Programming of hypertonicity in neonatal lambs: resetting of the threshold for vasopressin secretion

In Utero Development of Fetal Thirst and Appetite: Potential for Programming

Thirst and appetite-mediated ingestive behavior develop and are likely programmed in utero, thus preparing for newborn and adult ingestive behavior. Fetal swallowing activity is markedly different from that of the adult, as spontaneous fetal swallowing occurs at a markedly (six-fold) higher rate compared with spontaneous adult drinking activity. This high rate of fetal swallowing is critical for the regulation of amniotic fluid volume and the development of the fetal gastrointestinal tract. Disordered fetal swallowing has been associated with both a decrease (oligohydramnios) and increase (polyhydramnios) in amniotic fluid volume. Both conditions are associated with a significant increase in perinatal morbidity and mortality, and limited treatment modalities are currently available. The mechanisms underlying the high rate of human fetal swallowing are regulated, in part, by tonic activity of central angiotensin II, glutamate N-methyl-D-aspartate receptors, and neuronal nitric oxide synthase. Fetal hypertonicity-mediated dipsogenesis is likely programmed in utero, as offspring of water-restricted ewes demonstrate a programmed syndrome of plasma hypertonicity, with significant hematologic and cardiovascular alterations. Similar to dipsogenic mechanisms, peripheral and central fetal orexic mechanisms also develop in utero, as demonstrated by increased fetal swallowing after both oral sucrose infusion and central injection of neuropeptide Y. The role of leptin in regulating fetal ingestive behavior is interesting because, contrary to actions in adults, leptin does not suppress fetal ingestive behavior. Teleologically, this may be of value during the newborn period, as unopposed appetite stimulatory mechanisms may facilitate rapid fetal and newborn weight gain. An adverse intrauterine environment, with altered fetal orexic factors during the critical developmental period of fetal life, may alter the normal setpoints of appetitive behavior and potentially lead to programming of adulthood hyperphagia and obesity. Further research is needed to delineate the mechanistic relationship between the intrauterine environment and the development of the setpoints of adult appetite and thirst.

In Utero Origins of Hypertension: Mechanisms and Targets for Therapy

The developmental origins of health and disease theory is based on evidence that a suboptimal environment during fetal and neonatal development can significantly impact the evolution of adult-onset disease. Abundant evidence exists that a compromised prenatal (and early postnatal) environment leads to an increased risk of hypertension later in life. Hypertension is a silent, chronic, and progressive disease defined by elevated blood pressure (>140/90 mmHg) and is strongly correlated with cardiovascular morbidity/mortality. The pathophysiological mechanisms, however, are complex and poorly understood, and hypertension continues to be one of the most resilient health problems in modern society. Research into the programming of hypertension has proposed pharmacological treatment strategies to reverse and/or prevent disease. In addition, modifications to the lifestyle of pregnant women might impart far-reaching benefits to the health of their children. As more information is discovered, more successful management of hypertension can be expected to follow; however, while pregnancy complications such as fetal growth restriction, preeclampsia, preterm birth, etc., continue to occur, their offspring will be at increased risk for hypertension. This article reviews the current knowledge surrounding the developmental origins of hypertension, with a focus on mechanistic pathways and targets for therapeutic and pharmacologic interventions.

Early free access to hypertonic NaCl solution induces a long-term effect on drinking, brain cell activity and gene expression of adult rat offspring

