Evidence of progressive deterioration of renal function in rats exposed to a maternal low-protein diet in utero

Intrauterine growth retardation associated with maternal undernutrition is proposed to play a significant role in the aetiology of hypertension and CHD. Animal experiments suggest that the kidney, which is extremely vulnerable to the adverse effects of growth-retarding factors, may play an important role in the prenatal programming of hypertension. Maintenance of renal haemodynamic functions following structural impairment in fetal life is proposed to require adaptations which raise systemic blood pressure and promote a more rapid progression to renal failure. Rats were fed on diets containing 180 g casein/kg (control) or 90 g casein/kg (low protein) during pregnancy. The offspring were studied in terms of blood pressure, creatinine clearance, blood urea N, plasma and urinary albumin, renal morphometry and metabolic activity at 4, 12 and 20 weeks of age. Blood pressure was elevated at all ages in the low-protein-exposed offspring, relative to control rats. Rats (4 weeks old) exposed to the low-protein diet had smaller kidneys which were shorter and wider than those of control animals. Creatinine clearance was significantly reduced in 4-week-old rats exposed to the low-protein diet. Renal morphometry and creatinine clearance at older ages were not influenced by prenatal diet. Blood urea N, urinary output and urinary albumin excretion were, however, significantly greater in low-protein-exposed rats than in control rats at 20 weeks of age. These findings are suggestive of a progressive deterioration of renal function in hypertensive rats exposed to mild maternal protein restriction during fetal life. This is consistent with the hypothesis that adaptations to maintain renal haemodynamic functions following impairment of fetal nephrogenesis result in an accelerated progression towards glomerulosclerosis and increased intrarenal pressures mediated by rising vascular resistance.     

In utero exposure to maternal low protein diets induces hypertension in weanling rats, independently of maternal blood pressure changes

The association between maternal nutrition, fetal growth and the later development of hypertension was investigated in the rat. Animals were habituated to diets containing 18% (control) or 9% (low) protein by weight. The rats were mated and maintained on the diets until the end of pregnancy. Lactating dams were transferred onto standard chow diet. Systolic blood pressure was determined in male and female weanling offspring, using an indirect tail-cuff method. To assess the direct effects of low protein diets upon blood pressure of adult animals, a group of male and female rats were fed 18% or 9% protein for 14 days. Blood pressure was determined at the beginning and end of the feeding period. Blood pressure was additionally assessed over 14 days in pregnant rats fed control or low protein diets. Low protein diets did not alter systolic blood pressure in adult male or female rats. The blood pressures of pregnant females fed 18% or 9% protein diets did not significantly differ at any stage of pregnancy. Rats fed 9% protein diets gave birth to significantly smaller pups. Litter sizes were unaltered, and no differences in perinatal mortality were observed. Pups exposed to maternal low protein in utero had higher systolic blood pressure at the age of 4 weeks, when compared to control pups. The phenomenon was observed in both male and female offspring. Blood pressures at 4 weeks of age were strongly associated with maternal protein intake (r = -0.55). Associations were also noted between blood pressure and maternal weight at mating (r = 0.48), and weight gain in pregnancy (r = -0.30). Fetal exposure to maternal low protein diets induces hypertension in rats. The phenomenon is observed early in life and is independent of sex and the influence of maternal blood pressure. The low protein diet itself did not produce an increase in the blood pressure of adult rats.     

Fetal exposure to a maternal low-protein diet is associated with altered left ventricular pressure response to ischaemia-reperfusion injury

Rats exposed to protein restriction as fetuses develop hypertension as adults. Hypertension increases the risk of myocardial ischaemia and infarction. We investigated whether rats exposed to low-protein diets in utero are more susceptible to myocardial ischaemia-reperfusion (IR) injury. Pregnant Wistar rats were fed control or low-protein (MLP) diets throughout pregnancy. At 4 and 8 weeks postnatal age systolic blood pressure was determined in the offspring using tail-cuff plethysmography. At 6 months of age, rats were treated with saline or N-acetylcysteine (NAC) for 48 h. Rapidly excised hearts were retro-perfused (Langendorff) to assess isolated cardiac function before (baseline), during 30 min ischaemia (no coronary perfusion) and for 60 min after reinstating coronary perfusion (reperfusion). Hearts were then harvested and treated appropriately for analysis of infarct size. Exposure to the MLP diet in utero significantly increased systolic blood pressure at 4 and 8 weeks of age (6-13 mmHg increase; P < 0.001) and significantly impaired recovery of left ventricular developed pressure after ischaemia at 6 months of age in male offspring only (P < 0.003). Pre-treatment with NAC prevented this impairment of recovery in MLP male offspring and improved recovery in all females. Myocardial infarct size was not different between dietary groups after IR, but NAC pre-treatment significantly reduced the degree of infarction (P < 0.001). In conclusion, an MLP diet throughout gestation significantly impairs recovery of the 6-month-old adult rat heart to IR-induced injury in a sex-specific manner. Undernutrition during development may increase susceptibility to CHD by impairing recovery from coronary events.     

