Effects of maternal dexamethasone treatment on pancreatic β cell function in the pregnant mare and post natal foal

Identification and validation of reference genes for RT-qPCR analysis in fetal rat pancreas

The choice of reference gene is crucial for quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR) assay. To screen and determine the suitable reference genes in fetal rat pancreas, we selected eight candidate reference genes (Gapdh, Actb, Rn18 s, B2m, Rpl13a, Tbp, Ywhaz and Ubc), and evaluated the constancy of gene expression from fetal rat pancreases in non-pathological situation and prenatal dexamethasone exposure (PDE) model, using four algorithms: GeNorm, NormFinder, Bestkeeper and Comparative ΔCt method. In addition, the alteration of mRNA levels of pancreatic insulin was compared between control and PDE groups to validate the reliability of selected reference genes for data normalization of RT-qPCR. The comprehensive ranking of reference genes under physiological condition was as follow: Gapdh > Actb > Ywhaz > Ubc > Rn18s > Rpl13a > B2m > Tbp (female); Actb > Ywhaz > Gapdh > Ubc > B2m > Rpl13a > Rn18 s | Tbp (male). The top ranking reference genes were also stably expressed in PDE fetal pancreas. The best reference gene combinations are: Ywhaz+Actb for female and Ywhaz+Gapdh for male fetal rat pancreas, respectively. Compared with low ranking or single reference gene, the change trend of insulin mRNA normalized by the best reference gene combination between control and PDE groups was more significant and consistent with that of serum insulin level. In conclusion, our results provided the optimal combination of stable reference genes for RT-qPCR assay in pancreatic developmental toxicity study.

Neonatal glucocorticoid overexposure alters cardiovascular function in young adult horses in a sex-linked manner

Prenatal glucocorticoid overexposure has been shown to programme adult cardiovascular function in a range of species, but much less is known about the long-term effects of neonatal glucocorticoid overexposure. In horses, prenatal maturation of the hypothalamus-pituitary-adrenal axis and the normal prepartum surge in fetal cortisol occur late in gestation compared to other precocious species. Cortisol levels continue to rise in the hours after birth of full-term foals and increase further in the subsequent days in premature, dysmature and maladapted foals. Thus, this study examined the adult cardiovascular consequences of neonatal cortisol overexposure induced by adrenocorticotropic hormone administration to full-term male and female pony foals. After catheterisation at 2-3 years of age, basal arterial blood pressures (BP) and heart rate were measured together with the responses to phenylephrine (PE) and sodium nitroprusside (SNP). These data were used to assess cardiac baroreflex sensitivity. Neonatal cortisol overexposure reduced both the pressor and bradycardic responses to PE in the young adult males, but not females. It also enhanced the initial hypotensive response to SNP, slowed recovery of BP after infusion and reduced the gain of the cardiac baroreflex in the females, but not males. Basal diastolic pressure and cardiac baroreflex sensitivity also differed with sex, irrespective of neonatal treatment. The results show that there is a window of susceptibility for glucocorticoid programming during the immediate neonatal period that alters cardiovascular function in young adult horses in a sex-linked manner.

Physiological development of the equine fetus during late gestation

In many species, the pattern of growth and physiological development in utero has an important role in determining not only neonatal viability but also adult phenotype and disease susceptibility. Changes in fetal development induced by a range of environmental factors including maternal nutrition, disease, placental insufficiency and social stresses have all been shown to induce adult cardiovascular and metabolic dysfunction that often lead to ill health in later life. Compared to other precocious animals, much less is known about the physiological development of the fetal horse or the longer-term impacts on its phenotype of altered development in early life because of its inaccessibility in utero, large size and long lifespan. This review summaries the available data on the normal metabolic, cardiovascular and endocrine development of the fetal horse during the second half of gestation. It also examines the responsiveness of these physiological systems to stresses such as hypoglycaemia and hypotension during late gestation. Particular emphasis is placed on the role of the equine placenta and fetal endocrine glands in mediating the changes in fetal development seen towards term and in response to nutritional and other environmental cues. The final part of the review presents the evidence that the early life environment of the horse can alter its subsequent metabolic, cardiovascular and endocrine phenotype as well as its postnatal growth and bone development. It also highlights the immediate neonatal environment as a key window of susceptibility for programming of equine phenotype. Although further studies are needed to identify the cellular and molecular mechanisms involved, developmental programming of physiological phenotype is likely to have important implications for the health and potential athletic performance of horses, particularly if born with abnormal bodyweight, premature or dysmature characteristics or produced by assisted reproductive technologies, indicative of an altered early life environment.