Exposure to an altered osmotic environment during a pre/postnatal period can differentially program the fluid intake and excretion pattern profile in a way that persists until adulthood. However, knowledge about the programming effects on the underlying brain neurochemical circuits of thirst and hydroelectrolyte balance, and its relation with behavioral outputs, is limited. We evaluated whether early voluntary intake of hypertonic NaCl solution may program adult offspring fluid balance, plasma vasopressin, neural activity, and brain vasopressin and angiotensinergic receptor type 1a (AT1a)-receptor gene expression. The manipulation (M) period covered dams from 1 week before conception until offspring turned 1-month-old. The experimental groups were (i) Free access to hypertonic NaCl solution (0.45 M NaCl), food (0.18% NaCl) and water [M-Na]; and (ii) Free access to food and water only [M-Ctrol]. Male offspring (2-month-old) were subjected to iv infusion (0.15 ml/min) of hypertonic (1.5M NaCl), isotonic (0.15M NaCl) or sham infusion during 20 min. Cumulative water intake (140 min) and drinking latency to the first lick were recorded from the start of the infusion. Our results indicate that, after systemic sodium overload, the M-Na group had increased water intake, and diminished neuronal activity (Fos-immunoreactivity) in the subfornical organ (SFO) and nucleus of the solitary tract. They also showed reduced relative vasopressin (AVP)-mRNA and AT1a-mRNA expression at the supraoptic nucleus and SFO, respectively. The data indicate that the availability of a rich source of sodium during the pre/postnatal period induces a long-term effect on drinking, neural activity, and brain gene expression implicated in the control of hydroelectrolyte balance.

Offspring born to ewes fed high salt during pregnancy have altered responses to oral salt loads

Prenatal growth is sensitive to the direct and indirect effects of maternal dietary intake; manipulation can lead to behavioural and physiological changes of the offspring later in life. Here, we report on three aspects of how a high-salt diet during pregnancy (conception to parturition) may affect the offspring's response to high oral salt loads: (i) dietary preferences for salt; (ii) response to salt and water balance and aldosterone and arginine vasopressin (AVP) concentrations after an oral salt challenge; (iii) concentrations of insulin and leptin after an oral salt challenge. We used two groups of lambs born to ewes fed either a high-salt (13% NaCl) diet during pregnancy (S lambs; n = 12) or control animals born to ewes fed a conventional (0.5% NaCl) diet during pregnancy (C lambs; n = 12). Lambs were subjected to short- (5 min) and long-term (24 h) preference tests for a high-salt (13% NaCl) or control diet, and the response to an oral challenge with either water or 25% NaCl solution were also carried out. Weaned lambs born to ewes fed high salt during pregnancy did not differ in their preference for dietary salt, but they did differ in their physiological responses to an oral salt challenge. Results indicate that these differences reflect an alteration in the regulation of water and salt balance as the metabolic hormones, insulin and leptin, were not affected. During the first 2 h after a single salt dose, S lambs had a 25% lower water intake compared to the C lambs. S lambs had, on average, a 13% lower AVP concentration than the C lambs (P = 0.014). The plasma concentration of aldosterone was higher in the S lambs than in the C lambs (P = 0.013). Results suggest that lambs born to ewes that ingest high amounts of salt during pregnancy are programmed to have an altered thirst threshold, and blunted response in aldosterone to oral salt loads.

Feeding pregnant ewes a high-salt diet or saltbush suppresses their offspring's postnatal renin activity

If ewes consumed a high-salt diet or saltbush during the last 3 months of pregnancy and for 3 weeks after birth, we expected the renin activity of their lamb to be suppressed at birth and at 3 weeks of age. We also expected an increase in the concentration of cations other than sodium in the ewe's milk and an increase in the plasma Na concentration of the lamb at birth. To test these hypotheses, Merino ewes were fed a high-salt diet (14% NaCl) in an animal house and compared to control ewes eating a control diet (2% NaCl). In addition, we compared ewes grazing saltbush (about 13% salt in diet) to ewes grazing pasture from day 60 of pregnancy to 3 weeks after birth. Lambs born to ewes consuming saltbush had 85% lower (P < 0.001) renin activity than offspring from ewes consuming pasture at 3 weeks of age. Similarly, lambs born to ewes consuming a high-salt diet had 20% lower renin activity at birth and 3 weeks (P = 0.07). Feeding ewes a high-salt diet or saltbush altered the mineral composition of the milk; the largest change was a 10% increase in K levels (P 0.05). Consuming a high-salt diet or saltbush lowered the plasma Na of ewes at 130 days of gestation (by 3-5 mmol/l; P < 0.001), but only lambs from ewes fed the high-salt diet had a lower plasma Na at birth (P < 0.05). Suppression of the renin activity of lambs could lead to permanent physiological changes in salt balance in later life.

