Microvascular rarefaction and decreased angiogenesis in rats with fetal programming of hypertension associated with exposure to a low-protein diet in utero

In hypertension, increased peripheral vascular resistance results from vascular dysfunction with or without structural changes (vessel wall remodeling and/or microvascular rarefaction). Humans with lower birth weight exhibit evidence of vascular dysfunction. The current studies were undertaken to investigate whether in utero programming of hypertension is associated with in vivo altered response and/or abnormal vascular structure. Offspring of Wistar dams fed a normal (CTRL) or low (LP)-protein diet during gestation were studied. Mean arterial blood pressure response to ANG II was significantly increased, and depressor response to sodium nitroprusside (SNP) infusions significantly decreased in male LP adult offspring relative to CTRL. No arterial remodeling was observed in male LP compared with CTRL offspring. Capillary and arteriolar density was significantly decreased in striated muscles from LP offspring at 7 and 28 days of life but was not different in late fetal life [day 21 of gestation (E21)]. Angiogenic potential of aortic rings from LP newborn (day of birth, P0) was significantly decreased. Striated muscle expressions (Western blots) of ANG II AT(1) receptor subtype, endothelial nitric oxide synthase, angiopoietin 1 and 2, Tie 2 receptor, vascular endothelial growth factor and receptor, and platelet-derived growth factor C at E21 and P7 were unaltered by antenatal diet exposure. In conclusion, blood pressure responses to ANG II and SNP are altered, and microvascular structural changes prevail in this model of fetal programming of hypertension. The capillary rarefaction is absent in the fetus and appears in the neonatal period, in association with decreased angiogenic potential. The study suggests that intrauterine protein restriction increases susceptibility to postnatal factors resulting in microvascular rarefaction, which could represent a primary event in the genesis of hypertension.

The Canadian Partnership for Tomorrow Project: a pan-Canadian platform for research on chronic disease prevention

BACKGROUND

Understanding the complex interaction of risk factors that increase the likelihood of developing common diseases is challenging. The Canadian Partnership for Tomorrow Project (CPTP) is a prospective cohort study created as a population-health research platform for assessing the effect of genetics, behaviour, family health history and environment (among other factors) on chronic diseases.

METHODS

Volunteer participants were recruited from the general Canadian population for a confederation of 5 regional cohorts. Participants were enrolled in the study and core information obtained using 2 approaches: attendance at a study assessment centre for all study measures (questionnaire, venous blood sample and physical measurements) or completion of the core questionnaire (online or paper), with later collection of other study measures where possible. Physical measurements included height, weight, percentage body fat and blood pressure. Participants consented to passive follow-up through linkage with administrative health databases and active follow-up through recontact. All participant data across the 5 regional cohorts were harmonized.

RESULTS

A total of 307 017 participants aged 30-74 from 8 provinces were recruited. More than half provided a venous blood sample and/or other biological sample, and 33% completed physical measurements. A total of 709 harmonized variables were created; almost 25% are available for all participants and 60% for at least 220 000 participants.

INTERPRETATION

Primary recruitment for the CPTP is complete, and data and biosamples are available to Canadian and international researchers through a data-access process. The CPTP will support research into how modifiable risk factors, genetics and the environment interact to affect the development of cancer and other chronic diseases, ultimately contributing evidence to reduce the global burden of chronic disease.

Maternal and fetal leptin, adiponectin levels and associations with fetal insulin sensitivity

OBJECTIVE

It remains uncertain whether leptin and adiponectin levels are correlated in maternal vs. fetal circulations. Little is known about whether leptin and adiponectin affect insulin sensitivity during fetal life.

DESIGN AND METHODS

In a prospective singleton pregnancy cohort (n = 248), we investigated leptin and adiponectin concentrations in maternal (at 24-28 and 32-35 weeks of gestation) and fetal circulations, and their associations with fetal insulin sensitivity (glucose/insulin ratio, proinsulin level).

RESULTS

Comparing concentrations in cord vs. maternal blood, leptin levels were 50% lower, but adiponectin levels more than doubled. Adjusting for gestational age at blood sampling, consistent and similar positive correlations (correlation coefficients: 0.31-0.34, all P < 0.0001) were observed in leptin or adiponectin levels in maternal (at 24-28 or 32-25 weeks of gestation) vs. fetal circulations. For each SD increase in maternal plasma concentration at 24-28 weeks, cord plasma concentration increased by 12.7 (95% confidence interval 6.8-18.5) ng/ml for leptin, and 2.9 (1.8-4.0) µg/ml for adiponectin, respectively (adjusted P < 0.0001). Fetal insulin sensitivity was negatively associated with cord blood leptin (each SD increase was associated with a 5.4 (2.1-8.7) mg/dl/µU/ml reduction in cord plasma glucose/insulin ratio, and a 5.6 (3.9, 7.4) pmol/l increase in proinsulin level, all adjusted P < 0.01) but not adiponectin (P > 0.4) levels). Similar associations were observed in nondiabetic full-term pregnancies (n = 211).

