Prenatal programming of rat cortical collecting tubule sodium transport

Prenatal insults have been shown to lead to elevated blood pressure in offspring when they are studied as adults. Prenatal administration of dexamethasone and dietary protein deprivation have demonstrated that there is an increase in transporter abundance for a number of nephron segments but not the subunits of the epithelial sodium channel (ENaC) in the cortical collecting duct. Recent studies have shown that aldosterone is elevated in offspring of protein-deprived mothers when studied as adults, but the physiological importance of the increase in serum aldosterone is unknown. As an indirect measure of ENaC activity, we compared the natriuretic response to benzamil in offspring of mothers who ate a low-protein diet (6%) with those who ate a normal diet (20%) for the last half of pregnancy. The natriuretic response to benzamil was greater in the 6% group (821.1 ± 161.0 μmol/24 h) compared with the 20% group (279.1 ± 137.0 μmol/24 h), consistent with greater ENaC activity in vivo (P < 0.05). In this study, we also directly studied cortical collecting tubule function from adult rats using in vitro microperfusion. There was no difference in basal or vasopressin-stimulated osmotic water permeability. However, while cortical collecting ducts of adult offspring whose mothers ate a 20% protein diet had no sodium transport (-1.9 ± 3.1 pmol·mm(-1)·min(-1)), the offspring of rats that ate a 6% protein diet during the last half of pregnancy had a net sodium flux of 10.7 ± 2.6 pmol·mm(-1)·min(-1) (P = 0.01) in tubules perfused in vitro. Sodium transport was measured using ion-selective electrodes, a novel technique allowing measurement of sodium in nanoliter quantities of fluid. Thus we directly demonstrate that there is prenatal programming of cortical collecting duct sodium transport.     

Postnatal high-fat diet sex-specifically exacerbates prenatal dexamethasone-induced hypertension: Mass spectrometry-based quantitative proteomic approach

Hypertension can originate from pre- and post-natal insults. High-fat (HF) diet and prenatal dexamethasone (DEX) exposure are both involved in hypertension of developmental origins. We examined whether postnatal HF diet sex-specifically increases the vulnerability to prenatal DEX exposure-induced programmed hypertension in adult offspring. Additionally, we sought to identify candidate proteins involved in programmed hypertension through a mass spectrometry-based quantitative proteomic approach. Male and female offspring were studied separately: control, DEX, HF, and DEX + HF (n=8/group). Pregnant Sprague–Dawley rats received dexamethasone (0.1 mg/kg body weight) or vesicle from gestational day 16–22. Offspring received high-fat diet (D12331, Research Diets) or regular diet from weaning to 4 months of age. Rats were sacrificed at 4 months of age. We found that postnatal HF diet increased vulnerability of prenatal DEX-induced hypertension in male but not in female adult offspring. Additionally, HF and DEX elicited renal programming in a sex-specific fashion. In males, DEX + HF increased renal parvalbumin (PVALB) and carbonic anhydrase III (CA III) protein levels. While prenatal DEX down-regulated PVALB and CA III protein abundance in female offspring kidneys. Moreover, DEX + HF increased renal protein level of type 3 sodium hydrogen exchanger (NHE3) in males but not in females. In conclusion, postnatal HF diet and prenatal DEX exposure synergistically induced programmed hypertension in male-only offspring. DEX + HF induced sex-specific alterations of protein profiles in offspring kidneys. By identifying candidate proteins underlying sex-specific mechanisms, our results could lead to novel offspring sex-specific interventions to prevent hypertension induced by antenatal corticosteroids and postnatal HF intake in both sexes.     

