Biomedical subjects

C J Ashworth

Publications and source records attributed to C J Ashworth.

At least 19 recordsLinked to original sources

PubMed2006

Ovine fetal development is more sensitive to perturbation by the presence of serum in embryo culture before rather than after compaction.

The effects on subsequent fetal development of the presence or absence of serum at different times during IVC of ovine zygotes were studied. Zygotes, recovered from superovulated ewes 36h after intrauterine AI using semen from a single sire, were cultured for 5 days in synthetic oviductal fluid (SOF) media supplemented with either BSA and amino acids (SOF-) or with 10% (v/v) steer serum (SOF+). Serum was present or absent during the first two and last 2 days of IVC giving four treatments (SOF-/SOF-; SOF-/SOF+;SOF+/SOF- and SOF+/SOF+). In total, 224 embryos, including 26 in vivo controls, were transferred singly at day 6 post-AI to synchronous recipients and the products of conception recovered at day 125 of gestation. Presence of serum during IVC had a biphasic effect on embryo development. The inclusion of serum during the first 2 days of IVC retarded early embryo development while the inclusion of serum during the last 2 days of IVC produced more blastocysts by day 6. These effects were independent of each other. The presence of serum during the first 2 days of IVC resulted in increased weights of gravid uterus, placenta, fetus, fetal heart and liver. The incidence of fetuses whose total or organ weights were greater than three standard deviations above the corresponding mean weights of control fetuses was also greater when serum was present during the first 2 days of IVC. However, even when serum was absent throughout IVC there was still an infrequent incidence of fetal weights greater than three standard deviations above the mean for control fetuses. These observations provide evidence that it is the early pre-compaction stages of embryo development that are particularly sensitive to perturbations leading to abnormal fetal development.

Animals↗

PubMed2006

Zygote donor nitrogen metabolism and in vitro embryo culture perturbs in utero development and IGF2R expression in ovine fetal tissues.

Tests were made of the effects of altering nitrogen metabolism in zygote donor ewes on fetal development and expression of the gene encoding the type II insulin-like growth factor receptor (IGF2R) following the transfer of ovine embryos cultured from these zygotes, either in the absence or presence of serum. Zygotes, recovered from superovulated ewes (32 on a urea supplemented (30 g urea/kg) diet (high N) and 32 on a control diet (low N)) 36 h after intrauterine AI using semen from a single sire, were cultured for 5 days in synthetic oviductal fluid (SOF) media either with BSA and amino acids (SOF-) or with 10% (v/v) steer serum (SOF+). In total, 166 embryos, including 30 in vivo controls, were transferred singly at day 6 post-AI to synchronous recipients and the products of conception recovered at day 125 of gestation. Elevated plasma urea concentrations in zygote donors were associated with accelerated early embryo development, low pregnancy rates (16%) for embryos from the high N, SOF+ treatment, and significantly influenced fetal development and the expression of IGF2R in the fetal heart at day 125 of gestation. Importantly, the culture of sheep zygotes under serum-free conditions led to a high incidence of aberrant conceptus development and IGF2R expression. Consequently, maternal nitrogen metabolism prior to zygote recovery and in vitro culture can influence fetal development and the expression of an imprinted gene following embryo transfer, and these data support the notion that environmental effects on the follicle-enclosed oocyte may contribute to the etiology of the Large Offspring Syndrome.

Animals↗

PubMed2006

Altered muscle development and expression of the insulin-like growth factor system in growth retarded fetal pigs.

We have used a porcine model of spontaneous differential fetal growth to investigate the effects of fetal size on muscle development. We hypothesized that altered muscle development may occur in small fetuses as a consequence of modified expression of selected genes of the insulin-like growth factor system. We examined the development of the Longissimus muscle (m. Longissimus) in small fetuses and their average sized littermates. We collected small for gestational age fetuses and their average sized sibling on days 45, 65 and 100 of gestation (term is 113-116 days). Small fetuses had significantly lower body weight at all three stages of gestation (p<0.05) and significantly reduced secondary to primary muscle fibre ratio in m. Longissimus on day 100 (p<0.05) compared to their littermates. On day 65, the expression of insulin-like growth factor receptor 1 and insulin-like growth factor binding protein 3 were significantly higher (p<0.05) in m. Longissimus of the small fetuses compared with their average sized littermates. On day 100, the expression of insulin-like growth factor receptor 1 remained significantly higher (p=0.001), in addition to significantly higher levels of insulin-like growth factor receptor 2 and insulin-like growth factor binding protein 5 in the small fetuses (p<0.05). No difference in levels of myogenin was observed between the small and average sized littermates. In conclusion, we demonstrate that reduced fetal muscle development is associated with an increased expression of several genes of the insulin-like growth factor system in small fetuses in mid to late gestation.

