Jennifer Dandrea

Peri-Implantation Undernutrition Programs Blunted Angiotensin II Evoked Baroreflex Responses in Young Adult Sheep

An adverse environment around conception and implantation influences later fetal growth and development to term in humans and sheep. Indeed, preimplantation undernutrition of rats elevated the systolic blood pressure of the resultant adult offspring. In this study, adult cardiovascular function is examined in a slower growing, non–litter-bearing species after peri-implantation undernutrition. Eight ewes were fed to 50% equivalent food intake of 12 control ewes from 1 to 30 days (term ≈147 days) only. Following consumption of an adequate diet to term, natural lambing, and then weaning, resting cardiovascular status and baroreflex function were examined in the resultant young adult offspring. Birth weight and postnatal growth to 1 year of age were unaffected by early undernutrition; however, nutrient-restricted sheep had increased pulse pressure, a reduced rate pressure product, and a leftward shift in their baroreflex function curve. Baroreflex sensitivity during angiotensin II infusion was also blunted in early nutrient-restricted sheep but the tachycardia following a reduction in central blood pressure appeared potentiated, relative to controls. The data suggest that peri-implantation undernutrition may program long-term cardiovascular dysfunction that ultimately increases the risk of hypertension later in life. An increase in regional angiotensin II activity during this critical early phase of development is a likely candidate mechanism for the effects observed. The data have broad implications for the health outcome of those offspring from mothers who were poorly nourished during early, often unknown pregnancy and for embryos artificially manipulated because of infertility treatment.

Influence of maternal pre-pregnancy body composition and diet during early-mid pregnancy on cardiovascular function and nephron number in juvenile sheep.

The prenatal diet can program an individuals cardiovascular system towards later higher resting blood pressure and kidney dysfunction, but the extent to which these programmed responses are directly determined by the timing of maternal nutritional manipulation is unknown. In the present study we examined whether maternal nutrient restriction targeted over the period of maximal placental growth, i.e. days 28-80 of gestation, resulted in altered blood pressure or kidney development in the juvenile offspring. This was undertaken in 6-month-old sheep born to mothers fed control (100-150 % of the recommended metabolisable energy (ME) intake for that stage of gestation) or nutrient-restricted (NR; 50 % ME; n 6) diets between days 28 and 80 of gestation. Controls were additionally grouped according to normal (>3, n 7) or low body condition score (LBCS; <2, n 6), thereby enabling us to examine the effect of maternal body composition on later cardiovascular function. From day 80 to term (approximately 147 d) all sheep were fed to 100 % ME. Offspring were weaned at 12 weeks and pasture-reared until 6 months of age when cardiovascular function was determined. Both LBCS and NR sheep tended to have lower resting systolic (control, 85 (se 2); LBCS, 77 (se 3); NR, 77 (se 3) mmHg) and diastolic blood pressure relative to controls. Total nephron count was markedly lower in both LBCS and NR relative to controls (LBCS, 59 (se 6); NR, 56 (se 12) %). Our data suggest that maternal body composition around conception is as important as the level of nutrient intake during early pregnancy in programming later cardiovascular health.

Effect of Maternal Nutrition on Brown Adipose Tissue and Its Prolactin Receptor Status in the Fetal Lamb

We investigated the influence of maternal nutritional enhancement during the second half of gestation on prolactin receptor (PRLR) abundance in fetal brown adipose tissue (BAT) and liver close to term (i.e. 141–144 d gestation). Ewes were provided with 100% (i.e. control;n = 8) or 150% (i.e. well-fed;n = 7) of their metabolic requirements from 80 to 144 d gestation. Crude plasma membranes were prepared from fetal BAT and hepatic tissue, and individual molecular weight isoforms for the long and short forms of the PRLR were detected by immunoblotting. Mitochondrial preparations were prepared from BAT to measure the amount of the BAT-specific mitochondrial uncoupling protein-1 and its thermogenic activity (i.e. guanosine 5′-diphosphate binding). Fetuses sampled from well-fed ewes were heavier (controls, 3927 ± 196 g; well-fed, 4783 ± 219 g;p = 0.01) but possessed less BAT per kilogram body weight (controls, 5.92 ± 0.43 g/kg; well-fed, 3.85 ± 0.19 g/kg;p = 0.001), which had a greater uncoupling protein-1 abundance (controls, 56 ± 5% of reference; well-fed, 78 ± 9% of reference;p < 0.01) and higher thermogenic activity (controls, 157 ± 41 pmol guanosine 5′-diphosphate per milligram mitochondrial protein; well-fed, 352 ± 36 pmol guanosine 5′-diphosphate per milligram mitochondrial protein;p < 0.01) than controls. Multiple isoforms of the long and short forms of the PRLR were detected in all tissues. BAT from well-fed fetuses had a higher abundance of the 15-kD isoform of the long form of the PRLR (controls, 1.6 ± 0.4 densitometric units; well-fed, 16.3 ± 2.0 densitometric units;p < 0.001). This isoform was not detected in hepatic tissue. Maternal nutrient intake had no effect on any other isoforms of the PRLR in BAT or liver. In conclusion, increasing the quantity of feed provided in late gestation acts to promote fetal weight and BAT maturation, the combination of which will enhance neonatal viability.

Ontogeny and nutritional programming of uncoupling protein-2 and glucocorticoid receptor mRNA in the ovine lung.