CONCLUSIONS

The results consistently suggest a maternal impact on fetal leptin and adiponectin levels, which may be an early life pathway in maternal-fetal transmission of the propensity to obesity and insulin resistance.

Effect of cortisol on gene expression of the renin-angiotensin system in fetal sheep

Components of the renin-angiotensin system have been found in a variety of tissues during fetal and postnatal life and appear to be developmentally regulated. We postulated that hormonal changes associated with parturition participate in the regulation of renin, angiotensinogen (Ao) and angiotensin type 1 receptor (AT1) gene expression. Cortisol, which increases rapidly in fetal blood before delivery, has been shown to influence the maturation of various systems in the developing fetus. To test the hypothesis that an increase in cortisol regulates fetal renin. Ao, and AT1 mRNA gene expression, we used Northern blot analysis to study the effects of an intraperitoneal infusion of cortisol (3 mg/h, 1 mL/h) for 48 h on the expression of these genes in twin ovine fetuses (n = 10 pairs) at 130-d gestation (term 145 d); one twin in each pair served as a saline-treated control (0.9% NaCl, 1 mL/h). Plasma cortisol levels were significantly higher in cortisol-treated fetuses (113 +/- 23 nmol/dL) than in twin controls (4.6 +/- 0.8 nmol/dL). Cortisol infusion significantly decreased AT1 receptor mRNA levels in kidney and liver by 24 +/- 7% and 27 +/- 8%, respectively, when compared with controls (p < 0.05), whereas in contrast, increased mRNA levels (p < 0.05) in heart right atrium (91 +/- 23%) and ventricle (59 +/- 20%). Renin mRNA levels decreased in renal cortex by 77 +/- 13% (p < 0.05) in cortisol-treated animals compared with controls. Hepatic Ao mRNA levels decreased by 15 +/- 5% in response to cortisol (p < 0.05), whereas no significant effect was seen on renal Ao gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal and fetal IGF-I and IGF-II levels, fetal growth, and gestational diabetes

CONTEXT

It remains uncertain whether maternal IGF-I is associated with fetal growth. Little is known about the role of maternal IGF-II in fetal growth and whether IGF-I or IGF-II is implicated in fetal hypertrophy in gestational diabetes.

OBJECTIVE

The objective of the study was to assess maternal and fetal IGF-I and IGF-II levels in association with fetal growth and gestational diabetes. STUDY DESIGN, POPULATION, AND OUTCOMES: A singleton pregnancy cohort study (n = 307). The primary outcome was birth weight.

RESULTS

Maternal plasma concentrations increased by an average of 55.4% for IGF-I and 11.8% for IGF-II between 24-28 and 32-35 weeks of gestation. The maternal IGF-I but not IGF-II level was correlated with birth weight and placental weight. Adjusting for maternal and infant characteristics, each SD increase in maternal IGF-I level at 24-28 weeks was associated with a 75-g (95% confidence intervals 29-120) increase in birth weight, a 20-g (7-33) increase in placental weight, and a 1.91-fold (1.28-2.86) higher odds of macrosomia (birth weight > 90th percentile). Similar associations were observed for the maternal IGF-I level at 32-35 weeks. Maternal and fetal IGF-I (but not IGF-II) levels were significantly higher in gestational diabetic than in nondiabetic pregnancies. The significantly higher birth weight z scores in diabetic pregnancies disappeared after adjusting for maternal and fetal IGF-I levels alone.

CONCLUSIONS

Higher maternal IGF-I (but not IGF-II) levels at mid- and late gestation may indicate greater placental and fetal growth. IGF-I (but not IGF-II) may be implicated in fetal hypertrophy in gestational diabetes.

Differential gene expression and regulation of renal angiotensin II receptor subtypes (AT1 and AT2) during fetal life in sheep

Previous studies have shown that angiotensin II subtype 2 (AT2) receptors appear early during renal embryonic development. Factors involved in the regulation of AT2 receptors during renal development, however, have not been investigated. The present study was designed 1) to characterize the ontogeny of renal AT2 gene expression during the last half of gestation in fetal sheep and newborn lambs, 2) to compare changes in AT1 and AT2 gene expression during renal development, 3) to determine the influence of AII in modulating renal AT1 and AT2 gene expression during fetal life, and 4) to characterize the role of cortisol in modulating renal AT2 gene expression during the last trimester of gestation in fetal sheep. To perform these studies, we first isolated and cloned a polymerase chain reaction product that has 92 and 90% homology with the cDNA encoding the human and rat AT2 receptors, respectively. Using this sheep AT2 cDNA probe, we demonstrated that the sheep AT2 gene was encoded in a single locus. In addition, we showed that renal AT2 mRNA expression was high early during fetal life (60-90-d gestation) and decreased rapidly thereafter. In contrast, the expression of renal AT1 receptor gene was low at 60-d gestation and increased during the last trimester of gestation. We found that a continuous i.v. infusion (1 mL/h) of AII (9.5 mM/n) for 24 h, which raised plasma AII levels from 84 +/- 9 pg/mL to 210 +/- 21 pg/mL, decreased the expression of both renal AT1 and AT2 genes in third trimester fetal sheep. On the other hand, we observed that cortisol, known to decrease AT1 gene expression in the fetus, had no effect on AT2 gene expression. In summary, this study demonstrates that AII, but not glucocorticoids, contributes to the regulation of renal AT2 gene expression during development and that there is differential regulation of AT1 and AT2 receptors.