Animals↗

PubMed2006

Effect of alterations in the quantity and composition of the pre-mating diet on embryo survival and foetal growth in the pig.

This trial examined the effects of feeding six diets, which varied in either amount or composition, during the oestrous cycle prior to insemination on embryo survival and foetal development on day 27+/-2 of pregnancy in gilts. Ten or 11 gilts per group received either a maintenance (M) diet, 1.8 x M, 2.6 x M or nutritionally balanced diets in which the content of fibre, protein or starch was increased. Of the six diets tested, only the high fibre diet significantly increased embryo survival when compared to its 1.8 x M isoenergetic control (88.20+/-1.96% versus 81.25+/-2.67%; P<0.05). More litters from gilts fed the 1.8 x M and the starch diets had foetuses defined as intra-uterine growth retarded (IUGR; 50% and 62.5 of litters, respectively), compared to the other four groups in which 0-12.5% of litters contained IUGR foetuses (P<0.05). There was no effect of dietary treatment on foetal or placental size or on the within-litter variability in foetal and placental size. Plasma concentrations of oestradiol and progesterone on days 4-8 of the oestrous cycle and on day 27+/-2 of pregnancy were unaffected by treatment. Feed intake was positively related to mean plasma IGF-1 concentrations on days 4-8 of the cycle (P<0.01) and to mean leptin concentrations on days 4 and 5 (P<0.001). Leptin concentrations were unaffected by alterations in the composition of the diet, whereas IGF-1 concentrations were higher in gilts fed the starch diet compared to the M control (159+/-9.52 versus 127+/-7.65 ng/ml; P<0.05). These data demonstrate that alteration to the composition of the feed consumed during the cycle before insemination can affect both embryo survival and the distribution of foetal size within the litter. The underlying mechanism(s) remain to be determined, but probably involve dietary-induced changes in concentrations of reproductive hormones and/or intermediary metabolites that in turn affect ovarian follicular and oocyte development.

Adipose Tissue↗

PubMed2006

Expression and adaptive regulation of amino acid transport system A in a placental cell line under amino acid restriction.

Trans-placental transport of amino acids is vital for the developing fetus. Using the BeWo cell line as a placental model, we investigated the effect of restricting amino acid availability on amino acid transport system type A. BeWo cells were cultured either in amino acid-depleted (without non-essential amino acids) or control media for 1, 3, 5 or 6 h. System A function was analysed using alpha(methyl-amino)isobutyric acid (MeAIB) transcellular transport studies. Transporter (sodium coupled neutral amino acid transporter (SNAT1/2)) expression was analysed at mRNA and protein level by Northern and Western blotting respectively. Localisation was carried out using immunocytochemistry. MeAIB transcellular transport was significantly (P < 0.05) increased by incubation of the cells in amino acid-depleted medium for 1 h, and longer incubation times caused further increases in the rate of transfer. However, the initial response was not accompanied by an increase in SNAT2 mRNA; this occurred only after 3 h and further increased for the rest of the 6-h incubation. Similarly, it took several hours for a significant increase in SNAT2 protein expression. In contrast, relocalisation of existing SNAT2 transporters occurred within 30 min of amino acid restriction and continued throughout the 6-h incubation. When the cells were incubated in medium with even lower amino acid levels (without non-essential plus 0.5 x essential amino acids), SNAT2 mRNA levels showed further significant (P < 0.0001) up-regulation. However, incubation of cells in depleted medium for 6 h caused a significant (P = 0.014) decrease in the expression of SNAT1 mRNA. System L type amino acid transporter 2 (LAT2) expression was not changed by amino acid restriction, indicating that the responses seen in the system A transporters were not a general cell response. These data have shown that placental cells adapt in vitro to nutritional stress and have identified the physiological, biochemical and genomic mechanisms involved.