Salt intake and reproductive function in sheep

Producers have the possibility to combat human-induced dryland salinity by planting salt-tolerant plants such as saltbush. Saltbush has the potential to be used as a source of food for livestock at a time and place where pasture is not viable. However, saltbush contains high concentrations of sodium chloride salt and some other anti-nutritional factors that have the potential to affect feed and water intake and, directly or indirectly, the reproductive capacity of sheep. High-salt diet during gestation induces a small modification of the activity of the renin-angiotensin system (RAS) that has an important role in the maintenance of the salt-water balance in non-pregnant and pregnant sheep. In contrast, the main effect of salt ingestion during pregnancy is observed on the biology of the offspring, with changes in the response of the RAS to salt ingestion and altered thirst threshold in response to an oral salt ingestion. These changes, observed later in life, are the result of fetal programming following the ingestion of salt by the mother. It seems that the exposure to salt during pregnancy could provide an advantage to the offspring because of this adaptive response. The response may be particularly useful, for example, when grazing herbivores are fed halophytic forages adapted to saline soils.

Fetal development and renal function in adult rats prenatally subjected to sodium overload

The aims of this study were (1) to evaluate two factors that affect fetal development--placental oxidative stress (Ox) and plasma volume (PV)--in dams with sodium overload and (2) to correlate possible alterations in these factors with subsequent modifications in the renal function of adult offspring. Wistar dams were maintained on 0.17 M NaCl instead of water from 20 days before mating until either the twentieth pregnancy day/parturition or weaning. Colorimetric methods were used to measure Ox in maternal and offspring tissues, PV, 24-h urinary protein (U(Prot24 h)) and serum triacylglycerols (TG) and cholesterol (Chol). Renal hemodynamics was evaluated in the offspring at 90 days of age using a blood pressure transducer, a flow probe and inulin clearance to measure mean arterial pressure (MAP), renal blood flow and glomerular filtration rate (GFR), respectively. The number of nephrons (NN) was counted in kidney suspensions. Dams showed unchanged PV, placental Ox and fetal weight but increased U(Prot24 h) (150%, P < 0.05). Prenatally sodium-overloaded pups showed increased U(Prot24 h) (45%, P < 0.05) but unchanged MAP, renal hemodynamics, NN and kidney Ox. Prenatally and postnatally sodium-overloaded rats showed increased U(Prot24 h) (27%, P < 0.05) and kidney Ox (44%, P < 0.05), reduced GFR (12%, P < 0.05), increased PV (26%, P < 0.05) and unchanged MAP and NN. The TG increased in both groups of treated offspring (21%, P < 0.05), whereas Chol increased only in the postnatally sodium-overloaded group. We conclude that salt overload from the prenatal stage until weaning leads to alterations in lipid metabolism and in the renal function of the pups, which are additional to those alterations seen in rats only overloaded prenatally.

Hydration in children

Water supply is a basic public problem. In modern science, three periods with different approaches to define recommended water intake in adults can be distinguished. Pediatricians agree that hydration in children may be optimal only in breastfed infants. More data are required on the health effects of different hydration states and varying water intakes in particular age and gender groups to define optimal ranges of water intake. The fetus grows in an exceptionally well-hydrated environment. Water metabolism shows several peculiarities in preterm and term infants. Infant diarrhea remains a major topic of basic and clinical research. Water intoxication in infants, toddlers, and children is rare and can only be found in exceptional circumstances. Hydration status characterized by hyponatremia may play a role in the pathogenesis of febrile convulsions in toddlers. There is increasing indirect evidence that spontaneous drinking behavior of a population may be fixed and anchored in the age range of toddlers. Sex differences in hydration status are common, but not obligatory. What causes theses differences? What is behind the various circadian rhythms of urine osmolality in children? At what age and in what quantities can alcohol and caffeine consumption be tolerated? How can individual susceptibility be defined? Reflecting on the modern epidemic of obesity in children and adolescents, a public consensus concerning use and misuse of sweetened drinks seems mandatory. Dietary reference intakes of water refer to 24-hour intake. In nutritional counselling, food and meal-based dietary advice is primarily given. Young parents are confronted with a flood of advice of varying quality. Recommendations on fluid consumption should be collated and revised.

