Effects of neonatal growth on adult blood pressures of borderline hypertensive rats

Can breastfeeding affect the rest of our life?

The breastfeeding period is one of the most important critical windows in our development, since milk, our first food after birth, contains several compounds, such as macronutrients, micronutrients, antibodies, growth factors and hormones that benefit human health. Indeed, nutritional, and environmental alterations during lactation, change the composition of breast milk and induce alterations in the child's development, such as obesity, leading to the metabolic dysfunctions, cardiovascular diseases and neurobehavioral disorders. This review is based on experimental animal models, most of them in rodents, and summarizes the impact of an adequate breast milk supply in view of the developmental origins of health and disease (DOHaD) concept, which has been proposed by researchers in the areas of epidemiology and basic science from around the world. Here, experimental advances in understanding the programming during breastfeeding were compiled with the purpose of generating knowledge about the genesis of chronic noncommunicable diseases and to guide the development of public policies to deal with and prevent the problems arising from this phenomenon. This review article is part of the special issue on "Cross talk between periphery and brain".

Effect of high-fat diet on stress responsiveness in borderline hypertensive rats

Stress in combination with genetic susceptibility is a factor in the development of hypertension. We used borderline hypertensive rats to investigate whether exposure to high-fat and/or junk-food diet at different stages of ontogeny has programing consequences on stress responses. Wistar dams were fed a high- or low-fat diet for 6 weeks prior to mating with spontaneously hypertensive males, and during gestation. At birth, litters were fostered either to a dam in the same or an alternative diet condition as during gestation. After weaning, male offspring were fed either a control-chow diet or an intermittent junk food fatty diet. Between postnatal days 57-61, half of the rats in each dietary group received daily social defeat sessions using a resident-intruder protocol, and the other half were unstressed controls. Blood pressure was measured indirectly both before and after each defeat session. On the final day, rats were killed for physiological measures. Socially defeated rats showed large increases in serum corticosterone concentration and adrenal hypertrophy, indicating the effectiveness of this non-adapting stressor. Serum corticosterone level was also higher in rats fed with the junk-food diet post-weaning compared with those fed with chow only, but there were no significant effects of gestational or lactational dietary history.

Nitric oxide, superoxide and renal blood flow autoregulation in SHR after perinatal L-arginine and antioxidants

AIM

Nitric oxide (NO) and superoxide are considered to be regulatory in renal blood flow (RBF) autoregulation, and hence may contribute to development of hypertension. To extend our previous observations that dynamic NO release is impaired in the spontaneously hypertensive rat (SHR) we investigated, firstly, if superoxide dependency of RBF autoregulation is increased in SHR and, secondly, if the beneficial effect of perinatal supplementation in SHR is partly as a result of early correction of RBF autoregulation. We hypothesized that perinatal supplementation by restoring dynamic NO release and/or decreasing superoxide dependency and would improve life-long blood pressure regulation.

METHODS

Autoregulation was studied using stepwise reductions in renal perfusion pressure in anaesthetized male SHR, SHR perinatally supplemented with arginine and antioxidants (SHRsuppl) and Wistar-Kyoto (WKY), prior to and during i.v. Nomega-nitro-l-arginine (NO synthase inhibitor) or tempol (superoxide dismutase mimetic).

RESULTS

Spontaneously hypertensive rat displayed a wider operating range of RBF autoregulation as compared with WKY (59 +/- 4 vs. 33 +/- 2 mmHg, respectively; P < 0.01). Perinatal supplementation in SHR decreased mean arterial pressure, renal vascular resistance and the operating range of RBF autoregulation (43 +/- 3 mmHg; P < 0.01). In addition autoregulation efficiency decreased. RBF autoregulation characteristics shifted towards those of normotensive WKY. However, dynamic NO release was still impaired and no clear differences in superoxide dependency in RBF autoregulation between groups was observed.

CONCLUSION

Perinatal supplements shifted RBF autoregulation characteristics of SHR towards WKY, although capacity of the SHRsuppl kidney to modulate NO production to shear stress still seems impaired. The less strictly controlled RBF as observed in perinatally supplemented SHR could result in an improved long-term blood pressure control. This might partly underlie the beneficial effects of perinatal supplementation.