Amino Acid Transport System A↗

PubMed2003

Sodium transport across the chorioallantoic membrane of porcine placenta involves the epithelial sodium channel (ENaC).

The properties of chorioallantoic membrane derived from Large White Landrace sows at 45, 65 and 100 days gestation are examined. Under short circuit conditions positive charge flows from fetal to maternal sides of the tissue. Na+ is shown to be the sole charge carrier as the short circuit current is inhibited reversibly by fetal applications of amiloride and replacement of Na+ by choline in the Ringer solution, and irreversibly by both fetal and maternal applications of ouabain. The initial short circuit current is smaller at day 100 compared to days 45 and 65. The dose responses to amiloride indicate that the epithelial sodium channel (ENaC) is involved in the movement of Na+ and that it is accessible on the fetal side of the tissue only. Immunostaining shows that the ENaC-alpha subunit is present in both the allantoic membrane and the trophoblast. Uptake studies using microvillous (apical) membrane vesicles suggest it is either inactive or only weakly active at this site. The trophoblast at day 100 has a higher content of ENaC than at days 45 and 65. This is the first report of the presence of ENaC in placental tissues. The effects of ouabain indicate the presence of a Na+ pump that is more readily inhibited by applications of the drug on the maternal aspect of the tissue than on the fetal side. Differential mechanisms may be present that would allow net movement of Na+ in either direction across the chorioallantoic membrane according to the changing demands of the developing fetus.

Amiloride↗

PubMed2003

Effect of different nutritional regimens before ovulation on plasma concentrations of metabolic and reproductive hormones and oocyte maturation in gilts.

This study examined the effect of feeding either a maintenance (1.35 kg day(-1)) or high (3.5 kg day(-1)) plane of nutrition for 19 days after oestrus on oocyte maturity and both reproductive and metabolic hormone concentrations in gilts. Blood samples were collected each day from oestrus until slaughter on day 19 and during two pulse bleeds (15 min samples for 8 h) conducted on day 12 and day 18. After slaughter, oocytes were recovered from the presumed ovulatory population of follicles, matured in vitro for 46+/-2 h with 10% of their own follicular fluid, and then fixed and stained to determine the stage of nuclear maturation of the oocyte. Gilts fed the high diet had a higher proportion of oocytes that reached metaphase II than gilts fed the maintenance diet (88.3+/-2.71% versus 68.2+/-6.48%; P=0.013). Circulating concentrations of insulin-like growth hormone I (IGF-I) and the number of LH pulses were lower (P<0.05) in gilts fed the maintenance diet compared with gilts fed the high diet on day 12 and day 18. Mean oestradiol and progesterone concentrations were higher (P<0.05) for gilts fed the maintenance diet compared with gilts fed the high diet. Leptin concentrations were also higher on day 19 in gilts fed the high diet (2.16+/-0.26 ng ml(-1) (n=9) versus 3.20+/-0.32 (n=11), P=0.025). The results of this study indicate that improved oocyte quality (increased proportion of oocytes that reached metaphase II) is associated with a number of changes in reproductive and metabolic hormones. Further studies are required to indicate which hormonal mechanism may, in turn, lead to increased embryo survival and eventual litter size.

Animal Nutritional Physiological Phenomena↗

PubMed2003

Consequences of manipulating gametes and embryos of ruminant species.

During the past 12 years, ruminants have provided a focus for some significant advances in mammalian reproductive biotechnologies. Lambs were the first offspring generated after nuclear transfer of fetal or adult cells to enucleated oocytes, and many calves of pre-determined gender are today the result of commercialized semen sexing. In 1990, the birth of one calf provided living proof that even 'dead' spermatozoa can be paternal, whereas, more recently, a short-lived gaur calf and viable mouflon lamb represented a novel option for conservation of endangered species. As well as highlights, hazards have emerged, resulting in setbacks or developmental anomalies, such as those associated with the large offspring syndrome which encompasses a range of adverse fetal, placental and post-natal phenomena expressed in ruminants. In this review, the developmental and other consequences of applying manipulative procedures, such as assisted fertilization, semen sexing, cloning and gene transfer, to gametes and embryos from bovine, ovine and caprine species are considered. Although assisted fertilization techniques can overcome mammalian infertility, they also usurp natural gamete selection safeguards, but not always with impunity. In the case of manipulations such as cloning, and to a lesser extent gene transfer, it is evident that nuclear-cytoplasmic interactions and nuclear-mitochondrial DNA interdependences are at least partially damaged or destroyed with a view to reconstruction. Therefore, among surviving zygotes and embryos it is inevitable that the legacy is frequently one of altered genetic, epigenetic or cellular programmes and processes.