Aquaporin-2 water channel in developing quail kidney: possible role in programming adult fluid homeostasis

Avian kidneys have loopless and looped nephrons; a countercurrent multiplier mechanism operates in the latter by NaCl recycling. We identified an aquaporin-2 (AQP2) homolog in apical/subapical regions of cortical and medullary collecting duct (CD) cells in kidneys of Japanese quail (q), Coturnix japonica. We investigated whether undernutrition during the embryonic/maturation period retards kidney and AQP2 development in quail and programs impaired volume regulation in adults. Protocols included 1) time course and 2) effects of 5-10% egg white withdrawal (EwW) or 48-h post-hatch food deprivation (FD) on nephron growth and qAQP2 mRNA expression, and 3) effects of EwW and FD on qAQP2 mRNA responses to 72-h water deprivation in adults. In metanephric kidneys, qAQP2 mRNA is expressed in medullary CDs at embryonic day 10; distribution and intensity increase during maturation. The number and size of glomeruli continue to increase after birth, whereas nephrogenic zones decrease. In EwW embryos, qAQP2 mRNA expression is initially delayed, then restored; birth weight and hatching rate are lower than in controls. Adults from EwW embryos and FD chicks have fewer (P < 0.01) glomeruli. Water deprivation reduces body weight more in EwW birds than in controls. The results suggest that qAQP2 evolved in metanephric kidneys and that undernutrition may retard nephrogenesis, leading to impaired adult water homeostasis.

Hypertension caused by prenatal testosterone excess in female sheep

Polycystic ovary syndrome (PCOS), a leading cause of infertility, affects approximately 10% of women of reproductive age. The etiology and pathophysiology of PCOS are poorly understood. PCOS is multifaceted and includes reproductive abnormalities and components of the metabolic syndrome such as insulin resistance, obesity, dyslipidemia, and hypertension. Exposure to excess testosterone (T) during the prenatal period may predispose individuals to PCOS phenotype. The goal of this study was to determine whether hypertension and dyslipidemia occur in a well-characterized model of PCOS produced by prenatal treatment of sheep with T. Radiotelemetry was used to measure blood pressure over a 24-h period in conscious, undisturbed animals. To normalize circulating estradiol levels across treatment, control (n = 4) and prenatal T-treated (100 mg T propionate im twice weekly from days 30 to 90 of fetal life, n = 4) 2-yr-old females were ovariectomized, instrumented with a radiotelemetry transmitter, and clamped with early follicular phase levels of estrogen using an implant. Six days later, a 24-h recording period commenced. Prenatal T-treated sheep were hypertensive compared with control sheep, and heart rate tended to be higher. T-treated sheep had hyperglycemia, insulin resistance, hypernatremia, and hyperchloremia, and both total and LDL cholesterol tended to be higher. Plasma aldosterone and epinephrine were significantly lower in T-treated sheep, whereas norepinephrine was unchanged. This first-ever use of radiotelemetric blood pressure recordings in sheep demonstrates that mild hypertension, a risk factor reported in some women with PCOS, is also a feature of the sheep model of PCOS produced by prenatal T treatment.

Enhanced nephrogenesis in offspring of water-restricted rat dams

OBJECTIVE

Maternal water restriction (WR) may induce offspring plasma hypertonicity and enhanced vasopressin secretory responses. We determined effects of pregnancy WR on offspring body composition, renal morphology, and blood pressure.

STUDY DESIGN

Pregnant Sprague Dawley rats (n = 21) were randomized to WR, pair-fed (PF), and control from embryo day (e) 10 to e21. Offspring body and organ weights and glomerular number and size were measured at birth and at 21 days of age. At 6 and 9 weeks, offspring blood pressure was determined.

RESULTS

At 21 days of age, WR offspring glomerular number was increased (17%; P < .05), whereas PF glomerular number was lower (4%), compared with controls. Systolic blood pressures were elevated in both WR and PF at both 6 and 9 weeks.

CONCLUSIONS

Pregnancy WR stimulates offspring nephrogenesis, suggesting an adaptive response to future dehydration. Programmed hypertension in WR and PF groups likely occurs via different mechanisms.