Maternal protein restriction during pregnancy and lactation in rats imprints long-term reduction in hepatic lipid content selectively in the male offspring

Maternal protein restriction during pregnancy and lactation reduces whole body lipid stores and alters lipid homeostasis in the adult offspring. Lipid homeostasis in the body is regulated, in part, by the liver via the metabolic processes of synthesis and utilization of lipids. The present study tested the hypothesis that maternal protein restriction will imprint changes in hepatic lipid metabolism and thereby alter the hepatic lipid content of the adult offspring. Pregnant rats were fed purified diets containing 19% protein (control group) or 8% protein (low-protein group) throughout pregnancy and lactation. On day 28, pups from both groups were weaned onto regular laboratory chow. On days 65 and 150, male and female pups from each litter in both groups were killed and blood and liver collected. Maternal protein restriction was found to reduce birth weight and produce long-term reduction in the body weight of the offspring. On day 65, liver triglyceride content was decreased by 40% in the male offspring that were fed a low-protein diet. The reduction in liver triglyceride content persisted until day 150, at which time it was accompanied by decreases in hepatic cholesterol content. No such changes were observed in the female offspring. To determine if the alterations in liver lipid content resulted in compensatory changes in liver carbohydrate stores, hepatic glycogen content was measured in male offspring. Hepatic glycogen content was similar between the 2 groups on days 65 and 150. In conclusion, the present study in rats showed that maternal protein restriction during pregnancy and lactation imprints long-term changes in hepatic lipid content selectively in the male offspring.     

Critical differences between two low protein diet protocols in the programming of hypertension in the rat

Maternal nutrition has been identified as a factor determining fetal growth and risk of adult disease. In rats, the feeding of a low protein diet during pregnancy retards fetal growth and induces hypertension in the resulting offspring. Rat models of low protein feeding have been extensively used to study the mechanisms that may link maternal nutrition with impaired fetal growth and later cardiovascular disease and diabetes. Low protein diets of differing composition used in different laboratories have yielded inconsistent data on the relationship between maternal protein intake and offsprings' blood pressure. Two separate low protein diet protocols were compared in terms of their ability to programme hypertension during fetal life. Pregnant rats were assigned to receive one of four diets. Two diets were obtained from a commercial supplier and provided casein at 22 or 9% by weight (H22, control; H9, low protein). The other two diets, manufactured in our own facility, provided 18% casein (S18, control) or 9% casein (S9, low protein) by weight. The diets differed principally in their overall fat content, fatty acid composition, methionine content and the source of carbohydrate. Feeding of the experimental diets commenced on the first day of pregnancy and continued until the rats delivered their litters. Following weaning all the offspring had blood pressure determined on a single occasion. Both low protein diets reduced maternal weight gain relative to their corresponding control diets. Despite this litter sizes were unaffected by the dietary protocols. Both low protein diets reduced birthweights of the pups. Systolic blood pressure was significantly elevated in the offspring of rats fed a low protein S9 diet relative to all other groups (P < 0.05). Animals exposed to H9 diet in utero had similar blood pressures to their H22 controls. It is concluded from this work that differing low protein diet manipulations in rat pregnancy elicit different programming effects upon the developing cardiovasculature. The balance of protein and other nutrients may be a critical determinant of the long-term health effects of maternal undernutrition in pregnancy.     