This study investigated the developmental and nutritional programming of uncoupling protein‐2 (UCP2), glucocorticoid receptor (GR) and 11β‐hydroxysteroid dehydrogenase type 1 (11βHSD1) mRNA in the sheep lung from the time of uterine attachment to 6 months of age. The effect of maternal nutrient restriction on lung development was determined in early to mid gestation (i.e. 28–80 days gestation, period of maximal placental growth, and embryonic and pseudoglandular stages of fetal lung development) and late gestation (i.e. 110–147 days gestation, period of maximal fetal growth, and canalicular and saccular stages of fetal lung development). Fetal lungs were sampled at 80 and 140 days (term ∼148 days) gestation, and sheep lungs at 1, 7, 30 days and 6 months. GR and 11βHSD1 mRNA were maximal at 140 days gestation, whereas UCP2 mRNA peaked at 1 day of age and then declined with postnatal age. Maternal nutrient restriction in both early‐to‐mid and late gestation had no effect on lung weight, but increased UCP2, GR and 11βHSD1 mRNA abundance at every sampling age. These findings suggest that the developmental ontogeny of UCP2 mRNA in the ovine lung is under local glucocorticoid hormone action and that maternal nutrient restriction has long‐term consequences for UCP2 and GR mRNA abundance in the lung irrespective of its timing.

Ambient Temperature, Maternal Dexamethasone, and Postnatal Ontogeny of Leptin in the Neonatal Lamb

The influence of route of delivery, ambient temperature, maternal dexamethasone treatment, and postnatal age on plasma concentrations of leptin or leptin mRNA abundance in perirenal adipose tissue was examined from 6-h-old lambs, born vaginally or delivered by cesarean section into warm (30°C) or cool (15°C) ambient temperatures, and from cesarean section–delivered lambs whose mothers had been treated with dexamethasone beginning 2 d before parturition. The ontogeny of leptin during the first month of postnatal life was also examined. In lambs born into a cool ambient temperature, but not in those born to dexamethasone-treated mothers, leptin mRNA abundance decreased within 6 h of birth. Plasma concentrations of leptin decreased during the first 6 h of life, an adaptation delayed by cesarean section birth. After the first day of postnatal life, both plasma concentrations of leptin and its mRNA increased to peak at 7 d of age and were positively correlated with each other, as well as with whole-body and perirenal adipose tissue weights. A similar relationship was not observed after 7 d of age, as plasma leptin declined despite an increase in adipose tissue weight. In conclusion, route of delivery, ambient temperature, or maternal dexamethasone therefore delays the rate of leptin disappearance after birth. Concomitantly, leptin abundance was only associated with body and adipose tissue weights for 1 week after birth, which may be coincident with the onset of peak lactation and the time at which nutrient supply should no longer be limiting to the neonate.

Differential Effects of Fetal Number and Maternal Nutrition in Late Gestation on Prolactin Receptor Abundance and Adipose Tissue Development in the Neonatal Lamb

The present study examined the extent to which abundance of the prolactin receptor (PRLR) and a range of primary mitochondrial proteins are influenced by either maternal nutrition and/or fetal number in adipose tissue. Pregnant sheep were control fed [consuming 100% of total metabolizable energy (ME) requirements (taking into account requirements for both ewe maintenance and growth of the conceptus to produce a 4.5-kg lamb at term) for that stage of gestation] or were nutrient restricted (consuming 60% of total ME requirements). All ewes lambed normally at term and both perirenal adipose and hepatic tissues were sampled within 6 h of birth. Plasma membranes and mitochondria were prepared and analyzed using immunoblotting for abundance of PRLR and/or cytochrome c, voltage-dependent anion channel (VDAC), and uncoupling protein-1 (UCP1). Irrespective of maternal nutrition, abundance of specific isoforms of PRLR were significantly higher in adipose tissue sampled from twins compared with singletons and total UCP1 concentration per milligram of tissue was increased (p < 0.05). There was no effect of fetal number on PRLR abundance in the liver. Maternal nutrient restriction resulted in an increased abundance of both cytochrome c (p < 0.001) and VDAC in adipose tissue of twins but not singletons. This occurred despite maternal nutrition having no effect on either lamb body or adipose tissue weights, although both were lower (p < 0.05) in twins compared with singletons. In conclusion, fetal adipose tissue development is highly sensitive to nutritionally mediated changes in late gestation. An increase in fetal number results in greater PRLR abundance, which, in conjunction with a decrease in maternal nutrition, results in up-regulation of specific mitochondrial proteins.

Maternal nutrient restriction during placental growth, programming of fetal adiposity and juvenile blood pressure control.

Epidemiological and experimental studies have demonstrated that maternal undernutrition during pregnancy is associated with abnormal placental growth. In sheep, maternal nutrient restriction over the period of rapid placental growth (30-80 days) restricts placentome growth. Then following adequate nutrition up to term (147 days), placental mass is greater in association with a higher total abundance of the predominant placental glucose transporter-1. The resulting lambs are larger at birth, have heavier kidneys with an increased expression of the glucocorticoid-responsive type 1 angiotensin II receptor. Near to term, these fetuses possess more adipose tissue, the endocrine sensitivity of which is markedly enhanced. For example, the abundance of mRNA for 11β-hydroxysteroid dehydrogenase type 1, which catalyses the conversion of cortisone to bio-active cortisol is increased. This is associated with a higher abundance of both leptin and glucocorticoid receptor mRNA. At 6 months of age, the juvenile offspring of nutrient restricted ewes have lower resting blood pressure that was positively correlated with plasma cortisol concentration, suggesting their blood pressure could be more strongly driven by circulating cortisol. These offspring also exhibited a greater pressor response to vasoconstrictor challenges, but showed no difference in vasodilatory response. At this age, the kidney weight was similar between groups, but the abundance of cytochrome c in kidney mitochondria was enhanced in lambs born to nutrient restricted ewes that could indicate increased mitochondrial activity. Reduced maternal nutrition during the period of rapid placental growth may therefore contribute to hypertension in later life through physiological and vascular adaptations during fetal life.