No abstract

Abstract-Hypertension is a major risk factor for cardiovascular and cerebrovascular disease. Lifelong environmental factors (eg, salt intake, obesity, alcohol) and genetic factors clearly contribute to the development of hypertension, but it has also been established that stress in utero may program the later development of the disease. This phenomenon, known as fetal programming can be modeled in a range of experimental animal models. In maternal low protein diet rat models of programming, administration of angiotensin converting enzyme inhibitors or angiotensin receptor antagonists in early life can prevent development of hypertension, thus implicating the renin-angiotensin system in this process. Here we show that in this model, expression of the AT 1b angiotensin receptor gene in the adrenal gland is upregulated by the first week of life resulting in increased receptor protein expression consistent with the increased adrenal angiotensin responsiveness observed by others. Furthermore, we show that the proximal promoter of the AT 1b gene in the adrenal is significantly undermethylated, and that in vitro, AT 1b gene expression is highly dependent on promoter methylation. These data suggest a link between fetal insults to epigenetic modification of genes and the resultant alteration of gene expression in adult life leading ultimately to the development of hypertension. It seems highly probable that similar influences may be involved in the development of human hypertension. (Circ Res. 2007;100:520-526.)

1. In the rat, hypertension is induced by fetal exposure to maternal low-protein diets. The effect on blood pressure of undernutrition before conception and during discrete periods in early, mid or late pregnancy was assessed using an 18% casein (control) diet and a 9% casein to apply mild protein restriction. 2. The offspring of rats fed 9% casein developed raised blood pressure by weaning age. Feeding a low-protein diet before conception was not a prerequisite for programming of hypertension. 3. Hypertension was observed in rats exposed to low protein during the following gestational periods: days 0-7, days 8-14 and days 15-22. Blood pressure increases elicited by these discrete periods of undernutrition were lower than those induced by feeding a low-protein diet throughout pregnancy. The effect in early gestation was significant only in male animals. Post-natal growth of male rats exposed to low-protein diets was accelerated, but kidneys were small in relation to body weight. 4. Biochemical indices of glucocorticoid action in liver, hippocampus, hypothalamus and lung were elevated in rats exposed to low-protein diets in utero. The apparent hypersensitivity to glucocorticoids was primarily associated with undernutrition in mid to late gestation. 5. Plasma renin activity was elevated in rats exposed to 9% casein over days 15-55 of gestation. Animals undernourished over days 0-7 and 8-14 produced pups with lower plasma angiotensin II concentrations at weaning. 6. Fetal exposure to maternal low-protein diets for any period in gestation may programme hypertension in the rat. Alterations to renal structure, renal hormone action or the hypothalamic-pituitary-adrenal axis may all play a role in the programming phenomenon, either independently or in concert.