Taurine supplementation restored the changes in pancreatic islet mitochondria in the fetal protein-malnourished rat

Intra-uterine growth retardation has been linked to the development of type 2 diabetes in later life. Mitochondrial changes have been suggested as a link between fetal malnutrition and adult insulin resistance. Taurine has been implicated in this process. We investigated whether protein malnutrition in early life alters mitochondria of the pancreatic islets in adulthood, and whether taurine supplementation restores these changes. Male offspring of rats fed a control diet, a low-protein diet or a low-protein diet supplemented with taurine during pregnancy and lactation were weaned onto the control diet. In each group, at 20 weeks of age, intravenous glucose tolerance tests, euglycaemic-hyperinsulinaemic clamp studies, morphometric analysis of the pancreatic islets and ultra-structural analysis of the mitochondria of the β-cells were performed. The expressions of cytochrome c oxidase (COX) I and mitochondrial respiratory chain complex II were also measured. Fetal protein-malnourished rats showed decreased pancreatic islet mass and reduced insulin-secretory responses to a glucose load. These rats also showed reduced mitochondrial DNA-encoded COX I gene expression in the islets. Electron microscopic examination showed abnormal mitochondrial shapes in the β-cells of fetal protein-malnourished rats. Taurine supplementation to the low-protein diet restored all these changes. Our findings indicate that a maternal protein-restriction diet causes long-lasting mitochondrial changes that may contribute to the development of type 2 diabetes later in life. The lack of taurine may be a key causative factor for these dysfunctional mitochondrial changes.     

Maternal undernutrition programmes atherosclerosis in the ApoE*3-Leiden mouse

Poor quality of nutrition during fetal development is associated with adverse health outcomes in adult life. Epidemiological studies suggest that markers of fetal undernutrition are predictive of risk of the metabolic syndrome and CHD. Here we show that feeding a low-protein diet during pregnancy programmed the development of atherosclerosis in ApoE*3-Leiden mice. ApoE*3-Leiden mice carry a mutation of human ApoE*3 rendering them prone to atherosclerosis when fed a diet rich in cholesterol. It was noted that fetal exposure to protein restriction led to a greater degree of dyslipidaemia in mice when fed an atherogenic diet, with low-protein-exposed ApoE*3 mice having elevated total plasma cholesterol (34 % higher; P < 0.001) and TAG (39 % higher; P < 0.001) relative to offspring exposed to a control diet in utero. The low-protein group developed more severe atherosclerotic lesions within the aortic arch (2.61-fold greater lesion area; P < 0.001). Analysis of a targeted gene array suggested a potential role for members of the LDL receptor superfamily, along with similar programmed suppression of the mRNA expression of hepatic sterol regulatory element-binding protein-1c. This indicates that disordered lipid metabolism may play a role in the fetal programming of atherosclerosis in this model. Whereas earlier studies have shown early programming of cardiovascular risk factors, these results demonstrate for the first time that the interaction of prenatal undernutrition with a postnatal atherogenic diet increases the extent of atherosclerotic disease.     

Interactions between protein and vegetable oils in the maternal diet determine the programming of the insulin axis in the rat

The available evidence suggests that metabolic control mechanisms are programmed early in life. Previous studies of pregnant rats fed low-protein diets have suggested that the vegetable oils used in the experimental diets influence the outcome. The present study investigated the offspring of female rats fed semi-synthetic diets containing either 180 or 90g casein/kg with 70 g/kg (w/w) of either corn oil or soya oil during gestation. During lactation, the dams received stock diet, and the offspring were subsequently weaned onto the stock diet. The offspring of dams fed the low-protein diets were smaller at birth. At 25 weeks of age, the offspring were subjected to an oral glucose tolerance test. In the offspring of dams fed the diet containing soya oil, the area under the insulin curve was affected by the protein content of the maternal diet. There was no effect of protein on the area under the insulin curve in the offspring of dams fed the diet prepared with corn oil. There were no differences in plasma glucose concentrations. The levels of mRNA for acetyl-CoA carboxylase- in the livers of female offspring were affected by the protein and oil content of the maternal diet. The level of carnitine palmitoyl transferase mRNA was affected by the protein content of the maternal diet. The present study suggests that PUFA in the maternal diet can interact with protein metabolism to influence the development of the offspring. This may involve the higher content of alpha-linolenic acid in soya oil compared with corn oil.     