Prenatal programming of rat proximal tubule Na+/H+ exchanger by dexamethasone

Prenatal administration of dexamethasone causes hypertension in rats when they are studied as adults. Although an increase in tubular sodium reabsorption has been postulated to be a factor programming hypertension, this has never been directly demonstrated. The purpose of this study was to examine whether prenatal programming by dexamethasone affected postnatal proximal tubular transport. Pregnant Sprague-Dawley rats were injected with intraperitoneal dexamethasone (0.2 mg/kg) daily for 4 days between the 15th and 18th days of gestation. Prenatal dexamethasone resulted in an elevation in systolic blood pressure when the rats were studied at 7-8 wk of age compared with vehicle-treated controls: 131 +/- 3 vs. 115 +/- 3 mmHg (P < 0.001). The rate of proximal convoluted tubule volume absorption, measured using in vitro microperfusion, was 0.61 + 0.07 nl.mm(-1).min(-1) in control rats and 0.93+ 0.07 nl.mm(-1).min(-1) in rats that received prenatal dexamethasone (P < 0.05). Na(+)/H(+) exchanger activity measured in perfused tubules in vitro using the pH-sensitive dye BCECF showed a similar 50% increase in activity in proximal convoluted tubules from rats treated with prenatal dexamethasone. Although there was no change in abundance of NHE3 mRNA, the predominant luminal proximal tubule Na(+)/H(+) exchanger, there was an increase in NHE3 protein abundance on brush-border membrane vesicles in 7- to 8-wk-old rats receiving prenatal dexamethasone. In conclusion, prenatal administration of dexamethasone in rats increases proximal tubule transport when rats are studied at 7-8 wk old, in part by stimulating Na(+)/H(+) exchanger activity. The increase in proximal tubule transport may be a factor mediating the hypertension by prenatal programming with dexamethasone.     

Sex differences in postnatal growth and renal development in offspring of rabbit mothers with chronic secondary hypertension

Previously, we demonstrated that adult blood pressure was increased in offspring of rabbit mothers with chronic secondary renal hypertension. Our study identified sex-specific differences in the programming of hypertension, with female, not male, offspring, having increased blood pressure at 30 wk of age. The aim of this study was to characterize the maternal hypertension during pregnancy to determine potential programming stimuli. Further, we examined the impact of chronic maternal hypertension on offspring birth weight, nephron number, and renal noradrenaline content (as an index of renal innervation density). Three groups of mothers and their offspring were studied: two-kidney, one-wrap (2K-1W, n = 9 mothers) hypertensive, two-kidney, two-wrap (2K-2W, n = 8) hypertensive, and a sham-operated group (n = 9). Mean arterial blood pressure was increased by approximately 20 mmHg throughout pregnancy in both hypertensive groups compared with sham mothers (P(G) < 0.001). Plasma renin activity (PRA; P(G) < 0.05) and aldosterone (P(G) < 0.05) levels were increased during gestation in the 2K-1W, but not the 2K-2W mothers. Birth weight was increased by approximately 20% in offspring of both groups of hypertensive mothers (P(T) < 0.001), though this was associated with a reduction in litter size. Renal noradrenaline content was increased ( approximately 40%, P < 0.05) at 5 wk of age in female 2K-1W offspring compared with sham offspring. Glomerular number was not reduced in female offspring of either group of hypertensive mothers; however, glomerular tuft volume was reduced in female 2K-2W offspring (P < 0.05), indicative of a reduction in glomerular filtration surface area. In conclusion, the two models of renal hypertension produced differential effects on the offspring. The impact of a stimulated maternal renin-angiotensin system in the 2K-1W model of hypertension may influence development of the renal sympathetic nerves and contribute to programming of adult hypertension.     

Prenatal stress programs lipid metabolism enhancing cardiovascular risk in the female F1, F2, and F3 generation in the primate model common marmoset (Callithrix jacchus)

Background Many human diseases are modulated by intrauterine environment, which is called prenatal programming. This study investigated effects of prenatal glucocorticoids on the lipid metabolism of three filial generations of common marmosets. Methods Pregnant primates were treated with dexamethasone during pregnancy. Body weight and blood lipid parameters of adult female offspring (F1: n = 5, F2: n = 6, F3: n = 3) were compared with age‐related female controls (n = 12). Results F1, F2, and F3 offspring showed significantly lower percentage of plasma n3 fatty acids than controls. F2 and F3 presented higher cholesterol levels, with significantly more LDL cholesterol, significantly less HDL triglycerides and an enhanced cholesterol/HDL cholesterol ratio. Body weight was not significantly affected. Conclusions Prenatal dexamethasone led to higher amounts of cardiovascular risk factors and less protective parameters in female F1–F3 offspring. The intergenerational consequences suggest prenatal programming through epigenetic effects.     