Gender specificity of programmed plasma hypertonicity and hemoconcentration in adult offspring of water-restricted rat dams

OBJECTIVE

We studied the impact of maternal water-restriction during rat pregnancy on newborn plasma composition, and determined the persistence of plasma composition alterations in adult offspring.

METHODS

Maternal dams were water-restricted from 10 days of pregnancy until term (21 days) and throughout lactation to increase plasma sodium levels by approximately 6 mEq/L. At 21 days of age, offspring were weaned, and subsequently maintained on ad libitum food and water until 12 weeks of age. Daily water and food intake was monitored. Blood samples and organs were collected from 1-day- and 12-week-old offspring. Hematocrit, plasma osmolality, sodium, and arginine vasopressin (AVP) levels were analyzed. Because water-restriction led to concomitant reduction in maternal food intake (ie, dehydration anorexia), henceforth these dams and their offspring are referred to as "water-deprived/food-reduced" rats.

RESULTS

Water-deprived/food-reduced dams had significantly increased plasma sodium levels, reduced food intake, and lower body weight gain during pregnancy and lactation as compared to control dams. One-day-old newborns of water-deprived/food-reduced dams weighed 17% less and had increased plasma sodium levels, osmolality, and hematocrit. At 12 weeks of age, males exhibited 11% and females 19% reduction in body weight from controls. Notably, male offspring of water-deprived/food-reduced dams showed significantly elevated plasma sodium levels, osmolality, and hematocrit. Additionally, males demonstrated reduced adrenal growth and decreased water intake. Conversely, the female offspring had similar plasma osmolality with decreased sodium levels, though a persistently elevated hematocrit. No differences were evident in plasma AVP levels.

CONCLUSIONS

Maternal water deprivation/food reduction is associated with increased newborn plasma osmolality and sodium levels and long-term physiologic changes in the offspring. The gender-specificity of programmed hyperosmolality, though not hemoconcentration, implicates differing pathways/mechanisms for these phenotypic alterations. The contributions of pregnancy hypertonicity versus nutrient restriction in the mechanism for programmed offspring phenotype remain to be elucidated.

The Importance of Good Hydration for the Prevention of Chronic Diseases

There is increasing evidence that mild dehydration plays a role in the development of various morbidities. In this review, the effects of hydration status on chronic diseases are categorized according to the strength of the evidence. Positive effects of maintenance of good hydration are shown for urolithiasis (category lb evidence); constipation, exercise asthma, hypertonic dehydration in the infant, and hyperglycemia in diabetic ketoacidosis (all category IIb evidence); urinary tract infections, hypertension, fatal coronary heart disease, venous thromboembolism, and cerebral infarct (all category III evidence); and bronchopulmonary disorders (category IV evidence). For bladder and colon cancer, the evidence is inconsistent.

Protective effect of prenatal water restriction on offspring cardiovascular homeostasis in response to hemorrhage

We determined the cardiovascular and AVP responses of prenatally dehydrated (PreDehy) neonates to intravascular hemorrhage. Ewes with singleton fetuses were subjected to water restriction from 110 days of gestation to full term to achieve hypernatremia of 8–10 meq/l. Water and food were provided ad libitum to control ewes. After delivery, water and food were provided ad libitum to ewes from both groups, and newborns were allowed to nurse ad libitum. At 15 ± 2 days of age, PreDehy and control lambs were prepared with bladder and femoral catheters and studied at 25 ± 2 days of age. After a 2-h basal period, lambs were hemorrhaged to 30% of blood volume over 1 h (0.5% of blood volume/min) and monitored 1 h after hemorrhage. Neonatal arterial blood pressure was measured, and blood samples were collected. Basal plasma sodium levels, plasma osmolality, hematocrit, and mean arterial pressure were increased in PreDehy lambs compared with controls. Both groups had similar basal AVP levels and heart rate. In response to hemorrhage, all parameters remained significantly elevated in PreDehy lambs. Blood pressure decreased less in PreDehy lambs than in controls. The hemorrhage-AVP threshold (percent blood volume withdrawal at which plasma AVP values significantly increased) was markedly elevated (20 vs. 15%) and peak hemorrhage-induced AVP plasma levels were lower (5.6 ± 1.5 vs. 10.1 ± 1.5 pg/ml, P < 0.01) in PreDehy lambs than in controls. Thus offspring of dehydrated ewes demonstrate enhanced AVP secretory responses to hypotension. Despite potential long-term adverse effects of systemic hypertension, these results suggest a protective effect of prenatal water restriction on offspring cardiovascular homeostasis during blood volume reduction.