Lack of diabetogenic effect of alloxan in protein-calorie malnourished rats

Male weanling rats were fed one of three diets for 46 days. The diets were control, a 4% casein-containing and a 4% casein + 0.7% cysteine diets. On day 47, the rats were injected with alloxan (40 mg/kg body weight) via the tail vein and frequencies of alloxan-induced diabetes were appraised on days 55-57 by measurement of blood glucose, urine output, water intake and food intake. Alloxan was almost ineffective in producing diabetes in the two low-protein groups (frequencies of diabetes = 0/11 and 3/11 for the 4% casein diets without and with cysteine, respectively) but was highly effective in the control group (100% diabetogenesis). The decreased diabetogenicity of low-protein diets was not due to decreased food intake. All the animals fed control diet in amounts which matched the intake of protein-malnourished animals became diabetic when alloxan was administered. These data suggest a defect in the alloxan-glucose recognition site on beta cells of protein malnourished rats.     

Effects of geophagia (kaolin ingestion) on the maternal blood and embryonic development in the pregnant rat

Geophagia, in the form of clay-eating, is often observed during pregnancy in the human population. The intent of this study was to determine the effects of kaolin (clay) ingestion on the maternal blood and embryonic development of the pregnant rat. Thirty-six Sprague-dawley female rats were divided into three groups: control diet, 20% kaolin diet, and iron-supplemented 20% kaolin diet. The diets were fed 37 to 68 days, 69 to 95 days, and 96 to 117 days prior to fertilization, and the same diets were fed for the duration of the gestation period. The rats fed the kaolin diet exhibited significant reductions in hemoglobin, hematocrit, and red blood cell levels, thus indicating maternal anemia. There was also a significant reduction in the birth weight of the pups born to kaolin fed rats. The kaolin fed rats receiving an iron supplement maintained hematocrit, hemoglobin, red blood cell levels, and pup weight within the normal range.     

Dietary Fibre,Coronary Heart Disease and Diabetes Mellitus

Maternal nutrition has been identified as a factor determining fetal growth and risk of adult disease. In rats, the feeding of a low protein diet during pregnancy retards fetal growth and induces hypertension in the resulting offspring. Rat models of low protein feeding have been extensively used to study the mechanisms that may link maternal nutrition with impaired fetal growth and later cardiovascular disease and diabetes. Low protein diets of differing composition used in different laboratories have yielded inconsistent data on the relationship between maternal protein intake and offsprings' blood pressure. Two separate low protein diet protocols were compared in terms of their ability to programme hypertension during fetal life. Pregnant rats were assigned to receive one of four diets. Two diets were obtained from a commercial supplier and provided casein at 22 or 9% by weight (H22, control; H9, low protein). The other two diets, manufactured in our own facility, provided 18% casein (S18, control) or 9% casein (S9, low protein) by weight. The diets differed principally in their overall fat content, fatty acid composition, methionine content and the source of carbohydrate. Feeding of the experimental diets commenced on the first day of pregnancy and continued until the rats delivered their litters. Following weaning all the offspring had blood pressure determined on a single occasion. Both low protein diets reduced maternal weight gain relative to their corresponding control diets. Despite this litter sizes were unaffected by the dietary protocols. Both low protein diets reduced birthweights of the pups. Systolic blood pressure was significantly elevated in the offspring of rats fed a low protein S9 diet relative to all other groups (P < 0.05). Animals exposed to H9 diet in utero had similar blood pressures to their H22 controls. It is concluded from this work that differing low protein diet manipulations in rat pregnancy elicit different programming effects upon the developing cardiovasculature. The balance of protein and other nutrients may be a critical determinant of the long-term health effects of maternal undernutrition in pregnancy.     

Influence of dietary protein levels on beta-alanine aminotransferase expression and activity in rats.

beta-Alanine-oxoglutarate aminotransferase (beta-AlaAT I) and beta-alanine-pyruvate aminotransferase (beta-AlaAT II) catalyze the transamination reaction of omega-amino acids such as beta-alanine, beta-aminoisobutyrate, and gamma-aminobutyrate, amino acids that are not protein constituents. The influence of dietary protein levels on the expression and activities of these enzymes was investigated by using male rats. Both beta-AlaAT I and beta-AlaAT II activities in the liver were increased with the level of protein in the diet in accordance with changes in their mRNA levels. However, the beta-AlaAT I activity in the kidney was increased by protein-free and low-protein diets in relation to changes in its mRNA level. On the other hand, the level of beta-AlaAT II activity in the kidney was slightly decreased by a protein-free diet. Neither beta-AlaAT I nor beta-AlaAT II activities in the kidney were affected by a high-protein diet. These results suggested that beta-alanine may be used efficiently in animals fed a proteinfree or low-protein diet because the kidney provides beta-alanine by means of the hydrolysis of beta-alanyl-L-histidine (carnosine). The addition of beta-alanine to the diet significantly activated beta-AlaAT I in the kidneys of rats in accordance with changes in its mRNA level. In the rat brain, beta-AlaAT I activity was not altered by the dietary protein level or by the beta-alanine diet, and beta-AlaAT II activity was not detected.     

