weight piglets. These results provided insights for the mechanisms of intestinal dysfunction in low birth-weight piglets.

Abstract

Low birth-weight (LBW) neonates exhibit a lower growth rate and impaired intestinal development. However, the reasons for abnormal development of small intestine in LBW piglets have not been widely studied. The present study focused on the redox status and mitochondrial morphology and functions of the small intestine in LBW newborn piglets. Ten newborn normal birth-weight (NBW) piglets and LBW piglets from 10 primiparous sows with the same parturition day were selected and sampled immediately without sucking colostrum. The small intestine tissues were collected and measured. Compared with NBW newborn piglets, LBW newborn piglets had a significantly decreased length and weight of the small intestine (p < 0.05) as well as the villus height/crypt depth (V/C) index in the jejunum (p < 0.05). Furthermore, LBW piglets had a lower gene expression of tight junction protein zonula occluden-1 (ZO1), claudin 1, antioxidant enzyme catalase (CAT), glutathione peroxidase (GPX) and heme oxygenase-1 (HO-1) in jejunum (p < 0.05). Meanwhile, LBW induced mitochondrial vacuolation and significantly decreased the mRNA expression of PPARγ coactivator-1α (PGC-1α) (p < 0.05) and tended to decrease the expression of cytochrome coxidase IV (Ccox IV) (p = 0.07) and cytochrome C (Cytc) (p = 0.08). In conclusion, LBW newborn piglets showed an abnormal development of the small intestine and disturbed redox status, and this may be caused by impaired morphology and the functions of mitochondria in the jejunum.

Hypoxic-ischemic enterocolitis: a proposal of a new terminology for early NEC or NEC-like disease in preterm infants, a single-center prospective observational study

We aimed to investigate the role of hypoxia-ischemia in the pathophysiology of early NEC/NEC like disease (ENEC) and classic NEC/NEC like disease (CNEC) in preterm infants. In this pilot study, preterm infants who developed the clinical symptoms and signs of NEC/NEC like disease were divided into two groups as early (≤ 7 days, ENEC) or late (> 7 days, CNEC) groups. Beside clinical variables, serum L-lactate, endothelin-1 (ET-1), platelet activating factor (PAF), and intestinal fatty acid binding protein (I-FABP) levels were measured from umbilical/peripheric venous blood in the first hour of life and during the clinical presentation in all groups. A total of 86 preterm infants were enrolled in the study. In the ENEC group, the incidences of fetal umbilical artery Doppler velocimetry abnormalities, IUGR, and delayed passage of first meconium were higher. In addition, mean levels of L-lactate, ET-1, PAF, and I-FABP were higher in the first hour of life.Conclusion: Our study firstly showed that the dominant pathophysiological factor of ENEC is prenatal hypoxic-ischemic event where intestinal injury and inflammation begin in-utero and become clinically apparent in the first week of life. Therefore, we propose a new term "Hypoxic-Ischemic Enterocolitis (HIEnt)" for the definition of ENEC in preterm infants with prenatal hemodynamic disturbances and IUGR. This new sight can provide individualized preventive and therapeutic strategies for preterm infants.What is Known:• The pathophysiology of early necrotizing enterocolitis (NEC) or NEC-like disease which is seen in the first week of life seems different than classic necrotizing enterocolitis (CNEC) which is always seen after the first week of life.What is New:• This study suggests that perinatal hypoxic-ischemic process with inflammation is the point of origin of fetal intestinal injury leading to ENEC.• We propose a new term "Hypoxic-Ischemic Enterocolitis (HIEnt)" for the definition and differentiation of this unique clinical entity.