Maternal glucose tolerance in pregnancy affects fetal insulin sensitivity

OBJECTIVE

Offspring of mothers with impaired glucose tolerance are far more likely to develop type 2 diabetes. We tested the hypothesis that maternal glucose tolerance in pregnancy affects fetal insulin sensitivity or beta-cell function.

RESEARCH DESIGN AND METHODS

In a prospective singleton pregnancy cohort study, we analyzed glucose, insulin, and proinsulin concentrations in maternal blood at the 50-g oral glucose tolerance test (OGTT) at 24-28 weeks of gestation and in venous cord blood (n = 248). The cord blood glucose-to-insulin ratio and proinsulin concentration were used as indicators of fetal insulin sensitivity and the proinsulin-to-insulin ratio was used as an indicator of fetal beta-cell function.

RESULTS

Higher OGTT blood glucose levels were associated with significantly lower cord plasma glucose-to-insulin ratios (r = -0.31, P < 0.001) and higher proinsulin concentrations (r = 0.31, P < 0.001) but not with proinsulin-to-insulin ratios. In a comparison of gestational diabetic (n = 26) versus euglycemic pregnancy, cord blood glucose-to-insulin ratios were substantially lower (geometric mean 10.1 vs. 20.0 mg/dl/microU/ml; P < 0.001), whereas proinsulin concentrations were much higher (24.4 vs. 13.8 pmol/l; P < 0.001), despite similar cord blood glucose concentrations indicating adequate management of diabetes. The differences remained significant after controlling for prepregnancy and fetal adiposity, family history of diabetes, gestational age, and other potential confounders. Significant changes in the glucose-to-insulin ratio and proinsulin concentration were also observed in obese (n = 31) mothers, but the differences became not statistically significant after adjustment for maternal glucose tolerance and fetal adiposity.

CONCLUSIONS

Maternal glucose intolerance may impair fetal insulin sensitivity (but not beta-cell function) and consequently "program" the susceptibility to type 2 diabetes.

Exaggerated vasomotor response to ANG II in rats with fetal programming of hypertension associated with exposure to a low-protein diet during gestation

The renin-angiotensin system plays a key role in the initiation and maintenance of elevated blood pressure associated with altered intrauterine milieu. The current studies were undertaken to verify whether vascular response to ANG II is increased in adult offspring of low-protein fed dams (LP) compared with control (CTRL) and if so, to examine underlying mechanism(s). ANG II-induced contraction of carotid rings was increased in LP (Emax, the maximum asymptote of the curve, relative to maximal response to KCl 80 mM: 230 ± 3% LP vs. 201 ± 2% CTRL, P < 0.05). In both groups, contraction to ANG II was mediated solely by AT1R. Responses to thromboxane A2 analog U-46619 and to KCl 80 mM under step increases in tension were similar between groups. Endothelium depletion enhanced contraction to ANG II in both groups, more so in LP. Blockade of endothelin formation had no effect on response to ANG II, and ANG-(1–7) did not elicit vasomotor response in either group. Superoxide dismutase (SOD) analog Tempol normalized LP without modifying CTRL response to ANG II. Basal levels of superoxide (aortic segments, lucigenin-enhanced chemiluminescence and fluorescent dye hydroethidine) were higher in LP. ANG II further increased superoxide production in LP only, and this was inhibited by coincubation with diphenylene iodonium or apocynin (inhibitor of NADPH oxidase complex). AT1R expression in carotid arteries was increased in LP, whereas SOD expression was unchanged. In conclusion, vasoconstriction to ANG II is exaggerated in this model of developmental programming of hypertension, secondary to enhanced vascular production of superoxide anion by NADPH oxidase with concomitant increase of AT1R expression.

Mechanisms of developmental programming of the metabolic syndrome and related disorders