Fetal programming of cardiovascular function through exposure to maternal undernutrition

A substantial and robust body of epidemiological evidence indicates that prenatal dietary experience may be a factor determining cardiovascular disease risk. Retrospective cohort studies indicate that low birth weight and disproportion at birth are powerful predictors of later disease risk. This prenatal influence on non-communicable disease in later life has been termed programming. Maternal nutritional status has been proposed to be the major programming influence on the developing fetus. The evidence from epidemiological studies of nutrition, fetal development and birth outcome is, however, often weak and inconclusive. The validity of the nutritional programming concept is highly dependent on experimental studies in animals. The feeding of low-protein diets in rat pregnancy results in perturbations in fetal growth and dimensions at birth. The offspring of rats fed low-protein diets exhibit a number of metabolic and physiological disturbances, and are consistently found to have high blood pressure from early postnatal life. This experimental model has been used to explore potential mechanisms of programming through which maternal diet may programme the cardiovascular function of the fetus. Indications from this work are that fetal exposure to maternally-derived glucocorticoids plays a key role in the programming mechanism. Secondary to this activity, the fetal hypothalamic-pituitary-adrenal axis may stimulate renin-angiotensin system activity, resulting in increased vascular resistance and hypertension.     

Nutritional recovery with a soybean flour diet improves the insulin response to a glucose load without modifying glucose homeostasis

OBJECTIVE: We investigated the effect of nutritional recovery with a soybean flour diet on glucose tolerance, insulin response to a glucose load, and the action of insulin in adult rats exposed to a protein deficiency during intrauterine life and lactation. METHODS: Male Wistar rats from dams fed a normal- or low-protein diet during pregnancy and lactation were maintained after weaning by feeding them normal-protein isoenergetic diets containing soybean flour or casein and low-protein casein diet. RESULTS: Rats fed a soybean flour diet had a lower final body weight, epididymal fat pad, carcass fat content, and liver glycogen level. The serum glucose concentrations in the basal and fed states and the area under the glucose curves during the glucose tolerance test were not significantly different among the four groups. Their serum insulin levels during fasting were observed to be similar to those fed a casein diet. These rats also had a higher serum insulin levels in a fed state and total area under the insulin curves in response to a glucose load, but a lower ratio of area under the glucose/insulin curves during the glucose tolerance test than those fed a casein diet. CONCLUSION: These results indicate that nutritional recovery with a soybean flour diet improved the insulin response to a glucose load and decreased the sensitivity to insulin, at least in hepatic tissue.     

Effects of lead exposure before pregnancy and dietary calcium during pregnancy on fetal development and lead accumulation

Millions of women of child-bearing age have substantial bone lead stores due to lead exposure as children. Dietary calcium ingested simultaneously with lead exposure can reduce lead absorption and accumulation. However, the effects of dietary calcium on previously accumulated maternal lead stores and transfer to the fetus have not been investigated. We studied the effects of lead exposure of female rats at an early age on fetal development during a subsequent pregnancy. We gave 5-week-old female Sprague-Dawley rats lead as the acetate in their drinking water for 5 weeks; controls received equimolar sodium acetate. This was followed by a 1-month period without lead exposure before mating. We randomly assigned pregnant rats (n = 39) to diets with a deficient (0.1%) or normal (0.5%) calcium content during pregnancy. A total of 345 pups were delivered alive. Lead-exposed dams and their pups had significantly higher blood lead concentrations than controls, but the concentrations were in the range of those found in many pregnant women. Pups born to dams fed the calcium-deficient diet during pregnancy had higher blood and organ lead concentrations than pups born to dams fed the 0. 5% calcium diet. Pups born to lead-exposed dams had significantly (p<0.0001) lower mean birth weights and birth lengths than controls. There were significant inverse univariate associations between dam or pup organ lead concentrations and birth weight or length. The 0.5% calcium diet did not increase in utero growth. Stepwise regression analysis demonstrated that greater litter size and female sex were significantly associated with reduced pup birth weight and length. However, lead exposure that ended well before pregnancy was significantly (p<0.0001) associated with reduced birth weight and length, even after litter size, pup sex, and dam weight gain during pregnancy were included in the regression analysis. The data demonstrate that an increase in dietary calcium during pregnancy can reduce fetal lead accumulation but cannot prevent lead-induced decreases in birth weight and length. The results provide evidence that dietary nutrients can influence the transfer of toxins to the fetus during pregnancy. If these results are applicable to women, an increase in diet calcium during pregnancy could reduce the transfer of lead from prepregnancy maternal exposures to the fetus.     