Programmed syndrome of hypernatremic hypertension in ovine twin lambs

OBJECTIVE

An increased risk of adult hypertension, obesity, and coronary heart disease occurs in low birth weight or intrauterine growth-restricted newborn infants as a result of fetal programming. Human twins represent a natural model of low birth weight and intrauterine growth restriction because they are significantly smaller at birth than singleton infants because of both earlier delivery and reduced intrauterine growth. Increased blood pressure has been reported in several epidemiologic studies of human twin offspring, although this has not been confirmed in an animal model. Because the sheep pregnancy consists of singleton and twin litters, we sought to determine the impact of ovine twin gestation and twin nursing on the cardiovascular and renal function of the offspring.

STUDY DESIGN

Newborn lambs (n = 12) were studied at 21 +/- 2 day of life. Both singleton (n = 6) and twin lambs (n = 6) were born to ewes provided ad libitum water and food throughout gestation. After the delivery, ewes were provided ad libitum water and food, and newborn lambs were allowed ad libitum nursing with the maternal ewe. At 15 +/- 2 days of age, the lambs were prepared with vascular and renal catheters and studied at 21 +/- 2 days. After a 2-hour basal period, lambs received an intravenous infusion of hypotonic (0.075 mol/L) NaCl (0.15 ml/kg/hr) for an additional 2 hours. Newborn arterial blood pressure, heart rate, and urine flow were monitored continuously, and arterial blood samples were obtained before, during, and after the infusion.

RESULTS

At birth, twin lambs weighed 30% less than singleton lambs (3.5 +/- 0.1 kg vs 5.0 +/- 0.2 kg; P < .05), although 50% less at 21 days (5.2 +/- 0.6 vs 10.8 +/- 1.2 kg). There were marked differences in basal arterial blood values between twin and singleton lambs at 21 days, with twins having significantly increased plasma sodium and systolic, diastolic, and mean arterial pressures and reduced glomerular filtration rates, urine osmolality, osmolar excretion, and osmolar clearance (per kg body weight) compared with singleton lambs. In response to hypotonic saline solution infusion, the plasma composition and blood pressure differences between twin and singleton lambs persisted.

CONCLUSION

These results indicate that ovine twin gestation and nursing markedly reduced body weight at 21 days of age, with evidence of plasma hypernatremia, hypertension, and reduced glomerular filtration rates, which persisted throughout hypotonic saline solution infusion. Consistent with epidemiologic studies of humans, these results demonstrate that gestational/newborn nutrient stress may program hypertension in offspring.

Maternal nutrient restriction in sheep: hypertension and decreased nephron number in offspring at 9 months of age

Pregnant ewes were fed either a 50% nutrient-restricted (NR; n= 8) or a control 100% (C; n= 8) diet from day 28 to day 78 of gestation (dGA; term = 150 dGA). Lambs were born naturally, and fed to appetite throughout the study period. At 245 +/- 1 days postnatal age (DPNA), offspring were instrumented for blood pressure measurements, with tissue collection at 270 DPNA. Protein expression was assessed using Western blot, glomerulus number determined via acid maceration and hormone changes by radioimmunoassay (RIA) or enzyme-linked immunosorbent assay (ELISA). NR lambs had higher mean arterial pressure (MAP; 89.0 +/- 6.6 versus 73.4 +/- 1.6 mmHg; P < 0.05), fewer renal glomeruli (57.8 +/- 23.8 versus 64.6 +/- 19.3 x 10(4); P < 0.05), increased expression of angiotensin converting enzyme (ACE) in the renal cortex (942 +/- 130 versus 464 +/- 60 arbitrary pixel units (apu); P < 0.03), and increased angiotensin II receptor AT2 expression in the renal medulla (63.3 +/- 12.1 versus 19.5 +/- 44.2 x 10(4) apu; P < 0.03). All data are presented as mean +/-S.E.M. The present data indicate that global maternal nutrient restriction (50%) during early to mid-gestation impairs renal nephrogenesis, increases MAP, and alters expression of AT2 and ACE without an associated change in birth weight. These data demonstrate the existence of a critical window of fetal susceptibility during early to mid-gestation that alters kidney development and blood pressure regulation in later life.