Primary hyperaldosteronism suppressed after glucocorticoid administration]

Authors present a case of glucocorticoid suppressible hyperaldosteronism in 18 year old female. Unmeasurable low plasma renin activity and marked increase in aldosterone concentration was established. After administration of dexamethasone, normalization of aldosterone concentration and blood pressure has been observed.     

Role of maternal glucocorticoid inducible kinase SGK1 in fetal programming of blood pressure in response to prenatal diet

Maternal stress and malnutrition modify intrauterine fetal development with impact on postnatal blood pressure, nutrient, water, and electrolyte metabolism. The present study explored the possible involvement of maternal serum- and glucocorticoid-inducible kinase (SGK)-1 in fetal programming of blood pressure. To this end, wild-type (sgk1(+/+)) male mice were mated with SGK1 knockout (sgk1(-/-)) female mice, and sgk1(-/-) males with sgk1(+/+) females, resulting in both cases in heterozygotic (sgk1(-/+)) offspring. Following prenatal protein restriction, the offspring of sgk1(+/+) mothers gained weight significantly slower and had significantly higher blood pressure after birth. Moreover, a sexual dimorphism was apparent in fasting blood glucose and plasma corticosterone concentrations, with higher levels in female offspring. In contrast, prenatal protein restriction of sgk1(-/-) mothers had no significant effect on postnatal weight gain, blood pressure, plasma glucose concentration, or corticosterone levels, irrespective of offspring sex. Plasma aldosterone concentration, urinary flow rates, and urinary excretions of Na(+) and K(+) were not significantly modified by either maternal genotype or nutritional manipulation. In conclusion, maternal signals mediated by SGK1 may play a decisive role in fetal programming of hypertension induced by prenatal protein restriction.     

Direct and dam-mediated effects of prenatal dexamethasone on emotionality, cognition and HPA axis in adult Wistar rats

Prenatal stress can affect foetal neurodevelopment and result in increased risk of depression in adulthood. It promotes increased maternal hypothalamo–pituitary–adrenal gland (HPA) secretion of glucocorticoid (GC), leading to increased foetal and maternal GC receptor activity. Prenatal GC receptor activity is also increased during prenatal treatment with dexamethasone (DEX), which is commonly prescribed as a prophylactic treatment of preterm delivery associated morbid symptoms. Here, we exposed pregnant Wistar rats to 0.1 mg/kg/d DEX during the last week of pregnancy and performed cross-fostering at birth. In the adult offspring we then studied the effects of prenatal DEX exposure per se and the effects of rearing by a dam exposed to prenatal DEX. Offspring were assessed in the following paradigms testing biobehavioural processes that are altered in depression: progressive ratio schedule of reinforcement (anhedonia), Porsolt forced swim test (behavioural despair), US pre-exposure active avoidance (learned helplessness), Morris water maze (spatial memory) and HPA axis activity (altered HPA function). Responsiveness to a physical stressor in terms of HPA activity was increased in male offspring exposed prenatally to DEX. Despite this increased HPA axis reactivity, we observed no alteration of the assessed behaviours in offspring exposed prenatally to DEX. We observed impairment in spatial memory in offspring reared by DEX exposed dams, independently of prenatal treatment. This study does not support the hypothesis that prenatal DEX exposure leads to depression-like symptoms in rats, despite the observed sex-specific programming effect on HPA axis. It does however emphasise the importance of rearing environment on adult cognitive performances.     