Beneficial effect of moderate protein restriction on growth, renal function and survival in young rats with chronic renal failure

We used the model of one-stage uninephrectomy and contralateral heminephrectomy to study the effect of protein restriction on growth and renal function in young (starting age 21 d) female rats. Normal, sham-operated, pair-fed, and chronic renal insufficiency (CRI) rats were fed a 6, 14 or 22% protein (casein) diet. Diets were otherwise isoenergetic and equivalent in sodium, potassium, chloride, phosphate and calcium. Weight, length, urinary protein and creatinine clearances were measured up to 6 mo of age. Regardless of group (normal, sham or CRI), animals fed a 6% protein diet weighed less and were shorter than animals fed 14 or 22% protein diets. No difference in growth could be found between 14 and 22% protein intake. However, animals with CRI fed 22% protein diet had a shorter survival time than animals fed 14 or 6% protein diets. Six percent protein intake led to a lower growth rate over the first 10-12 wk of age than 14 or 22% protein intake. We conclude that 14% protein intake in rats with CRI maintains normal growth and improves survival over 22% protein intake. Rats with CRI fed a 6% protein diet have improved survival compared to rats fed a 22% protein diet but suffer growth retardation.     

Soybean diet alters the insulin-signaling pathway in the liver of rats recovering from early-life malnutrition

ObjectiveWe investigated if alterations in the insulin-signaling pathway could contribute to reduced hepatic glycogen levels in adult rats subjected to a protein deficiency during intrauterine life and lactation and reared through to recovery on a soybean diet.MethodsRats from mothers fed with 17% or 6% protein (casein) during pregnancy and lactation were maintained with a 17% casein diet (offspring born to and suckled by mothers fed a control diet and subsequently fed the same diet after weaning [CC group] and offspring born to and suckled by mothers fed a control diet and subsequently fed a soybean flour diet with 17% protein after weaning [CS group]), a soybean diet (offspring of mothers fed a low-protein diet and a control diet after weaning [LC group] and offspring of mothers fed a low-protein diet and fed a soybean flour diet containing 17% protein after weaning [LS group]), or a 6% casein diet (offspring of mothers fed a low-protein diet and subsequently fed the same diet after weaning [LL group]) from weaning until 90 d of life.ResultsA soybean diet did not modify basal serum glucose and glucagon concentrations, but raised basal serum insulin and consequently increased the serum insulin/glucose ratio. Insulin receptor and insulin receptor substrate-1 levels were lower in rats fed a soybean diet compared with those maintained with a casein diet. In the LS group, the p85 levels were higher than in the LC group, whereas in CS rats its expression was lower than in CC rats. The expression of p110 was lower in the CS group compared with the CC group and similar in the LS and LC groups. Insulin receptor substrate-1 phosphorylation was similar in the LS, LC, and CS groups and lower compared with the CC group. The insulin receptor substrate-1–p85/phosphatidylinositol 3-kinase association was lower in LS than in LC rats and in CS than in CC rats. Akt phosphorylation was lower in the CS and LS groups than in the CC and LC groups.ConclusionAdult rats maintained with a soybean diet exhibited insulin resistance due, at least in part, to alterations in the early steps of the insulin signal transduction pathway.     