Membrane proteomic analysis reveals the intestinal development is deteriorated by intrauterine growth restriction in piglets

The alterations of the intestinal proteome were observed in intrauterine growth restriction (IUGR) piglets during early life by gel-based approaches. Nevertheless, how IUGR affects the intestinal membrane proteome during neonatal development remains unclear. Here, we applied the iTRAQ-based proteomics technology and biochemical analysis to investigate the impact of IUGR on the membrane proteome of the jejunal mucosa in the piglets. Three hundred sixty-one membrane proteins were screened by functional prediction. Among them, eight, five, and one differentially expressed membrane proteins were identified between IUGR and NBW piglets at day 0, day 7, and day 21 after birth, respectively. Differentially expressed membrane proteins (DEMPs) including F1SBL3, F1RRW8, F1S539, F1S2Z2, F1RIR2, F1RUF2 I3LP60, Q2EN79, and F1SIH8 were reduced while the relative abundance of I3L6A2, F1SCJ1, F1RI18, I3LRJ7, and F1RNN0 were increased in IUGR piglets than NBW piglets. From the aspects of function, F1RRW8, F1S539, F1S2Z2, and F1RIR2 are mainly associated with D2 dopamine receptor binding, transmembrane transport of small molecules, signal transduction, and translocation of GLUT4, respectively, and F1SIH8, I3LRJ7, and F1RNN0 are related to autophagy, metabolism of vitamins, and intracellular protein transport. Additionally, IUGR decreased the level of proteins (F1RRW8, Q2EN79, and F1RI18) that are involved in response to oxidative stress.

Regional tissue oxygenation monitoring in the neonatal intensive care unit: evidence for clinical strategies and future directions

Near-infrared spectroscopy (NIRS)-based monitoring of regional tissue oxygenation (rSO₂) is becoming more commonplace in the neonatal intensive care unit (NICU). While increasing evidence supports rSO₂ monitoring, actual standards for applying this noninvasive bedside technique continue to evolve. This review highlights the current strengths and pitfalls surrounding practical NIRS-based monitoring in the neonatal population. The physiologic background of rSO₂ monitoring is discussed, with attention to understanding oxygen delivery/consumption mismatch and its effects on tissue oxygen extraction. The bedside utility of both cerebral and peripheral rSO₂ monitoring in the NICU is then explored from two perspectives: (1) disease/event-specific "responsive" monitoring and (2) "routine," continuous monitoring. Recent evidence incorporating both monitoring approaches is summarized with emphasis on practical applicability in the NICU. Finally, a future paradigm for a broad-based NIRS monitoring strategy is presented, with attention towards improving personalization of neonatal care and ultimately enhancing long-term outcomes.

Intrauterine Growth Restriction: Postnatal Monitoring and Outcomes

Intrauterine growth restriction (IUGR) is an important cause of fetal, perinatal and neonatal morbidity and mortality. IUGR occurs because of multiple reasons. Neonates with IUGR experience acute problems in the perinatal and early neonatal period that can be life-threatening. The unfavorable uterine environment causing growth restriction results in programming that predisposes IUGR infants to long-term health issues such as poor physical growth, metabolic syndrome, cardiovascular disease, neurodevelopmental impairment and endocrine abnormalities, warranting careful monitoring. It is imperative to strike the balance between achieving optimal catch-up to promote normal development, while preventing the onset of cardiovascular and metabolic disorders in the long-term.

Outcomes in preterm small versus appropriate for gestation infants after Bifidobacterium breve M-16 V supplementation

Introduction: Fecal bifidobacteria response after Bifidobacterium breve M-16 V supplementation was comparable in preterm small (SGA) versus appropriate for gestational age (AGA) infants.Objectives: To compare clinical outcomes between preterm SGA versus AGA infants after routine probiotic supplementation (RPS) with Bifidobacterium breve M-16V (3 × 10⁹ CFU/day).Design: Retrospective cohort study (June 2012-August 2015) comparing outcomes between preterm (<34 weeks, subgroup: <29 weeks) SGA versus AGA infants after RPS with B. breve M-16 V using multivariable regression analysis. Primary outcome: necrotizing enterocolitis (NEC)≥Stage II/all-cause mortality. Secondary outcomes: NEC ≥ Stage II, all-cause mortality, late onset sepsis (LOS), postnatal age at full feeds (PAFF).Results: Outcomes in inborn 1380/1481 (162 SGA versus 1218 AGA) admissions were analyzed. Primary outcome "NEC ≥ Stage II /all-cause mortality" was higher in SGA versus AGA infants <29 weeks (21 versus 12%; p = .040), and showed trend toward reduction (8 versus 6%; p = .057) in AGA <34 weeks. NEC ≥ Stage II, LOS, and all-cause mortality was comparable in SGA versus AGA infants <34 weeks (3 versus 2, 9 versus 8, 9% versus 6%) and <29 weeks (5 versus 4, 16 versus 9, 18% versus 19%), respectively. Median (IQR) PAFF was significantly higher in SGA versus AGA infants <34 weeks (8 (6-12) versus 7 (5-10) days), and <29 weeks (14 (12-17) versus 11 (8-16) days).Conclusions: NEC, LOS and all-cause mortality rates were similar in preterm SGA versus AGA infants after RPS with Bifidobacterium breve M-16 V, but PAFF was higher in SGA infants.