Impact of prematurity for pancreatic islet and beta-cell development

As increasing numbers of babies born preterm survive into adulthood, it is becoming clear that, in addition to the well-described risks of neurodevelopmental sequelae, there also are increased risks for non-communicable diseases, including diabetes. Epidemiological studies indicate that risks are increased even for birth at late preterm and early term gestations and for both type 1 and type 2 diabetes. Thus, factors related to preterm birth likely affect development of the fetal and neonatal beta-cell in addition to effects on peripheral insulin sensitivity. These factors could operate prior to preterm birth and be related to the underlying cause of preterm birth, to the event of being born preterm itself, to the postnatal care of the preterm neonate or to a combination of these exposures. Experimental evidence indicates that factors may be operating during all these critical periods to contribute to altered development of beta-cell mass in those born preterm. Greater understanding of how these factors impact upon development of the pancreas may lead to interventions or management approaches that mitigate the increased risk of later diabetes.

Impact of equine assisted reproductive technologies (standard embryo transfer or intracytoplasmic sperm injection (ICSI) with in vitro culture and embryo transfer) on placenta and foal morphometry and placental gene expression

Assisted reproductive technologies (ARTs) such as intracytoplasmic sperm injection (ICSI), in vitro embryo culture and embryo transfer (ET) may be associated with alterations in fetal and placental development. In horses, ET has been used for decades. More recently, in vitro embryo production by ICSI and in vitro culture, followed by embryo transfer (ICSI-C) has become an accepted method for clinical foal production. However, no information is available on the effects of ICSI-C or even of standard ET itself on placental and neonatal parameters in horses. We therefore evaluated placental and neonatal morphology and placental gene expression in reining- and cutting-type American Quarter Horse foals produced using different technologies. Thirty foals and placentas (naturally conceived (NC), ET and ICSI-C; 10 in each group) were examined morphometrically. The only parameter that differed significantly between groups was the length of the foal upper hindlimb, which was longer in ET and ICSI-C than in NC foals. Evaluation of placental mRNA expression for 17 genes related to growth and vascularisation showed no difference in gene expression between groups. These data indicate that within this population, use of ARTs was not associated with meaningful changes in foal or placental morphometry or in expression of the placental genes evaluated.

Prenatal corticosterone exposure programs sex-specific adrenal adaptations in mouse offspring

Maternal stress can impair foetal development and program sex-specific disease outcomes in offspring through the actions of maternally produced glucocorticoids, predominantly corticosterone (Cort) in rodents. We have demonstrated in mice that male but not female offspring prenatally exposed to Cort (33 µg/kg/h for 60 h beginning at E12.5) develop cardiovascular/renal dysfunction at 12 months. At 6 months of age, renal function was normal but male offspring had increased plasma aldosterone concentrations, suggesting that altered adrenal function may precede disease. This study investigated the long-term impact of prenatal exposure to Cort on adrenal growth, morphology and steroidogenic capacity as well as plasma Cort concentrations in offspring at postnatal day 30 (PN30), 6 months and 12 months of age. Prenatal Cort exposure decreased adrenal volume, particularly of the zona fasciculata, in male offspring at PN30 but increased both relative and absolute adrenal weight at 6 months of age. By 12 months of age, male Cort-exposed offspring had reduced absolute adrenal weight in association with increased adrenal plaque deposition (lipogenic pigmentation). Plasma Cort concentrations were elevated in male 6-month offspring but not at other ages. mRNA expression of Mc2r (ACTH receptor) was increased in males at PN30, and Cyp11a1 expression was decreased at 6 and 12 months of age. There were no changes in the adrenals of female Cort-exposed offspring. This study demonstrates that prenatal Cort exposure induces offspring adrenal gland dysfunction in an age- and sex-specific manner, which may contribute to long-term programmed disease in male offspring after maternal stress.