There is consistent epidemiological evidence linking low birth weight, preterm birth and adverse fetal growth to an elevated risk of the metabolic syndrome (obesity, raised blood pressure, raised serum triglycerides, lowered serum high-density lipoprotein cholesterol and impaired glucose tolerance or insulin resistance) and related disorders. This “fetal or developmental origins/programming of disease” concept is now well accepted but the “programming” mechanisms remain poorly understood. We reviewed the major evidence, implications and limitations of current hypotheses in interpreting developmental programming and discuss future research directions. Major current hypotheses to interpret developmental programming include: (1) thrifty phenotype; (2) postnatal accelerated or catch-up growth; (3) glucocorticoid effects; (4) epigenetic changes; (5) oxidative stress; (6) prenatal hypoxia; (7) placental dysfunction; and (8) reduced stem cell number. Some hypothetical mechanisms (2, 4 and 8) could be driven by other upstream “driver” mechanisms. There is a lack of animal studies addressing multiple mechanisms simultaneously and a lack of strong evidence linking clinical outcomes to biomarkers of the proposed programming mechanisms in humans. There are needs for (1) experimental studies addressing multiple hypothetical mechanisms simultaneously; and (2) prospective pregnancy cohort studies linking biomarkers of the proposed mechanisms to clinical outcomes or surrogate biomarker endpoints. A better understanding of the programming mechanisms is a prerequisite for developing early life interventions to arrest the increasing epidemic of the metabolic syndrome, type 2 diabetes and other related disorders.

Nitric oxide in retinal and choroidal blood flow autoregulation in newborn pigs: interactions with prostaglandins

The role of nitric oxide (NO) as well as its interaction with prostaglandins (PG) in setting the limits of autoregulation of retinal blood flow (RBF) and choroidal blood flow (ChBF) were studied in newborn pigs (1-5 d old). Blood flows were measured by the microsphere technique. Low and high ocular perfusion pressures (OPP) were induced by inflating balloon-tipped catheters placed at the aortic root and isthmus, respectively. Animals were treated with the NO synthase inhibitors, NG-nitro-L-arginine methyl ester (L-NAME, 1 mg/kg followed by 50 mu g/kg/min; n = 12) or NG-monomethyl-L-arginine (L-NMMA, same dose as L-NAME; n = 3), or with saline (n = 12). In separate animals (n = 42), guanosine 3',5'-cyclic monophosphate (cGMP), the second messenger for NO, and PG were measured at an average OPP of 90 mm Hg and 125 +/- 6 mm Hg; cGMP levels served as an index of NO release. The effect of the NO donor sodium nitroprusside on choroidal vessel diameter was determined using video imaging of isolated eyecup preparations. In control animals RBF was constant only within a range of 30 to 80 mm Hg OPP (r = 0.03, p > 0.9). There was no autoregulation of ChBF which increased as a function of OPP (tau = 0.58-0.72, p < 0.01). L-NAME and L-NMMA prevented a change in RBF and ChBF from 30 to 146 mm Hg [the highest OPP studied (r < 0.3, p > 0.15)] and caused an increase in retinal as well as choroidal vascular resistance as OPP was raised; these agents did not affect ocular blood flow at OPP < 30 mm Hg. Elevated OPP caused increases in cGMP, 6-keto-PGF1alpha, and PGE2 in the choroid (a vascular tissue), which were prevented by L-NAME and L-NMMA. Sodium nitroprusside caused a dilatation of choroidal vessels in isolated eyecup preparations, which was significantly attenuated by indomethacin. Data suggest a role for NO in the autoregulation of RBF and ChBF in the newborn such that a release of NO during a rise in OPP prevents adequate constriction necessary for maintaining RBF and ChBF constant; data also suggest that the vasodilator effect of NO might in part be mediated through a release of PG.

Impact of fetal programming, birth weight, and infant feeding on later hypertension

The concept of developmental origins of adult disease derives from both epidemiologic and basic sciences. This brief review considers the impact of the intrauterine milieu, intrauterine growth retardation, premature birth, and infant feeding on later hypertension and kidney disease.

Female fetus is associated with greater maternal insulin resistance in pregnancy

AIM

To explore the hypothesis that female fetus is associated with greater maternal insulin resistance during pregnancy.

METHODS

In a singleton pregnancy cohort study (n = 299), we compared maternal insulin resistance according to fetal sex, based on plasma biomarkers from a 50-g 1-h oral glucose tolerance test at 24-28 weeks gestation. The primary outcome was plasma glucose-to-insulin ratio. Other outcomes included plasma proinsulin-to-insulin ratio, and insulin, proinsulin, leptin, adiponectin and insulin-like growth factor I and II concentrations.

RESULTS

After adjusting for maternal race, age, parity, education, pre-pregnancy BMI, smoking and alcohol use, history of gestational diabetes, and gestational age at blood sampling, plasma insulin concentrations were significantly higher (mean ± sd: 66.4 ± 50.5 vs. 51.0 ± 46.1 mU/l; adjusted P = 0.001), and glucose-to-insulin ratios significantly lower (2.60 ± 2.03 vs. 3.77 ± 4.98 mg/dl/mU/l; adjusted P = 0.002) in women bearing a female vs those bearing a male fetus, despite similar glucose levels (116.4 ± 27.2 vs. 117.0 ± 31.9 mg/dl; adjusted P = 0.92).There were no significant differences in proinsulin-to-insulin ratios, or leptin, adiponectin, insulin-like growth factor I and insulin-like growth factor II concentrations by fetal sex.

CONCLUSION

Female fetus may be associated with greater maternal insulin resistance during pregnancy.