Dietary Arginine Supplementation Affects Intestinal Function by Enhancing Antioxidant Capacity of a Nitric Oxide-Independent Pathway in Low-Birth-Weight Piglets

Background

Low-birth-weight (LBW) neonates are susceptible to intestinal dysfunction. Furthermore, the antioxidant capacity of LBW neonates is significantly lower compared with that of normal-birth-weight (NBW) neonates both at birth and at weaning. In LBW neonates, dietary supplementation with arginine has shown beneficial effects on intestinal function.

Objective

The present study explored the potential mechanisms of arginine-induced protective effects against intestinal dysfunction in LBW piglets.

Methods

Forty 4-d-old LBW piglets [body weight (BW): 1.05 ± 0.04 kg] (Large White × Landrace) were assigned to 4 treatments and artificially fed a whole-milk powder- and whey protein concentrate-based diet (containing 0.65% arginine) either not supplemented with arginine (LBWC) or supplemented with 0.5%, 1.0%, or 1.5% l-arginine for 21 d. In addition, 10 NBW siblings (BW: 1.96 ± 0.03 kg) were selected and fed the basal diet. Growth performance, intestinal morphology, mRNA expression of tight junction protein, redox-sensitive genes and nitric oxide (NO) synthase, cytokines, and redox indexes were determined. Data were subjected to 1-factor ANOVA.

Results

LBW piglets exhibited poorer growth performance (29.9%), lower Claudin1 mRNA level (63.6%), lower antioxidant capacity (22.9 ∼ 24.3%), and higher jejunum interleukin 1 (IL-1) concentration (18.8%) compared with NBW piglets. Dietary supplementation with 0.5% and 1.0% l-arginine significantly enhanced daily BW gain of LBW piglets by 13.6% and 18.2%, respectively. Compared with LBWC, dietary supplementation with 1.0% l-arginine increased the serum insulin concentration (32.2%) and villus height in the jejunum (12.2%) and ileum (20.5%). In the jejunum, the mRNA levels for Claudin1 (105%) and glutathione peroxidase (36%) were higher, and the concentrations of IL-1 (31.7%) and tumor necrosis factor α (TNF-α) (30%) were lower in arginine-treated piglets than in the LBWC group. However, NO synthase activity and NO concentration in the jejunum of LBW piglets were not influenced by l-arginine supplementation.

Conclusion

The results suggested that supplementation with 1.0% l-arginine not only promoted growth performance and improved intestinal functions in LBW piglets but also improved intestinal barrier functions and enhanced antioxidant capacity by an NO-independent pathway.

Hydrogen peroxide promotes gastric motility in the newborn rat

BACKGROUND

When compared with infant formula, human milk enhances gastric emptying in preterm infants. Hydrogen peroxide (H₂O₂) is present in large quantities in human milk that has an antimicrobial role for the mother and infant. In vitro adult rat studies suggest that H₂O₂ facilitates gastric motor contraction. Hypothesizing that H₂O₂ enhances gastric motility, we investigated its effects on the newborn rat stomach tissue.