Castrated autoimmune glomerulonephritis mouse model shows attenuated glomerular sclerosis with altered parietal epithelial cell phenotype

Sex hormones help in maintaining proper immunity as well as renal homeostasis in mammals, and these multi-functional properties characterize the onset of sex-dependent diseases. To clarify the contribution of sex hormones to autoimmune disease-related renal pathogenesis, BXSB/MpJ-Yaa was investigated as a murine autoimmune glomerulonephritis model. BXSB/MpJ-Yaa and its wild-type, BXSB/MpJ-Yaa⁺ were castrated or sham-operated at three weeks and examined until six months of age. Both castrated strains showed significantly lower serum testosterone levels and body weights than sham-operated mice. Castration did not change the disease phenotypes in BXSB/MpJ-Yaa⁺. At three months, both sham-operated and castrated BXSB/MpJ-Yaa manifested splenomegaly, autoantibody production, and glomerulonephritis, and castrated BXSB/MpJ-Yaa tended to show heavier spleen weights than the sham-operated group. At six months, both the treated BXSB/MpJ-Yaa showed equivalent autoimmune disease conditions; however, castrated mice clearly showed milder glomerular sclerotic lesions than the sham-operated groups. Urinary albumin excretion in castrated BXSB/MpJ-Yaa was significantly milder than in sham-operated mice at four months, but those of both the treated BXSB/MpJ-Yaa were comparable at six months. The examined renal histopathological indices in parietal epithelial cells were remarkably altered by castration. Briefly, castration decreased the height of parietal epithelial cells and total parietal epithelial cell number in BXSB/MpJ-Yaa at six months. For immunostaining, parietal epithelial cells facing the injured glomeruli of BXSB/MpJ-Yaa expressed CD44, an activated parietal epithelial cell marker, and CD44-positive parietal epithelial cells showed nuclear localization of the androgen receptor and proliferation marker Ki67. CD44- or Ki67-positive parietal epithelial cells were significantly fewer in castrated group than in sham-operated BXSB/MpJ-Yaa at six months. Further, quantitative indices for CD44-positive parietal epithelial cell number and frequency in renal corpuscles positively correlated with glomerular sclerotic severity in BXSB/MpJ-Yaa. In conclusion, androgen seemed to have an effect on both systemic immunity and renal morpho-function; however, the effect on the latter could be more clearly observed in BXSB/MpJ-Yaa, as parietal epithelial cell activation resulted in glomerular sclerosis.     

Maternal high-sodium intake alters the responsiveness of the renin-angiotensin system in adult offspring

AimsThe goal of the current study was to evaluate the impact of maternal sodium intake during gestation on the systemic and renal renin–angiotensin–aldosterone-system (RAAS) of the adult offspring.Main methodsFemale Wistar rats were fed high- (HSD-8.0% NaCl) or normal-sodium diets (NSD-1.3% NaCl) from 8 weeks of age until the delivery of their first litter. After birth, the offspring received NSD. Tail-cuff blood pressure (TcBP) was measured in the offspring between 6 and 12 weeks of age. At 12 weeks of age, the offspring were subjected to either one week of HSD or low sodium diet (LSD-0.16% NaCl) feeding to evaluate RAAS responsiveness or to acute saline overload to examine sodium excretory function. Plasma (PRA) and renal renin content (RRC), serum aldosterone (ALDO) levels, and renal cortical and medullary renin mRNA expression levels were evaluated at the end of the study.Key findingsTcBP was higher among dams fed HSD, but no TcBP differences were observed among the offspring. Male offspring, however, exhibited increased TcBP after one week of HSD feeding, and this effect was independent of maternal diet. Increased RAAS responsiveness to the HSD and LSD was also observed in male offspring. The baseline levels of PRA, ALDO, and cortical and medullary renin gene expression were lower but the RRC levels were higher among HSD-fed male offspring (HSDoff). Conversely, female HSDoff showed reduced sodium excretion 4 h after saline overload compared with female NSDoff.SignificanceHigh maternal sodium intake is associated with gender-specific changes in RAAS responsiveness among adult offspring.     