Effect of antenatal glucocorticoids on sympathetic nerve activity at birth in preterm sheep

Renal sympathetic nerve activity (RSNA) increases rapidly after delivery of term fetal sheep and parallels the rise in heart rate (HR) and arterial pressure. To examine the RSNA response at birth in immature lambs, experiments were performed in chronically instrumented preterm fetal sheep (118- to 125-day gestation, term 145 days) before and after delivery by cesarean section. HR remained unchanged from fetal values at 1 and 4 h after birth, whereas mean arterial blood pressure (MABP) decreased significantly (P < 0.05) by 4 h after delivery. RSNA significantly decreased after premature birth in all animals studied (n = 6), achieving only 39 +/- 17% of fetal RSNA (P < 0.05; all results are mean +/- SE). Because cardiovascular function after premature birth is improved by the use of antenatal corticosteroids, we also tested the hypothesis that corticosteroid administration would evoke a more pronounced sympathetic response in prematurely delivered lambs (n = 7, 118- to 125-day gestation). After maternal administration of dexamethasone (5 mg i.m., 48 and 24 h before delivery), RSNA increased after birth in six of seven fetuses to 166 +/- 32% of the fetal RSNA value. Dexamethasone treatment also decreased the sensitivity of baroreflex-mediated changes in HR in response to increases in MABP. Because the sympathetic response at birth is depressed in preterm compared with term lambs, we performed an additional study (n = 8) to determine if immature sheep are capable of mounting a sympathetic response to cold. In utero cooling produced rapid and sustained increases in MABP (20 +/- 4%), HR (26 +/- 6%), and RSNA (282 +/- 72%) (all P < 0.05), consistent with a generalized sympathoexcitation. These results suggest that sympathoexcitation is absent after premature delivery despite the presence of functional descending autonomic pathways. Furthermore, exogenous corticosteroids appear to have a maturational effect on the sympathetic response at birth, which may be one mechanism by which maternal steroid administration improves postnatal cardiovascular homeostasis.

Longitudinal circulating concentrations of long-chain polyunsaturated fatty acids in the third trimester of pregnancy in gestational diabetes

AIM

Gestational diabetes mellitus is a common complication of pregnancy. Long-chain polyunsaturated fatty acids (LCPUFA) are essential for fetal neurodevelopment. Docosahexaenoic acid (DHA) is the predominant n-3 LCPUFA in the brain and retina. Circulating absolute concentrations of total n-3 and n-6 LCPUFAs rise during normal pregnancy. It remains unclear whether gestational diabetes may affect the normal rise in circulating concentrations of LCPUFAs in the third trimester of pregnancy - a period of rapid fetal neurodevelopment. This study aimed to address this question.

METHODS

In a prospective singleton pregnancy cohort, fatty acids in fasting plasma total lipids were measured at 24-28 and 32-35 weeks of gestation in women with (n = 24) and without gestational diabetes mellitus (n = 116). Fatty acid desaturase activity indices were estimated by relevant product-to-precursor fatty acid ratios. Dietary nutrient intakes were estimated by a food frequency questionnaire.

RESULTS

Plasma absolute concentrations of total n-6 LCPUFAs rose significantly between 24-28 and 32-35 weeks of gestation in women with or without gestational diabetes, whereas total n-3 LCPUFAs and DHA concentrations rose significantly only in women without gestational diabetes (all P < 0.01). Delta-5 desaturase indices (20:4n-6/20:3n-6) were similar, but delta-6 desaturase indices (18:3n-6/18:2n-6) were significantly lower in women with gestational diabetes at 32-35 weeks of gestation. Dietary intakes of all fatty acids were comparable.

CONCLUSION

The normal rise in circulating absolute concentrations of DHA and total n-3 LCPUFAs in the third trimester of pregnancy may be compromised in gestational diabetes, probably due to impaired synthesis or mobilization rather than dietary intake difference.

Ontogeny of angiotensin II type 1 receptor mRNAs in fetal and neonatal rat brain

Studies have demonstrated a specific function of the angiotensin II (Ang II) type 1 receptor (AT(1)) in regulation of adult central cardiovascular, fluid, and pituitary hormone release and a predominant role of the renin-angiotensin system in fetal and neonatal cardiovascular homeostasis. The pattern of brain AT(1) mRNA expression during fetal and neonatal development is currently unknown. We used radiolabeled cRNA probes for in situ hybridization histochemistry to determine the ontogenic development of the two AT(1) subtypes (AT(1a) and AT(1b)) mRNA in rat brain, from 11 days of gestation (E11) to 28 days after birth (P28). No AT(1b) mRNA was detected in the developing brain, whereas AT(1a) mRNA was first detected at E19. The age at which AT(1a) mRNA is first detected varied among different brain areas and expression predominates in areas involved in fluid homeostasis, pituitary hormone release, and cardiovascular regulation, where it persists until P28. AT(1a) mRNA expression is present from E19 onward in the median preoptic nucleus, the vascular organ of the lamina terminalis, the paraventricular nucleus, the periaqueductal gray, the nucleus raphe pallidus, the motor facial nucleus, and very weakly in the nucleus of the solitary tract and the ambiguous nucleus, and at E21 in the subfornical organ, the anterior olfactory nucleus and the piriform cortex. AT(1a) mRNA expression is present after birth in many regions, including the preoptic and lateral hypothalamic areas, the area postrema and medullary reticular nuclei. In conclusion, during brain development, expression of AT(1a) mRNA, appears in late gestation at E19, predominantly in forebrain areas involved in fluid homeostasis and cardiovascular regulation. In contrast, AT(1a) mRNA expression is absent or present only in very small amounts until after birth in many medullary nuclei, known to play an important role in cardiovascular modulation. Our results suggest that, in perinatal life, AT(1a) is involved in fluid and perhaps cardiovascular homeostasis and that the role of Ang II in modulating medullary cardiovascular centers matures later in postnatal life.