METHODS

Rat newborn and adult gastric fundic segments, or their smooth muscle cells, were used to evaluate the muscle response to H₂O₂ exposure. Tissue expression of Rho kinase 2 (ROCK-2; Western blot), its catalase activity, and H₂O₂ content (Amplex Red) were measured. H₂O₂ gastric mucosal diffusion was evaluated with Ussing chambers.

RESULTS

In both newborn and adult rats, H₂O₂ induced gastric muscle contraction and this response was attenuated by pre-incubation with the antioxidant melatonin. H₂O₂ passively diffused across the gastric mucosa. Its effect on the muscle was modulated via ROCK-2 activation and inhibited by melatonin.

CONCLUSION

H₂O₂, at a concentration similar to that of human milk, promotes gastric motility in the rat. To the extent that the present findings can be clinically extrapolated, the human milk H₂O₂ content may enhance gastric emptying in neonates.

Maternal pregnancy-induced hypertension increases subsequent neonatal necrotizing enterocolitis risk: A nationwide population-based retrospective cohort study in Taiwan

The utero-placental ischemia induced by pregnancy-induced hypertension (PIH) could lead to fetal hypoxia and proinflammatory cytokine release, which are associated with the development of neonatal necrotizing enterocolitis (NEC). However, a few studies have investigated the relationship between PIH and neonatal NEC and have produced controversial results. Therefore, we attempted to assess the relationship between PIH and the subsequent neonatal NEC risk and identify predictive risk factors.Patients with newly diagnosed PIH were recruited from the Taiwan National Health Insurance Research Database (NHIRD). For each participant, 4 age- and delivery-year-matched participants without PIH were randomly selected. A multivariable logistic regression was performed for the identification of the predictive risk factors for neonatal NEC.Among the 23.3 million individuals registered in the NHIRD, 29,013 patients with PIH and 116,052 matched controls were identified. For the multivariable analysis, maternal PIH was associated with an increased risk of subsequent neonatal NEC development (odds ratio [OR] 1.86, 95% confidence interval [CI] 1.08-3.21, P = .026). Furthermore, single parity (OR 2.06, 95% CI 1.12-3.77, P = .019), preterm birth (OR 5.97, 95% CI 3.49-10.20, P < .001), multiple gestations (OR 2.25, 95% CI 1.22-4.14, P = .010), and intrauterine growth restriction (IUGR) (OR 3.59, 95% CI 2.06-6.24, P < .001) were independent risk factors for the development of subsequent neonatal NEC.Maternal PIH increases the risk for developing neonatal NEC. Furthermore, primiparity, preterm birth, multiple gestations, and IUGR were independent risk factors for neonatal NEC.

MicroRNA-29a mediates the impairment of intestinal epithelial integrity induced by intrauterine growth restriction in pig

An important characteristic of intrauterine growth restricted (IUGR) neonate is the impaired intestinal barrier function. With the use of a pig model, this study was conducted to identify the responsible microRNA (miRNA) for the intestinal damage in IUGR neonates through comparing the miRNA profile of IUGR and normal porcine neonates and to investigate the regulation mechanism. Compared with the normal ones, we identified 83 upregulated and 76 downregulated miRNAs in the jejunum of IUGR pigs. Notably, IUGR is associated with profoundly increasesd miR-29 family and decreased expression of extracellular matrix (ECM) and tight junction (TJ) proteins in the jejunum. Furthermore, in vitro study using theporcine intestinal epithelial cell line (IPEC-1) showed that inhibition of miR-29a expression could improve the monolayer integrity by increasing cell proliferation and transepithelial resistance. Also, overexpression/inhibition of miR-29a in IPEC-1 cells can suppress/increase the expression of integrin-β1, collagen I, collagen IV, fibronectin, and claudin 1, both at transcriptional and translational levels. Subsequent luciferase reporter assay confirmed a direct interaction between miR-29a and the 3'-untranslated regions of these genes. In conclusion, this study reveals that IUGR-impaired intestinal barrier function is associated with downregulated ECM and TJ protein expression mediated by the upregulation of miR-29a.NEW & NOTEWORTHY Intrauterine growth restricted (IUGR) remains a major problem for both human health and animal production due to its association with high rates of preweaning morbidity and mortality. We have identified the abnormal expression of microRNA-29a (miR-29a) in the small intestine of IUGR neonates, as well as its targets and mechanisms. These results provide new information about biological characteristics of IUGR-affected intestinal dysfunction and can lead to the development of potentially solution for preventing and treating IUGR in the future.