Central and peripheral contributions to obesity-associated hypertension: impact of early overnourishment

Obesity induced by a high-fat diet was associated with increased tail-cuff blood pressure in adult rats. The mechanisms underlying obesity-related hypertension are unclear, but increased sympathetic activation most probably plays a role. Neuroendocrine alterations observed in obesity may influence both feeding patterns and blood pressure. Work from our laboratory has shown that chronic overfeeding in rats leads to changes in neuropeptide Y (NPY) and alpha-melanocyte stimulating hormone (alphaMSH) in the hypothalamus. These peptides have central effects on blood pressure, indicating that obesity-related changes in the CNS may impact on cardiovascular function. Population studies suggest that nutrition in early life can influence the subsequent risk of obesity and high blood pressure. To examine the impact of early postnatal overnutrition on blood pressure and adipose-derived mediators, we adjusted rat litters to 3 or 12 pups (overnutrition and control, respectively). Pups raised in small litters were 15% heavier at weaning, and this intervention was associated with a modest elevation of blood pressure and body weight as adults (16 weeks). Animals raised in small litters had increased 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) mRNA in white adipose tissue as adults, which may impact on cardiovascular function. Adjustment of diet after weaning, to 30% fat diet or standard chow, allowed comparison of the impact of different periods of overnourishment. Implementation of a high-fat diet at weaning overcame the effect of litter size on body weight from 10 weeks of age. Blood pressure rose progressively with high-fat feeding and was positively correlated with leptin and body weight. Chronic consumption of a high-fat diet led to marked increases in leptin and insulin and modest increases in blood pressure, and impacts on brain transmitters implicated in the regulation of both appetite and blood pressure. Overnourishment during early postnatal development led to profound changes in body weight at weaning, which tended to abate with maturation. It also led to long-term changes in some adipose-derived mediators, possibly increasing cardiovascular risk.

Early dietary intervention: long-term effects on blood pressure, brain neuropeptide Y, and adiposity markers

Early life nutrition impacts on subsequent risk of obesity and hypertension. Several brain chemicals responsible for both feeding and cardiovascular regulation are altered in obesity. We examined effects of early postnatal overnutrition on blood pressure, brain neuropeptide Y (NPY), and adiposity markers. Rat pup litters were adjusted to either 3 or 12 male animals (overnutrition and control, respectively) on day 1 of life. After weaning, rats were given either a palatable high-fat diet or standard chow. Smaller litter pups were significantly heavier by 17 days of age. By 16 wk, the effect of litter size was masked by that of diet, postweaning. Small and normal litter animals fed a high-fat diet had similar increases in body weight, plasma insulin, leptin, and adiponectin concentrations, leptin mRNA, and fat masses relative to chow-fed animals. An increase in 11beta-hydroxysteroid dehydrogenase-1 mRNA in white adipose tissue, and a decrease in uncoupling protein-1 mRNA in brown adipose tissue in both small litter groups at 16 wk of age, may represent a programming effect of the altered litter size. NPY concentration in the paraventricular nucleus of the hypothalamus was reduced in high fat-fed groups. Blood pressure was significantly elevated at 13 wk in high-fat-fed animals. This study demonstrates that overnourishment during early postnatal development leads to profound changes in body weight at weaning, which tended to abate with maturation. Thus the effects of long-term dietary intervention postweaning can override those of litter size-induced obesity.