Identification of endocrine cell populations expressing the AT1B subtype of angiotensin II receptors in the anterior pituitary

Angiotensin II (Ang II) participates in the regulation of anterior pituitary hormone secretion by acting either directly on the anterior pituitary or indirectly on the hypothalamus. When applied directly on pituitary cells, Ang II increases both ACTH and PRL secretion and has also been reported to affect GH secretion. Three distinct subtypes of Ang II receptors (AT1A, AT1B, and AT2) have been identified; they are unequally distributed and differently regulated in various tissues. We have previously demonstrated that only AT1A receptors are present in the hypothalamus while anterior pituitary cells express predominantly the AT1B subtype. Using in situ hybridization in combination with immunohistochemistry, the aim of the present study was to identify the phenotype of the endocrine cell expressing AT1B receptor messenger RNA (mRNA) in the anterior pituitary of adult male Sprague-Dawley rats. Expression of AT1B receptor mRNA was present in 33.9 +/- 1.0% of anterior pituitary cells. AT1B mRNA is predominantly expressed by lactotropes (78.2 +/- 2.1% of AT1B mRNA-expressing cells) and to a lower degree by corticotropes (18.3 +/- 2.1%) and is not detectable in somatotropes, mammosomatotropes, gonadotropes, or thyrotropes. These results indicate that in adult male rats, Ang II, which has been shown to be synthesized in gonadotropes, can directly stimulate PRL and ACTH release from lactotropes and corticotropes through activation of AT1B receptors. As only 53.8 +/- 2.7% of lactotropes and 23.6 +/- 2.8% of corticotropes expressed AT1B mRNA, our findings suggest a functional heterogeneity of both cell types regarding their sensitivity to Ang II.

Cancer risk in children and young adults born preterm: A systematic review and meta-analysis

Introduction

Risk of developing a malignancy when born premature is unknown. We hypothesised that risk of certain cancers might be increased in youth born preterm versus term. We therefore performed a systematic review and meta-analysis to evaluate the incidence of malignancy in the context of preterm birth, according to various cancer types.

Methods

The study was designed per MOOSE and PRISMA guidelines. Articles were identified through November 2015. Observational studies exploring the association between childhood malignancy and birth characteristics were included. Of the 1658 records identified, 109 full text articles were evaluated for eligibility. Random effects meta-analyses were conducted on 10/26 studies retained; 95% confidence intervals were computed and adjusted following sensitivity analysis. Publication bias was evaluated using funnel plots, Begg’s and Egger’s tests.

Results

No differences in risk of primary central nervous system tumor [OR 1.05; 95% CI 0.93–1.17, 5 studies, 580 cases] and neuroblastoma [OR 1.09; 95% CI 0.90–1.32, 5 studies, 211 cases] were observed in individuals born <37 versus ≥37 weeks’ gestation. Preterm birth was consistently associated with hepatoblastoma [ORs 3.12 (95% CI 2.32–4.20), 1.52 (95% CI 1.1–2.1), 1.82 (95% CI 1.01–3.26), and 2.65 (95% CI 1.98–3.55)], but not leukemia, astrocytoma, ependymoma, medulloblastoma, lymphoma, nephroblastoma, rhabdomyosarcoma, retinoblastoma or thyroid cancer.

Conclusions

Children born premature may be at increased risk for hepatoblastoma but there is no strong evidence of an increased risk of primary central nervous system tumours or neuroblastoma. There is insufficient evidence to conclude whether prematurity modulates the risk of other childhood cancers.