Implementation of Feeding Guidelines Hastens the Time to Initiation of Enteral Feeds and Improves Growth Velocity in Very Low Birth-Weight Infants

BACKGROUND

Growth and nutrition are critical in neonatal care. Whether feeding guidelines improve growth and nutrition and reduce morbidity is unknown.

PURPOSE

Feeding guidelines for very low birth-weight (VLBW) infants were implemented in our neonatal intensive care unit (NICU) to start and achieve full enteral feeds sooner, and increase weight gain over the first month.

METHODS

Feeding guidelines for VLBW infants were implemented in January 2014, stratified by birth weight (<750, 750-1000, and 1000-1500 g). After trophic feedings, enteral feedings were advanced by 20 to 30 mL/kg/d.Data were analyzed for 2 years prior (baseline) and 6 months after (guideline) guidelines were implemented and included days to initiation of enteral feeds, days on total parenteral nutrition (TPN), and weight gain over the first month. Potential concomitant factors that could affect feeding tolerance were examined including indomethacin or dopamine treatment, delivery room cardiopulmonary resuscitation, and growth restriction.

RESULTS

A total of 95 infants with a birth weight of less than 1500 g were included (59 baseline and 36 guideline). Days to start enteral feeds decreased by 47% (P < .01) and days on TPN decreased by 25% (16 days vs 11 days; P < .01). Weight gain over the first month of life increased by 15% (p < .05). Dopamine and indomethacin use decreased during the study period, and small for gestational age infants were overrepresented in the guideline group.

IMPLICATIONS FOR PRACTICE/RESEARCH

Establishment of feeding guidelines for VLBW infants in our NICU reduced the days to start feeds and days on TPN while increasing weight gain over the first month. Improving growth and nutrition and reducing need for TPN in this vulnerable population may ultimately prevent infection and improve neurodevelopmental outcomes.

Impact of Continuous vs Bolus Feeding on Splanchnic Perfusion in Very Low Birth Weight Infants: A Randomized Trial

OBJECTIVE

To detect changes in splanchnic perfusion and oxygenation induced by 2 different feeding regimens in infants with intrauterine growth restriction (IUGR) and those without IUGR.

STUDY DESIGN

This was a randomized trial in 40 very low birth weight infants. When an enteral intake of 100 mL/kg/day was achieved, patients with IUGR and those without IUGR were randomized into 2 groups. Group A (n = 20) received a feed by bolus (in 10 minutes), then, after at least 3 hours, received the same amount of formula by continuous nutrition over 3 hours. Group B (n = 20) received a feed administered continuously over 3 hours, followed by a bolus administration (in 10 minutes) of the same amount of formula after at least 3 hours. On the day of randomization, intestinal and cerebral regional oximetry was measured via near-infrared spectroscopy and Doppler ultrasound (US) of the superior mesenteric artery was performed. Examinations were performed before the feed and at 30 minutes after the feed by bolus and before the feed, at 30 minutes after the start of the feed, and at 30 minutes after the end of the feed for the 3-hour continuous feed.

RESULTS

Superior mesenteric artery Doppler US showed significantly higher perfusion values after the bolus feeds than after the continuous feeds. Near-infrared spectroscopy values remained stable before and after feeds. Infants with IUGR and those without IUGR showed the same perfusion and oxygenation patterns.

CONCLUSION

According to our Doppler US results, bolus feeding is more effective than continuous feeding in increasing splanchnic perfusion.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01341236.