Animals↗

PubMed2002

Patterns of fetal growth within Large White x Landrace and Chinese Meishan gilt litters at three stages of gestation.

Low birthweight piglets have an increased incidence of mortality and morbidity. As there are few opportunities to remedy the detrimental consequences of low birthweight after birth, it is important to understand the nature of fetal growth retardation and to identify when low birthweight fetuses deviate from the growth trajectory of their normally grown siblings. The aims of this study were to identify the nature, timing and possible causal factors influencing inadequate fetal growth in Large White x Landrace (LW) and Chinese Meishan (MS) gilts at three stages of pregnancy. Thirty-six per cent of litters contained inadequately grown fetuses. Both intrauterine-growth-restricted (IUGR) and small-for-gestational-age (SGA) fetuses could be identified as early as Day 30 in MS and LW litters and the percentage of litters containing inadequately grown fetuses was similar throughout gestation. MS fetuses, placentas and piglets had less within-litter variation in weight at all stages studied. Inverse relationships were observed between litter size and both minimum and mean weights of MS neonates. No other relationships between fetal size and either uterine position or litter size were observed.

Animals↗

PubMed2001

Feed and forage toxicants affecting embryo survival and fetal development.

Early embryonic and fetal development in mammals is sensitive to deficiencies and excesses of specific nutrients and toxicants. Operating directly and/or indirectly, these deficiencies and excesses can result in embryonic death or, in less severe circumstances, disruption of normal embryo and fetal growth. This paper explores the threats posed by feed and forage toxicants to the developing embryo and their impact on early programming of fetal development. Using significant examples, we consider the relevance of temporal sensitivities during early development in utero, and their implications for the morphology and functional competence of specific organs and tissues.

Animal Feed↗

PubMed2001

Temporal changes in reproductive hormones and conceptus-endometrial interactions during embryonic diapause and reactivation of the blastocyst in European roe deer (Capreolus capreolus).

The roe deer blastocyst is in diapause between August and December, after which time it expands and elongates rapidly before implantation. Blood samples were taken from 30 animals to define temporal changes in reproductively important hormones to investigate the physiological cues present at embryo reactivation. In 15 of these animals, changes in uterine and conceptus protein synthesis and secretion, and luteal progesterone release during diapause and reactivation, were assessed after culture of these tissues in vitro. Oestradiol concentrations remained low during diapause (1.07 +/- 0.4 pg ml(-1)) and expansion (1.2 +/- 0.4 pg ml(-1)) but increased by 30 times at trophoblast elongation (49.17 +/- 0.37 pg ml(-1)). Prolactin remained at basal concentrations (4.69 +/- 0.86 ng ml(-1)) and increased after implantation (12.34 +/- 2.71 ng ml(-1)). Peripheral progesterone concentrations and luteal progesterone release remained constant throughout diapause, reactivation and implantation (peripheral progesterone: 3.82 +/- 1.97 ng ml(-1); luteal progesterone: 6.72 +/- 0.81 ng mg(-1) protein). Incorporation of a radiolabel into conceptus secretory proteins increased by four times at expansion compared with diapause, whereas incorporation into endometrial secretions remained constant. At elongation, incorporation into endometrial secretions increased two times and conceptus secretions increased 32 times. Two-dimensional electrophoresis and fluorography showed that the profile of endometrial secretory proteins was constant until implantation when qualitative changes were evident. Although a role for an endocrine maternal trigger of reactivation from diapause cannot be dismissed, these data provide no supporting evidence and indicate that the conceptus itself may drive reactivation.