Serum leptin and insulin levels in lactating protein-restricted rats: implications for energy balance

The present study analysed the effect of protein restriction on serum insulin and leptin levels and their relationship with energy balance during lactation. Four groups of rats received isocaloric diets containing 170 g protein/kg or 60 g protein/kg from pregnancy until the 14th day of lactation: control non-lactating, control lactating (both fed a control diet), low-protein non-lactating and low-protein lactating. Energy intake, body composition, energy balance, serum insulin and leptin concentrations and the relationship between these hormones and several factors related to obesity were analysed. Low-protein-intake lactating rats exhibited hypoinsulinaemia, hyperleptinaemia, hypophagia and decreased energy expenditure compared with control lactating rats. The protein level in the carcasses was lower in the low-protein lactating group than in the control lactating group, resulting in a higher fat content in the first group compared with the latter. Body fat correlated inversely with serum insulin and positively with serum leptin level. There was a significant negative correlation between serum leptin and energy intake, and a positive relationship between energy intake and serum insulin level in lactating rats and in the combined data from both groups. Energy expenditure was correlated positively with serum insulin and negatively with serum leptin in lactating rats and when data from control non-lactating and lactating rats were pooled. Lactating rats submitted to protein restriction, compared with lactating control rats, showed that maternal reserves were preserved owing to less severe negative energy balance. This metabolic adaptation was obtained, at least in part, by hypoinsulinaemia that resulted in increased insulin sensitivity favouring enhanced fat deposition, hyperleptinaemia and hypophagia.     

The effects of maternal protein restriction on the growth of the rat fetus and its amino acid supply.

Maternal protein deficiency causes fetal growth retardation which has been associated with the programming of adult disease. The growth of the rat fetus was examined when the mothers were fed on diets containing 180, 90 and 60 g protein/kg. The numbers of fetuses were similar in animals fed on the 180 and 90 g protein/kg diets but the number was significantly reduced in the animals fed on the 60 g protein/kg diet. The fetuses carried by the mothers fed on the 90 g protein/kg diet were 7.5% heavier than those of mothers fed on 180 g protein/kg diet on day 19 of gestation, but by day 21 the situation was reversed and the fetuses in the protein-deficient mothers were 14% smaller. Analysis of the free amino acids in the maternal serum showed that on day 19 the diets containing 90 and 60 g protein/kg led to threonine concentrations that were reduced to 46 and 20% of those found in animals fed on the control (180 g/kg) diet. The other essential amino acids were unchanged, except for a small decrease in the branched-chain amino acids in animals fed on the 60 g protein/kg diet. Both low-protein diets significantly increased the concentrations of glutamic acid+glutamine and glycine in the maternal serum. On day 21 the maternal serum threonine levels were still reduced by about one third in the group fed on the 90 g protein/kg diet. Dietary protein content had no effect on serum threonine concentrations in nonpregnant animals. Analysis of the total free amino acids in the fetuses on day 19 showed that feeding the mother on a low-protein diet did not change amino acid concentrations apart from a decrease in threonine concentrations to 45 and 26% of the control values at 90 and 60 g protein/ kg respectively. The results suggest that threonine is of particular importance to the protein-deficient mother and her fetuses. Possible mechanisms for the decrease in free threonine in both mother and fetuses and the consequences of the change in amino acid metabolism are discussed.     

Long-term programming of blood pressure by maternal dietary iron restriction in the rat

We have reported that blood pressure was elevated in 3-month-old rats whose mothers were Fe-restricted during pregnancy. These animals also had improved glucose tolerance and decreased serum triacylglycerol. The aim of the present study was to determine whether these effects of maternal nutritional restriction, present in these animals at 3 months of age, can be observed in the same animals in later life. Pulmonary and serum angiotensin converting enzyme (ACE) concentrations were also measured to investigate whether the renin-angiotensin system was involved in the elevation of blood pressure observed in the offspring of Fe-restricted dams. Systolic blood pressure was higher in the offspring of Fe-restricted dams at 16 months of age. Heart and kidney weight were increased as a proportion of body weight in the offspring of Fe-restricted dams. The pulmonary ACE concentration was not significantly different between the groups. The serum ACE concentration was significantly elevated in the offspring of Fe-restricted dams at 3 but not 14 months of age. There was a strong correlation between serum ACE levels at 3 and 14 months of age. Glucose tolerance and serum insulin were not different between the maternal diet groups. Serum triacylglycerol tended to be lower in the offspring of Fe-restricted dams. There were no differences in serum non-esterified fatty acids or serum cholesterol between the maternal diet groups. This study provides further evidence that maternal nutrition has effects on the offspring that persist throughout life. At 16 months of age, the elevation of blood pressure in Fe-restricted offspring does not appear to be mediated via changes in ACE levels. Both cardiac hypertrophy and decreased serum triacylglycerol have also been observed in Fe-restricted fetuses, suggesting that these changes may be initiated in utero.