Prenatal Exposure to Dexamethasone in the Mouse Alters Cardiac Growth Patterns and Increases Pulse Pressure in Aged Male Offspring

Exposure to synthetic glucocorticoids during development can result in later cardiovascular and renal disease in sheep and rats. Although prenatal glucocorticoid exposure is associated with impaired renal development, less is known about effects on the developing heart. This study aimed to examine the effects of a short-term exposure to dexamethasone (60 hours from embryonic day 12.5) on the developing mouse heart, and cardiovascular function in adult male offspring. Dexamethasone (DEX) exposed fetuses were growth restricted compared to saline treated controls (SAL) at E14.5, but there was no difference between groups at E17.5. Heart weights of the DEX fetuses also tended to be smaller at E14.5, but not different at E17.5. Cardiac AT_1aR, Bax, and IGF-1 mRNA expression was significantly increased by DEX compared to SAL at E17.5. In 12-month-old offspring DEX exposure caused an increase in basal blood pressure of ∼3 mmHg. In addition, DEX exposed mice had a widened pulse pressure compared to SAL. DEX exposed males at 12 months had an approximate 25% reduction in nephron number compared to SAL, but no difference in cardiomyocyte number. Exposure to DEX in utero appears to adversely impact on nephrogenesis and heart growth but is not associated with a cardiomyocyte deficit in male mice in adulthood, possibly due to compensatory growth of the myocardium following the initial insult. However, the widened pulse pressure may be indicative of altered vascular compliance.     

Fetal renal and blood pressure responses to steroid infusion after early prenatal treatment with dexamethasone

Maternal infusion of dexamethasone for 48 h early in gestation results in upregulation of mRNA for mineralocorticoid and glucocorticoid (MR and GR) receptors and angiotensin II receptors in ovine fetal kidneys late in gestation. This study sought to determine whether dexamethasone exposure results in changes in renal function and blood pressure responsiveness to infused cortisol or aldosterone in the late-gestation fetus. Merino ewes carrying single fetuses were infused with isotonic saline (Sal; n = 9) or dexamethasone (Dex, 0.48 mg/h; n = 10) for 48 h between days 26 and 28 of gestation (term = 150 days). At 115-122 days, renal function and blood pressure were measured in fetuses during a 4-h infusion of saline, cortisol (100 microg/h), or aldosterone (5 microg/h). Infusions were given in random order at least 2 days apart. Basal blood pressure and renal function were similar in Sal and Dex groups and did not change over the course of saline infusion. Cortisol infusion caused similar increases in blood pressure, urine flow, and glomerular filtration rate (GFR) in the groups. Aldosterone infusion caused a significantly different GFR response between the groups [P(treatment x time) < 0.05], but increase in K excretion and decrease in Na-to-K ratio were similar in the groups. The similar results obtained with cortisol and aldosterone infusion suggest no increased renal functional maturity to those hormones after early prenatal dexamethasone exposure. This suggests that changes in mRNA for MR and GR in kidneys of dexamethasone-exposed fetuses do not result in functional differences and highlights the renin-angiotensin system, as reported previously, as more important in this model.     

Hormonal and renal responses to converting enzyme inhibition during maximal exercise

The role of angiotensin II in the hormonal and renal responses to maximal exercise was investigated by using the angiotensin-converting enzyme inhibitor captopril. Nine male subjects performed a standardized maximal treadmill test with and without acute captopril treatment (25 mg orally). At rest, captopril elevated plasma renin activity and lowered aldosterone levels. With maximal exercise, captopril treatment reduced the increase in mean arterial blood pressure by 8 mmHg and the increase in plasma renin activity by 3.0 ng ANG I.ml-1.h-1. The responses of adrenocorticotropin (ACTH), cortisol, and vasopressin to maximal exercise were not altered by captopril treatment. Although aldosterone levels were reduced at rest with captopril, during maximal exercise no difference was noted between treatments. Captopril treatment had no effects on the renal handling of salts or water during exercise. In conclusion, angiotensin II plays a role in the increase in mean blood pressure during maximal exercise in normal subjects but has no effect on the exercise responses of ACTH, vasopressin, and aldosterone or on the renal handling of salts and water.     