Animals↗

PubMed2001

Micronutrient programming of development throughout gestation.

Vitamins and minerals serve essential roles in cellular metabolism, maintenance and growth throughout life. They are also central components of many enzymes and transcription factors. However, the need for optimum amounts of key micronutrients at critical stages during the periovulatory period and subsequent embryonic and fetal life has become the focus of sustained research activity only recently. In addition to folic acid, the minerals zinc, iron and copper and the antioxidant vitamins A and E are of particular importance during pregnancy. Both excesses and deficiencies of these micronutrients can have profound and sometimes persistent effects on many fetal tissues and organs in the absence of clinical signs of deficiency in the mother. The consequences of micronutrient imbalance on the developing conceptus may not be apparent at the time of the nutritional insult, but may be manifest later in development. However, supplementary micronutrients provided later in gestation or during postnatal life cannot completely reverse the detrimental effects of earlier micronutrient imbalance. Importantly, deficiency of a specific micronutrient, such as zinc, during pregnancy can result in a greater incidence of fetal malformation and resorptions than general undernutrition. Given the range of micronutrients that affect development, the number of developmental stages susceptible to inappropriate micronutrient status and the diverse biochemical systems and types of tissue affected, it is challenging to propose a unifying hypothesis that could explain the effects of micronutrient imbalance on programming throughout gestation. Micronutrient imbalance can affect pregnancy outcome through alterations in maternal and conceptus metabolism, as a consequence of their essential role in enzymes and transcription factors and through their involvement in signal transduction pathways that regulate development. Micronutrient-induced disturbances in the balance between the generation of free oxygen radicals and the production of antioxidants that scavenge free radicals may provide an additional mechanistic explanation. The detrimental effects of many micronutrient deficiencies, particularly zinc and copper, can be alleviated by supplementary antioxidants, whereas deficiencies of antioxidant vitamins A and E are likely to reduce defence against free radical damage.

Animals↗

PubMed2001

Causes and consequences of fetal growth retardation in pigs.

In pigs, as in other species, fetal growth retardation is associated with reduced birth weight and increased risk of fetal and neonatal death. As there are few opportunities after birth to remedy the detrimental effects of low birth weight, it is important to understand both the intrinsic and extrinsic factors associated with inadequate fetal growth and to determine when growth retarded fetuses deviate from the growth trajectory of their normal sized littermates. Inadequately grown pig fetuses can be identified statistically as early as day 30 of the 114 days of gestation, indicating that limited uterine space is not a primary determinant of fetal growth. Comparisons of the smallest fetus within a litter with a normal sized sibling reveal that inadequately grown fetuses have altered endocrine status and lower circulating concentrations of many essential amino acids. In addition, the placenta supplying the smallest fetus is disproportionately small and has a reduced capacity to transport amino acids. Understanding the timing and the causes of fetal growth retardation in pigs may help us to devise appropriate strategies to reduce the incidence and hence the detrimental postnatal consequences of runting.

Adrenal Glands↗

PubMed2000

Placental leptin.

Placental tissues from humans, rodents and farm animals contain leptin and its receptor. Leptin produced by the human placenta has the same size, charge and immunoreactivity as leptin produced by adipose tissue. However, the expression of human placental leptin appears to be regulated by a placenta-specific upstream enhancer. In this review the occurrence of leptin and its receptor in a range of species and placental types is described, and its significance during pregnancy discussed. Placental leptin contributes to the increase in maternal circulating concentrations of leptin during late pregnancy when it is likely to have an endocrine role in regulating maternal energy balance. Placental leptin may have angiogenic and immunomodulatory activities, which affect the placenta in an autocrine or paracrine manner. It also appears to affect fetal growth and development by binding to leptin receptors present in fetal organs.

Adipose Tissue↗

PubMed2000

Moderate maternal vitamin A deficiency affects perinatal organ growth and development in rats.