Angiotensin II receptor binding in the locus ceruleus of spontaneously hypertensive rats and Wistar-Kyoto rats: a quantitative autoradiographic study with references to hypertension and cardiac/testicular hypertrophy

The locus ceruleus (LC) contains a high density of angiotensin II (AII) receptors. The role of AII receptors at the LC in genetic hypertension and organ function is unclear. Spontaneously hypertensive (SHR) rats and Wistar-Kyoto (WKY) rats were studied, and blood pressure of animals was measured using the tail-cuff method. Animals were decapitated and the heart weight (HW) and testicular weight (TW) of animals measured. AII receptor binding was carried out by incubating the LC tissue sections with 200 pM [(125)I]-AII receptor ligand, and measured using quantitative autoradiography. Results showed that the HW/BW ratio was significantly higher in SHR rats than WKY rats. However, the TW/BW ratio was higher in SHR rats than WKY rats only at two hypertensive stages, whereas AII receptor binding capacity in the LC was also statistically higher in SHR rats than WKY rats. Results indicated that cardiac and testicular hypertrophies were related to higher AII receptor binding in the LC of SHR rats, when compared with WKY rats. Interestingly, the literature shows that there is an LC-testes axis. In conclusion, this study indicated that AII receptors in the LC are associated with genetic hypertension, and testicular weight could be a reasonable index for essential hypertension.

Ontogenetic aspects of hypertension development: analysis in the rat

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4-10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+ and antihypertensive effects of dietary Ca2+ are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+ are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.

Role of angiotensin II in early cardiovascular growth and vascular amplifier development in spontaneously hypertensive rats

OBJECTIVE

To examine the role played by angiotensin II (AII) in the development of prehypertensive vascular hypertrophy in the spontaneously hypertensive rat (SHR) and to determine whether normalization of prehypertensive vascular hypertrophy attenuates the development of hypertension.

DESIGN

Male SHR and Wistar-Kyoto (WKY) rats were treated from age 10 days until age 6 weeks with perindopril, an angiotensin converting enzyme (ACE) inhibitor, or with losartan, a type 1 AII receptor antagonist.

METHODS

At termination of treatment, or 8 weeks after cessation of treatment, vascular growth was assessed by measurement of hindquarter resistance properties and of the medial cross-sectional area of first-order mesenteric arteries. The growth of the heart was assessed by measurement of the left ventricle:body weight ratio.

RESULTS

Perindopril and losartan treatment of SHR and WKY rats led to a heterogeneous response in the vasculature, resulting in a reduction in perfusion pressures at maximum dilatation and constriction in the hindquarter vasculature but no significant change in medial cross-sectional area of small mesenteric arteries. Neither perindopril nor losartan treatment affected the growth of the left ventricle in the SHR. After the cessation of treatment the development of hypertension in the losartan- and perindopril-treated SHR did not differ from that in controls.

CONCLUSION

These results suggest that AII, acting via angiotensin type 1 receptors, plays an important role in determining the early post-natal reactivity of the hindquarter vasculature but not the medial cross-sectional area of the mesenteric vasculature, which implies that different growth regulatory mechanisms are operating in the two vascular beds. The lack of effect in some vascular beds, together with the lack of effect on the heart, may account for the absence of a persistent effect on the blood pressure.

Enduring effects of infant feeding experiences on adult blood pressure

OBJECTIVE

Vulnerability to psychosomatic diseases is influenced by events early in life. The objective of this article is to discuss animal research that demonstrates relationships between feeding experiences and growth in infancy and risk of hypertension in adulthood.

METHOD

Subjects were spontaneously hypertensive rats (SHR) and their normotensive Wistar Kyoto progenitors. Initial experiments involved observations of the behaviors of rat mothers and their infants and follow-up measurements of blood pressures. Further studies focused on measurements of infant blood pressure during feeding, and recent investigations manipulated weight gain and sex hormones early in life.

RESULTS

Infant rats whose mothers were seen nursing more often had increased blood pressure as adults. Each time rat mothers delivered milk to their young, the nursing pups' blood pressures rose dramatically. These feeding-induced increases in blood pressure have been observed in the young of many species including humans. They are mediated by autonomic nervous system activity and are larger in SHR pups. Finally, animals that gain weight rapidly as infants as a consequence of being reared in small litters had higher adult blood pressure; but, this effect is seen only in intact males.

CONCLUSIONS

Adult physiologic traits can be influenced by the joint actions of genetic predisposition and essential psychosocial interactions during early development. Animal models can stimulate new ideas, provide important confirmations and elaborations of hypotheses from human investigations, and afford experimental approaches for identifying mechanisms underlying the transduction of behavioral experience to disease susceptibility.