Intrauterine Growth Restriction Alters Mouse Intestinal Architecture during Development

Infants with intrauterine growth restriction (IUGR) are at increased risk for neonatal and lifelong morbidities affecting multiple organ systems including the intestinal tract. The underlying mechanisms for the risk to the intestine remain poorly understood. In this study, we tested the hypothesis that IUGR affects the development of goblet and Paneth cell lineages, thus compromising the innate immunity and barrier functions of the epithelium. Using a mouse model of maternal thromboxane A₂-analog infusion to elicit maternal hypertension and resultant IUGR, we tested whether IUGR alters ileal maturation and specifically disrupts mucus-producing goblet and antimicrobial-secreting Paneth cell development. We measured body weights, ileal weights and ileal lengths from birth to postnatal day (P) 56. We also determined the abundance of goblet and Paneth cells and their mRNA products, localization of cellular tight junctions, cell proliferation, and apoptosis to interrogate cellular homeostasis. Comparison of the murine findings with human IUGR ileum allowed us to verify observed changes in the mouse were relevant to clinical IUGR. At P14 IUGR mice had decreased ileal lengths, fewer goblet and Paneth cells, reductions in Paneth cell specific mRNAs, and decreased cell proliferation. These findings positively correlated with severity of IUGR. Furthermore, the decrease in murine Paneth cells was also seen in human IUGR ileum. IUGR disrupts the normal trajectory of ileal development, particularly affecting the composition and secretory products of the epithelial surface of the intestine. We speculate that this abnormal intestinal development may constitute an inherent “first hit”, rendering IUGR intestine susceptible to further injury, infection, or inflammation.

Physiological roles of connexins in labour and lactation

The connexin family of proteins are best known as oligomerizing to form intercellular membrane channels (gap junctions) that metabolically and ionically couple cells to allow for coordinated cellular function. Nowhere in the body is this role better illustrated than in the uterine smooth muscle during parturition, where gap junctions conduct the contraction wave throughout the tissue to deliver the baby. Parturition is followed by the onset of lactation with connexins contributing to both the dramatic reorganization of mammary gland tissue leading up to lactation and the smooth muscle contraction of the myoepithelial cells which extrudes the milk. This review summarizes what is known about the expression and roles of individual connexin family members in the uterus during labour and in the mammary glands during development and lactation. Connexin loss or malfunction in mammary glands and the uterus can have serious implications for the health of both the mother and the newborn baby.

Assessment of flow distribution in the mouse fetal circulation at late gestation by high-frequency Doppler ultrasound

This study used high-frequency ultrasound to evaluate the flow distribution in the mouse fetal circulation at late gestation. We studied 12 fetuses (embryonic day 17.5) from 12 pregnant CD1 mice with 40 MHz ultrasound to assess the flow in 11 vessels based on Doppler measurements of blood velocity and M-mode measurements of diameter. Specifically, the intrahepatic umbilical vein (UVIH), ductus venosus (DV), foramen ovale (FO), ascending aorta (AA), main pulmonary artery (MPA), ductus arteriosus (DA), descending thoracic aorta (DTA), common carotid artery (CCA), inferior vena cava (IVC), and right and left superior vena cavae (RSVC, LSVC) were examined, and anatomically confirmed by micro-CT. The mouse fetal circulatory system was found to be similar to that of the humans in terms of the major circuit and three shunts, but characterized by bilateral superior vena cavae and a single umbilical artery. The combined cardiac output (CCO) was 1.22 ± 0.05 ml/min, with the left ventricle (flow in AA) contributing 47.8 ± 2.3% and the right ventricle (flow in MPA) 52.2 ± 2.3%. Relative to the CCO, the flow percentages were 13.6 ± 1.0% for the UVIH, 10.4 ± 1.1% for the DV, 35.6 ± 2.4% for the DA, 41.9 ± 2.6% for the DTA, 3.8 ± 0.3% for the CCA, 29.5 ± 2.2% for the IVC, 12.7 ± 1.0% for the RSVC, and 9.9 ± 0.9% for the LSVC. The calculated flow percentage was 16.6 ± 3.4% for the pulmonary circulation and 31.2 ± 5.3% for the FO. In conclusion, the flow in mouse fetal circulation can be comprehensively evaluated with ultrasound. The baseline data of the flow distribution in normal mouse fetus serve as the reference range for future studies.