Gestational programming: population survival effects of drought and famine during pregnancy

The process whereby a stimulus or stress at a critical or sensitive period of development has long-term effects is termed "programming." Studies in humans and animals convincingly demonstrate that environmental perturbations in utero may permanently change organ structure and metabolism and/or alter homeostatic regulatory mechanisms among the offspring. These programmed changes may be the origins of adult diseases, including cardiovascular disease, obesity, and diabetes. Throughout evolution and development, humans and animals have been exposed to two common environmental stresses, drought and famine. Notably, drought-induced water deprivation is associated with dehydration anorexia and thus a concomitant potential nutrient stress. Our laboratory has performed studies among pregnant rat and sheep in which we simulate drought conditions via maternal dehydration and famine conditions via nutrient restriction. Maternal dehydration results in low-birth-weight offspring, which demonstrate gender-specific plasma hypernatremia and hypertonicity and arterial hypertension. Gestational nutrient restriction also resulted in low-birth-weight offspring. If permitted rapid catch-up growth by nutrient availability, these offspring demonstrate evidence of increased body weight and body fat, and leptin resistance as adults. Conversely, if the catch-up growth is delayed by nutrition restriction, the offspring exhibit normal body weight, body fat, and plasma leptin levels as adults. These studies indicate that osmoregulatory and cardiovascular homeostasis and phenotypic predisposition to obesity may be programmed in utero. Importantly, these results suggest that programming effects may be either potentiated or prevented by interventions during the neonatal period.

Prenatal programming of hypernatremia and hypertension in neonatal lambs

Maternal water restriction and the accompanying dehydration-induced anorexia may induce long-term physiological changes in offspring. We determined the impact of prenatal hypertonicity (Pre-Dehy) on offspring cardiovascular and osmoregulatory function. Pre-Dehy lambs were exposed to in utero hypernatremia (8- to 10-meq increase; 110–150 days of gestation) induced by maternal water restriction. Control lambs were born to ewes provided ad libitum water and food throughout gestation. After delivery, all ewes were provided ad libitum water and all newborns were allowed ad libitum nursing. Lambs were prepared with vascular and bladder catheters at 15 ± 2 days of age and studied at 21 ± 2 days. After a 2-h basal period, lambs received an infusion of hypotonic (0.075 M) NaCl (0.15 ml·kg−1·h−1 iv) for 2 h. Lamb arterial blood pressure was monitored, and blood samples were obtained before, during, and after infusion. During the neonatal basal period, Pre-Dehy lambs had significantly increased plasma osmolality (302 ± 1 vs. 294 ± 1 mosmol/kgH2O, P < 0.01), sodium levels (144 ± 1 vs. 140 ± 1 meq/l, P < 0.01), hematocrit (28 ± 1% vs. 25 ± 1%, P < 0.05), and mean arterial blood pressure (79 ± 2 vs. 68 ± 1 mmHg, P < 0.001) compared with control lambs. Despite the infusion of hypotonic saline, Pre-Dehy lambs maintained relative hypertonicity, hypernatremia, and hypertension. However, plasma arginine vasopressin, glomerular filtration rate, and urinary osmolar and sodium excretion and clearance (per kg body wt) were similar in the groups. Offspring of prenatally water-restricted ewes exhibit hypernatremia, hypertonicity, and hypertension, which persist despite hypotonic saline infusion. In utero hypertonicity and perhaps maternal nutrient stress may program offspring osmoregulation and systemic arterial hypertension.