Endocrine Abstracts

We recently demonstrated that fetal programming changes induced by a maternal low protein diet (MLP) that lead to the development of hypertension in the rat offspring were associated with increased expression of the AT1b angiotensin receptor (AT1b) and reduced methylation of its promoter in the adrenal gland. Previous findings have suggested that overactivity of the maternal pituitary–adrenal axis in pregnancy results in overexposure of the fetus to glucocorticoids which in turn lead to the changes in gene expression and ultimately the long term pathological consequences. We aimed to test whether glucocorticoids are central to the low protein effect by treating rat dams with metyrapone (5 mg/kg) over days 1–14 of pregnancy. In an alternative paradigm, pregnant mothers were exposed to dexamethasone from day 14 of gestation. Offspring of rats subjected to MLP diet had greater systolic blood pressure (P<0.001), whereas animals treated with metyrapone maintained control levels of blood pressure. Adrenals from 1-week-old animals were used to make cDNA and genomic DNA. Real-time PCR analysis demonstrated that AT1b mRNA was significantly greater in MLP offspring, but administration of metyrapone prevented this overexpression. Bisulphite sequencing of genomic DNA prepared from these adrenals revealed that MLP offspring had significantly less promoter methylation compared to controls. Administration of metyrapone in early pregnancy reversed this trend such that methylation levels were indistinguishable from controls. Measured circulating corticosterone levels showed that animals exposed to metyrapone in utero exhibit grossly normal adrenal function postnatally. Administration of dexamethasone during pregnancy resulted in hypertension at four weeks of age, but no difference in adrenal AT1b expression or promoter methylation at one week of age were identified. These findings suggest that maternal adrenal steroids can mediate the AT1b hypomethylation/overexpression phenotype resulting from MLP programming although externally administered glucocorticoid may not have this effect.