Maternal glucocorticoids and prenatal programming of hypertension

Maternal glucocorticoids have been postulated to play an important role in prenatal programming for adult hypertension in the offspring. However, we have shown previously that offspring hypertension caused by maternal dexamethasone subcutaneous administration at 100 microg x kg(-1) x day(-1) can be accounted for by the corresponding reduction in food intake that these mothers experience. The present studies were designed to determine whether there is a lower dose of dexamethasone that does not reduce maternal food intake yet still causes hypertension in the adult offspring. Pregnant rats were treated with subcutaneous dexamethasone at 50 (D50) or 25 (D25) microg x kg(-1) x day(-1) on days 15-20 of pregnancy. An additional group was untreated or received vehicle injections (control). D25 and D50 dams reduced their food intake by 17% during and after treatment and gained 31% less weight than control over the course of gestation. In adulthood ( approximately 21 wk), chronically instrumented male offspring of D50 and D25 had normal blood pressures (D50: 131 +/- 2 mmHg and D25: 127 +/- 3 mmHg vs. 127 +/- 2 mmHg in control). Qualitatively similar results were found in female offspring. Thus neither dexamethasone per se at these doses nor the accompanying modest reductions in maternal food intake and weight gain have blood pressure programming effects. As far as has been tested, there does not appear to be a dose of dexamethasone that, given over this time period in the rat, programs offspring hypertension without reducing maternal food intake and weight gain. These data do not support the hypothesis that maternal glucocorticoids program offspring hypertension directly.     

Focus: The Science of Stress: The Impact of Maternal Antioxidants on Prenatal Stress Effects on Offspring Neurobiology and Behavior

Prenatal stress is a neuropsychiatric risk factor, and effects may be mediated by prenatal oxidative stress. Cell types in the brain sensitive to oxidative stress—cortical microglia and cortical and hippocampal interneurons—may be altered by oxidative stress generated during prenatal stress and may be neurobiological substrates for altered behavior. Our objective was to determine the critical nature of oxidative stress in prenatal stress effects by manipulating prenatal antioxidants. CD1 mouse dams underwent restraint embryonic day 12 to 18 three times daily or no stress and received intraperitoneal injections before each stress period of vehicle, N-acetylcysteine (200 mg/kg daily), or astaxanthin (30 mg/kg before first daily stress, 10 mg/kg before second/third stresses). Adult male and female offspring behavior, microglia, and interneurons were assessed. Results supported the hypothesis that prenatal stress-induced oxidative stress affects microglia; microglia ramification increased after prenatal stress, and both antioxidants prevented these effects. In addition, N-acetylcysteine or astaxanthin was effective in preventing distinct male and female interneuron changes; decreased female medial frontal cortical parvalbumin interneurons was prevented by either antioxidant; increased male medial frontal cortical parvalbumin interneurons was prevented by N-acetylcysteine and decreased male hippocampal GAD67GFP+ cells prevented by astaxanthin. Prenatal stress-induced increased anxiety-like behavior and decreased sociability were not prevented by prenatal antioxidants. Sensorimotor gating deficits in males was partially prevented by prenatal astaxanthin. This study demonstrates the importance of oxidative stress for persistent impacts on offspring cortical microglia and interneurons, but did not link these changes with anxiety-like, social, and sensorimotor gating behaviors.     

Prenatal high-salt diet in the Sprague-Dawley rat programs blood pressure and heart rate hyperresponsiveness to stress in adult female offspring

Several animal models have been developed to study fetal programming of hypertension. One model involves feeding high-salt (HS) diet to rats before and during pregnancy, during lactation, and after weaning for 10 days. In the present investigation, we limited HS diet to the prenatal period in an attempt to find a narrower critical window for fetal programming. The HS diet did not result in low-birth weight offspring. In the adult offspring, radiotelemetry was used to assess blood pressure and heart rate in the conscious unstressed state. As adults, the HS offspring were not hypertensive compared with normal-salt (NS) control animals. However, the pressor and tachycardic responses to 1-h of restraint were significantly enhanced in HS female offspring, and recovery after restraint was delayed. This was accompanied by an increase in relative expression of corticotropin-releasing hormone (CRH) mRNA in the paraventricular nucleus of the hypothalamus during basal and stressed conditions. There was no augmented stress response or relative increase in CRH mRNA in adult HS male offspring. When challenged with 1 wk of 8% NaCl diet as adults, neither HS male nor female offspring exhibited salt sensitivity compared with NS groups. These data show that a high-salt diet limited to the prenatal period is not sufficient to program hypertension in adult offspring. However, this narrower critical period is sufficient to imprint a lasting hyperresponsiveness to stress, at least in adult female offspring. These data indicate that excessive maternal salt intake during pregnancy can adversely affect the cardiovascular health of adult offspring.     