Vitamin A deficiency during pregnancy is associated with detrimental effects in the offspring. We have developed a rat model to examine specific effects of maternal vitamin A status on perinatal growth and development. A total of 54 female rats were fed a vitamin A-free (VAF), -marginal (VAM) or -sufficient (VAS) diet from weaning until mating (at 7 weeks) and throughout pregnancy. Half of the rats in each group were injected with a single large dose of vitamin A on day 10 of pregnancy. Fetal and neonatal samples were taken on day 20 of pregnancy and the day of birth respectively. Maternal plasma retinol concentrations on day 20 and at birth were 50% and 30% lower in the VAF and VAM when compared to the VAS group. Fetal weight and survival did not differ between groups although placental:fetal ratio was higher in the VAF group than in the VAS group (0.195 (SE 0.005) v. 0.175 (SE 0.004), P < 0.05). Rats fed the VAF diet gave birth at 23.5 d, an average of 1 d later than the other groups, and had lower number of live neonates at birth. Fetal liver, heart and lung weights relative to total body weight were lower in the VAF group and had altered growth trajectories. In neonates, only the relative lung weight was reduced. In addition, an increased protein:DNA ratio indicated hypertrophy in fetal kidneys. Vitamin A injection had no additional effect on length of gestation and fetal or neonatal number. However, injection increased relative fetal organ weights in the VAF group but did not alter the effects of vitamin A deficiency in the neonate. These data suggest that chronic vitamin A deficiency during pregnancy compromises liver, heart and kidney and impairs lung growth and development during the last few days of gestation and reduces number of live neonates at birth.

Animals↗

PubMed1999

Effects of pre- and post-mating nutritional status on hepatic function, progesterone concentration, uterine protein secretion and embryo survival in Meishan pigs.

This experiment examined whether the pre- or the post-mating diet had greater impact on embryo survival in Meishan gilts. Gilts received either a maintenance (1.15 kg day(-1); n = 12) or a high (3.5 kg day(-1); n = 12) diet during the oestrous cycle preceding mating. After mating, half the animals in each group received either the maintenance or the high diet until slaughter on Day 12. Gilts fed the high pre-mating diet had more corpora lutea (22.7 v. 19.0, SED = 0.98; P<0.001), increased embryo survival (95.5% v. 74.8%, SED = 7.58; P<0.01) and heavier corpora lutea (-0.71 log g v. -0.90 log g, SED = 0.09; P = 0.07) compared with gilts fed the maintenance diet prior to mating. The post-mating diet had no effect on embryo survival. There were no treatment effects on blastocyst developmental stage, luteal surface area or progesterone release. Gilts receiving the high post-mating diet had heavier livers than those fed the maintenance post-mating diet (1.45 v 1.08% of total bodyweight, SED = 0.07; P<0.001), suggesting that these gilts have a greater capacity to metabolize progesterone. Pre-mating nutritional status therefore appears to be a greater determinant of embryo numbers and survival than the post-mating diet.

Acid Phosphatase↗

PubMed1999

Effects of pre- and post-mating feed intake on blastocyst size, secretory function and glucose metabolism in meishan gilts.

This experiment was designed to determine the effects of a nutritional regime, known to increase embryo survival, on blastocyst development and function. Day 12 blastocysts were recovered from Meishan gilts allocated in a 2x2 factorial design to receive either a high or a maintenance diet before or after mating (n = 4-6 gilts per group). The post-mating diet had no effect on individual blastocyst size, cell number, secretion of oestradiol-17beta or retinol binding protein, glucose metabolism or on the within-litter variability in these measures. Blastocysts recovered from gilts consuming the high pre-mating diet had more cells (13.501 v. 13.006 log cells; SED = 0.23; P = 0.05), greater production of CO2 from glucose (2.19 v. 1.23 log pmol(-1) blastocyst(-1) 3 h(-1), SED = 0.42; P = 0.05) and a lower within-litter standard deviation in blastocyst surface area (0.66 v. 1.18 log mm2, SED = 0.24; P = 0.04) compared with gilts fed the maintenance pre-mating diet. Collectively, these data suggest that a nutritional strategy that increases embryo survival is also associated with an increase in individual blastocyst cell number and reduced within-litter variability in blastocyst size.

Animal Nutritional Physiological Phenomena↗

PubMed1999

Micronutrients in fetal growth and development.

The roles that the different vitamins and minerals play in fetal growth and development are reviewed, primarily with respect to growth and differentiation in humans; but, as appropriate, data provided from animal and cellular studies are also considered.

Animals↗