Autonomic adjustments to severe hypotension in fetal and neonatal sheep

In fetal sheep, severe hypotension causes heart rate (HR) slowing. Studies during development have also shown that a reflex bradycardia and hypotension can be elicited after chemostimulation with veratridine and is dependent on the age of the animal. In adults, a vagally mediated depressor reflex characterized by bradycardia, hypotension, and withdrawal of efferent sympathetic activity can be observed after stimulation of chemosensitive or mechanosensitive cardiac receptors with veratridine or in circumstances of reduced cardiac filling. This reflex, known as the Bezold-Jarisch reflex, plays a role in disease states such as myocardial ischemia and hemorrhage. The objectives of our study were to determine whether a sympathoinhibitor depressor reflex, along with the bradycardia, is observed during pharmacologically induced hypotension in fetal and newborn lambs. In both fetal and newborn lambs, HR and renal sympathetic nerve activity (RSNA) initially increased (p < 0.05) in response to nitroprusside infusion to reach a maximum value. The range (or "plateau") of mean arterial blood pressure over which maximum RSNA was maintained constant before withdrawal of sympathetic tone started to be observed was significantly (p < 0.05) smaller in fetuses (0.3 +/- 0.3 mm Hg) than newborn (6 +/- 1 mm Hg) lambs. Similarly, the plateau over which maximum HR was maintained before onset of bradycardia was significantly smaller in fetuses (4 +/- 1 versus 11 +/- 2 mm Hg). The mean arterial blood pressure level ("threshold") at which a depressor reflex was triggered was significantly (p < 0.05) lower in fetal than newborn sheep (35 +/- 2 versus 53 +/- 3 mm Hg for HR and 35 +/- 2 versus 57 +/- 2 mm Hg for RSNA). The rates of fall (slopes) for both HR and RSNA were also significantly (p < 0.05) more pronounced in fetuses (1.85 +/- 0.27 and 6.08 +/- 2.45%/mm Hg) than in newborns (1.21 +/- 0.16 and 1.97 +/- 0.32%/mm Hg). Bilateral vagotomy significantly increased the plateau of mean arterial blood pressure over which maximum RSNA and HR were maintained constant. Vagotomy also decreased the threshold for both RSNA and HR and the slope of the RSNA response to the nitroprusside infusion in newborn lambs. Results from this study show that activation of the arterial baroreflex during nitroprusside-induced hypotension is followed by withdrawal of sympathetic tone and bradycardia and that this depressor reflex is more pronounced in late-gestation fetuses than newborn lambs and is significantly attenuated after bilateral vagotomy in newborn lambs.

Major role for neuronal NO synthase in curtailing choroidal blood flow autoregulation in newborn pig

We examined whether nitric oxide (NO) generated from neuronal NO synthase (nNOS) contributes to the reduced ability of the newborn to autoregulate retinal blood flow (RBF) and choroidal blood flow (ChBF) during acute rises in perfusion pressure. In newborn pigs (1-2 days old), RBF (measured by microsphere) is autoregulated over a narrow range of perfusion pressure, whereas ChBF is not autoregulated. N(G)-nitro-L-arginine methyl ester (L-NAME) or specific nNOS inhibitors 7-nitroindazole, 3-bromo-7-nitroindazole, and 1-(2-trifluoromethyl-phenyl)imidazole as well as ganglionic blocker hexamethonium, unveiled a ChBF autoregulation as observed in juvenile (4- to 6-wk old) animals, whereas autoregulation of RBF in the newborn was only enhanced by L-NAME. All NOS inhibitors and hexamethonium prevented the hypertension-induced increase in NO mediator cGMP in the choroid. nNOS mRNA expression and activity were three- to fourfold higher in the choroid of newborn pigs than in tissues of juvenile pigs. It is concluded that increased production of NO from nNOS curtails ChBF autoregulation in the newborn and suggests a role for the autonomic nervous system in this important hemodynamic function, whereas, for RBF autoregulation, endothelial NOS seems to exert a more important contribution in limiting autoregulation.

Long-term impact of an antioxidant-deficient neonatal diet on lipid and glucose metabolism

Newborn infants are at risk for oxidative stress leading to metabolic syndrome features. Oxidative stress can be induced by oxidant load such as oxygen supplementation, peroxides from intravenous nutrition, or low antioxidant defenses. We hypothesize that a modulation of antioxidant defenses during the neonatal period, without external oxidant challenge, will have a long-term influence on energy metabolism. Guinea pigs were fed between their third and their seventh day of life a regular chow leading to "mature" antioxidant defenses or a deficient chow leading to lower antioxidant defenses. Between weeks 1 and 14, the animals were fed regular chow. The hepatic oxidized redox status of glutathione associated with the deficient diet (-221 +/- 2 vs -228 +/- 1 mV, p < 0.01) was maintained until 14 weeks. At 13-14 weeks, animals fed the deficient diet presented lower plasma TG (479 +/- 57 vs 853 +/- 32 microM, p < 0.01), lower blood glucose (5.8 +/- 0.3 vs 6.9 +/- 0.3 mM, p < 0.05), and better tolerance to glucose (p < 0.05). Blood glucose correlated negatively with the redox status (r2 = 0.47, p < 0.01). Low antioxidant defenses during the neonatal period induce a better energy substrate profile associated with an oxidized redox status later in life. These findings suggest being aware of negative consequences when adopting "aggressive" antioxidant therapies in newborn infants.