Regulation of epithelial Na+ channels by adrenal steroids: mineralocorticoid and glucocorticoid effects

Epithelial Na+ channels (ENaC) can be regulated by both mineralocorticoid and glucocorticoid hormones. In the mammalian kidney, effects of mineralocorticoids have been extensively studied, but those of glucocorticoids are complicated by metabolism of the hormones and cross-occupancy of mineralocorticoid receptors. Here, we report effects of dexamethasone, a synthetic glucocorticoid, on ENaC in the rat kidney. Infusion of dexamethasone (24 μg/day) for 1 wk increased the abundance of αENaC 2.26 ± 0.04-fold. This was not accompanied by an induction of Na+ currents (I(Na)) measured in isolated split-open collecting ducts. In addition, hormone treatment did not increase the abundance of the cleaved forms of either αENaC or γENaC or the expression of βENaC or γENaC protein at the cell surface. The absence of hypokalemia also indicated the lack of ENaC activation in vivo. Dexamethasone increased the abundance of the Na+ transporters Na+/H+ exchanger 3 (NHE3; 1.36 ± 0.07-fold), Na(+)-K(+)-2Cl(-) cotransporter 2 (NKCC2; 1.49 ± 0.07-fold), and Na-Cl cotransporter (NCC; 1.72 ± 0.08-fold). Surface expression of NHE3 and NCC also increased with dexamethasone treatment. To examine whether glucocorticoids could either augment or inhibit the effects of mineralocorticoids, we infused dexamethasone (60 μg/day) together with aldosterone (12 μg/day). Dexamethasone further increased the abundance of αENaC in the presence of aldosterone, suggesting independent effects of the two hormones on this subunit. However, I(Na) was similar in animals treated with dexamethasone+aldosterone and with aldosterone alone. We conclude that dexamethasone can occupy glucocorticoid receptors in cortical collecting duct and induce the synthesis of αENaC. However, this induction is not sufficient to produce an increase in functional Na+ channels in the apical membrane, implying that the abundance of αENaC is not rate limiting for channel formation in the kidney.     

Prenatal programming of adult blood pressure: role of maternal corticosteroids

Both maternal glucocorticoid administration and maternal dietary protein or food restriction in pregnancy cause fewer nephrons and hypertension in the adult offspring. The purpose of these studies was to determine the extent to which nutritional factors contribute to programming of offspring hypertension by maternal glucocorticoids. Pregnant rats were treated with dexamethasone (100 microg x kg(-1) x d(-1) sc) on days 1-10 (ED) or days 15-20 (LD) of pregnancy. Additional groups of pregnant animals were pair fed to the early (EDPF) and late (LDPF) dexamethasone-treated groups, and another group was untreated or given vehicle (C). The dams treated with dexamethasone reduced their food intake and lost or failed to gain a normal amount of weight during treatment; body weights of ED dams caught up to normal after the treatment period, whereas those of LD dams did not. In adulthood ( approximately 21 wks), chronically instrumented male offspring of ED had normal blood pressures (125 +/- 2 mmHg vs. 126 +/- 1 mmHg in C), whereas LD offspring were hypertensive (136 +/- 3 mmHg). However, LDPF offspring were equally hypertensive (134 +/- 2 mmHg). Glomerular filtration rates normalized to body weight were not significantly different among groups. Qualitatively similar results were found in female offspring. Thus the long-term effects of maternal glucocorticoid administration at this dose on offspring's blood pressure may, in large part, be accounted for by the reduction in maternal food intake. These data suggest that maternal glucocorticoids and maternal food or protein restriction may, at least in part, share a common mechanism in programming offspring for hypertension. The window of sensitivity of future offspring blood pressure to either maternal insult coincides with nephrogenesis in the rat, suggesting that impaired renal development could play an important role in this programming.     

Effects of K+-deficient diets with and without NaCl supplementation on Na+, K+, and H2O transporters' abundance along the nephron

Dietary potassium (K(+)) restriction and hypokalemia have been reported to change the abundance of most renal Na(+) and K(+) transporters and aquaporin-2 isoform, but results have not been consistent. The aim of this study was to reexamine Na(+), K(+) and H(2)O transporters' pool size regulation in response to removing K(+) from a diet containing 0.74% NaCl, as well as from a diet containing 2% NaCl (as found in American diets) to blunt reducing total diet electrolytes. Sprague-Dawley rats (n = 5-6) were fed for 6 days with one of these diets: 2% KCl, 0.74% NaCl (2K1Na, control chow) compared with 0.03% KCl, 0.74% NaCl (0K1Na); or 2% KCl, 2%NaCl (2K2Na) compared with 0.03% KCl, 2% NaCl (0K2Na, Na(+) replete). In both 0K1Na and 0K2Na there were significant decreases in: 1) plasma [K(+)] (<2.5 mM); 2) urinary K(+) excretion (<5% of control); 3) urine osmolality and plasma [aldosterone], as well as 4) an increase in urine volume and medullary hypertrophy. The 0K2Na group had the lowest [aldosterone] (172.0 ± 17.4 pg/ml) and lower blood pressure (93.2 ± 4.9 vs. 112.0 ± 3.1 mmHg in 2K2Na). Transporter pool size regulation was determined by quantitative immunoblotting of renal cortex and medulla homogenates. The only differences measured in both 0K1Na and 0K2Na groups were a 20-30% decrease in cortical β-ENaC, 30-40% increases in kidney-specific Ste20/SPS1-related proline/alanine-rich kinase, and a 40% increase in medullary sodium pump abundance. The following proteins were not significantly changed in both the 0 K groups: Na(+)/H(+) exchanger isoform 3; Na(+)-K(+)-Cl(-) cotransporter; Na(+)-Cl(-) cotransporter, oxidative stress response kinase-1; renal outer medullary K(+) channel; autosomal recessive hypercholesterolemia; c-Src, aquaporin 2 isoform; or renin. Thus, despite profound hypokalemia and renal K(+) conservation, we did not confirm many of the changes that were previously reported. We predict that changes in transporter distribution and activity are likely more important for conserving K(+) than changes in total abundance.     

Altered health outcomes in adult offspring of Sprague Dawley and Wistar rats undernourished during early or late pregnancy

BACKGROUND: Birth weight in humans has been inversely associated with adult disease risk. Results of animal studies have varied depending on species, strain, and treatment. METHODS: We compared birth weight and adult health in offspring following 50% maternal undernutrition on gestation days (GD) 1–15 (UN1–15) or GD 10–21 (UN10–21) in Sprague Dawley and Wistar rats. Offspring from food‐deprived dams were weighed and cross‐fostered to control dams. Litters were weighed during lactation and initiating at weaning males were fed either control or a high‐fat diet. Young and mature adult offspring were evaluated for obesity, blood pressure (BP), insulin response to oral glucose, and serum lipids. Nephron endowment, renal glucocorticoid receptor, and renin–aldosterone–angiotensin system components were measured. RESULTS: The UN10–21 groups had birth weights lower than controls and transient catch up growth by weaning. Neither strain demonstrated obesity or dyslipidemia following prenatal undernutrition, but long‐term body weight deficits occurred in the UN groups of both strains. High‐fat diet fed offspring gained more weight than control offspring without an effect of prenatal nutrition. Sprague Dawley were slightly more susceptible than Wistar rats to altered insulin response and increased BP following gestational undernutrition. Nephron endowment in Sprague Dawley but not Wistar offspring was lower in the UN10–21 groups. Glucocorticoid and renin–aldosterone–angiotensin system pathways were not altered. CONCLUSIONS: The most consistent effect of maternal undernutrition was elevated BP in offspring. Long‐term health effects occurred with undernutrition during either window, but the UN10–21 period resulted in lower birth weight and more severe adult health effects. Birth Defects Res (Part B) 89:396–407, 2010. © 2010 Wiley‐Liss, Inc.