Neonatal exposure to oxidants induces later in life a metabolic response associated to a phenotype of energy deficiency in an animal model of total parenteral nutrition

Failure to protect total parenteral nutrition (TPN) from ambient light exacerbates the generation of peroxides, which affects blood glucose and plasma triacylglyceride (TG) in neonates. Based on the concept that the origin of adult diseases can be traced back to perinatal life, it was hypothesized that neonatal exposure to peroxides may affect energy availability later in life. Three-day-old guinea pigs, fitted with a jugular catheter, were fed regular chow (sham) +/- i.v. 350 microM H2O2 (sham + H2O2) or nourished with light-protected TPN [TPN(-)L, 209 +/- 9 microM peroxides] or light-exposed TPN [TPN(+)L, 365 +/- 15 microM peroxides]. After 4 d, infusions were stopped and animals fed chow. Spontaneous ambulatory movements, fasting blood glucose, glucose tolerance, TG, hepatic activities of glucokinase, phosphofructokinase (key enzymes of glycolysis), and acetyl-CoA carboxylase (key enzymes of lipogenesis) were determined at 12-14 wk and compared by ANOVA (p < 0.05). Relative to sham, the animals from sham + H2O2, TPN(-)L and TPN(+)L groups had lower plasma TG explained for 36% by low phosphofructokinase activity; they had lower glucose tolerance, lower body weight, and lower physical activity. In conclusion, neonatal exposure to oxidant molecules such as peroxides has important consequences later in life on lipid and glucose metabolism leading to a phenotype of energy deficiency.

Developmentally increased cerebrovascular NO in newborn pigs curtails cerebral blood flow autoregulation

We tested the hypothesis that a reduced ability of the newborn (1-2 d old) to autoregulate cerebral blood flow (CBF) during acute hypertension is contributed by an increased synthesis of nitric oxide (NO) from endothelial (e) and neuronal NO synthase (nNOS). As previously reported, CBF (measured by radiolabeled microsphere technique) in newborn pigs remained constant only between 50 and 90 mm Hg of mean arterial blood pressure. Treatment of newborn pigs with Nomega-monomethyl-L-arginine or specific nNOS inhibitors 7-nitroindazole monosodium, 3-bromo-7-nitroindazole, and 1-(2-trifluoromethylphenyl) imidazole extended the upper limit of CBF autoregulation as seen in saline-treated (control) juvenile (4-6-wk-old) animals. Cerebrovascular production of nitrite (stable NO oxidation product) in vivo was markedly increased during hypertension (mean arterial blood pressure > 90 mm Hg) in newborn but not in the juvenile pigs. Inhibition of NOS with Nomega-monomethyl-L-arginine, 7-nitroindazole monosodium, 3-bromo-7-nitroindazole, or 1-(2-trifluoromethylphenyl) imidazole prevented the hypertension-induced increase in nitrite levels. In addition, eNOS and nNOS protein expression and activity were 2- to 3-fold higher (p < 0.05) in the cerebral microvasculature of newborn than in the tissues of juvenile pigs. It is concluded that during acute hypertension, excess production of NO associated with increased activity of NOS curtails the upper limit of CBF autoregulation in the newborn subject; in addition, nNOS seems to serve a significant role in this important physiologic function.

Contribution of birth weight to mental health, cognitive and socioeconomic outcomes: two-sample Mendelian randomisation

BACKGROUND

Low birth weight is associated with adult mental health, cognitive and socioeconomic problems. However, the causal nature of these associations remains difficult to establish owing to confounding.

AIMS

To estimate the contribution of birth weight to adult mental health, cognitive and socioeconomic outcomes using two-sample Mendelian randomisation, an instrumental variable approach strengthening causal inference.

METHOD

We used 48 independent single-nucleotide polymorphisms as genetic instruments for birth weight (genome-wide association studies' total sample: n = 264 498) and considered mental health (attention-deficit hyperactivity disorder (ADHD), autism spectrum disorder, bipolar disorder, major depressive disorder, obsessive-compulsive disorder, post-traumatic stress disorder (PTSD), schizophrenia, suicide attempt), cognitive (intelligence) and socioeconomic (educational attainment, income, social deprivation) outcomes.

RESULTS

We found evidence for a contribution of birth weight to ADHD (OR for 1 s.d. unit decrease (~464 g) in birth weight, 1.29; 95% CI 1.03-1.62), PTSD (OR = 1.69; 95% CI 1.06-2.71) and suicide attempt (OR = 1.39; 95% CI 1.05-1.84), as well as for intelligence (β = -0.07; 95% CI -0.13 to -0.02) and socioeconomic outcomes, i.e. educational attainment (β = -0.05; 95% CI -0.09 to -0.01), income (β = -0.08; 95% CI -0.15 to -0.02) and social deprivation (β = 0.08; 95% CI 0.03-0.13). However, no evidence was found for a contribution of birth weight to the other examined mental health outcomes. Results were consistent across a wide range of sensitivity analyses.

CONCLUSIONS

These findings support the hypothesis that birth weight could be an important element on the causal pathway to mental health, cognitive and socioeconomic outcomes.