Gestational Undernutrition Research Articles

Metabolic Programming: Origin of Non-Communicable Diseases in Early Life Nutrition

Metabolic programming (MP) is defined the induction, deletion, or impaired development of a somatic structure or “setting” of a physiological system by an early life stimulus. Epidemiological and animal studies support the theory that suboptimal intrauterine conditions are associated with non-communicable disease (NCD) in adulthood. Using ovine models, we investigated the long-term consequences of late gestation undernutrition on glucose–insulin axis function and energy metabolism. We found that early life undernutrition had life-lasting consequences on insulin-secretory and adipose lipolytic capacity as well as intermediary metabolism later in life. Furthermore, we showed that suboptimal intrauterine nutrition impairs energy expenditure (EE) in gestation, apparently via an increase in the energy cost of conceptus development. Our findings, and those of other studies, support the hypothesis that energy balance is, to a certain extent, programmed early in life, presumably through appetite, EE, physical activity, and/or disproportional postnatal growth programming. Implication for health policy/practice/research/medical education:Metabolic programming is an emerging area of science dealing with the origins of non-communicable diseases. Impaired development due to suboptimal intrauterine conditions may cause short term as well as long term effects on the function of the organisms subsequently determining the health and disease in later life. Reading this review article is recommended to all family physicians, epidemiologists, nutritionists, animal scientist, endocrinologists and health policy makers. Please cite this paper as:Kiani A, Nielsen MO. Metabolic Programming: Origin of Non-Communicable Diseases in Early Life Nutrition. Int J Endocrinol Metab. 2011;9(3):409-15.DOI: 10.5812/Kowsar.1726913X.3366 Copyright © 2011 Kowsar M.P.Co. All rights reserved.  

Gestational nutrition and the development of obesity during adulthood

Recent epidemiological studies indicate a strong link between intrauterine under-nutrition and propensity of such offspring for developing obesity and metabolic syndrome in later life. Garg et al investigated the mechanistic basis of this phenomenon and its potential reversibility in rats. The authors found that rats experiencing gestational under-nutrition but fed normally after birth (IUGR) gained body mass with excessive subcutaneous and visceral fat. The IUGR rats were also metabolically inflexible since they showed similar rates of energy expenditure and O(2) consumption in the fed and fasted states. However, if such pups were food-restricted during lactation (PNGR), their metabolic profiles resembled those of control and IPGR (subject to food restriction during pre- and postnatal periods) rats. Thus, postnatal caloric restriction superimposed on intrauterine under nutrition significantly improved insulin sensitivity and adiposity of rats that would otherwise develop metabolic inflexibility and visceral obesity. The observations of Garg et al, have serious implications in term of the design of the future experimental studies as well as their clinical translation in humans.

The effect of gestational undernutrition on maternal weight change and fetal weight in lines of mice selected for different growth characteristics

The present study investigated whether the genetic growth characteristics (fast or slow growing, lean or fat) of a mother influences her ability to partition nutrients to developing offspring. A total of sixty-one pregnant mice of three selected lines were used: fast-growing, relatively fat (FF, n 19); fast-growing, relatively lean (FL, n 23); and normal growth, relatively lean (NL, n 19). On day 1 of pregnancy, mice were given either ad libitum access to food (control (C): n 32) or pair-fed at 80% of C intake (restricted (R): n 29). Feed intake and dam weight were measured daily. The weight of the mouse, organs, mammary tissue and the weight of fetuses and placentas were determined at day 18 of gestation. Overall, R dams gained less than half the weight of C dams during gestation. NL dams gained the most weight, and FF dams gained the least weight (P<0·001). R dams in the fast-growing lines mobilised significantly more body fat during gestation than the NL line (P<0·001) and had a greater reduction in mammary tissue growth. The relative weight of the litter increased in R dams of the FF line but was reduced in both the lean lines. Undernutrition reduced fetal and placental weight, and reduced placental efficiency in all the lines. The reduction was least in the FF line and greatest in the FL line. The data suggest that selection of animals for different growth characteristics alters their response to undernutrition during pregnancy, the relatively fat line was better able to buffer its offspring from the effects of undernutrition than the lean lines, regardless of their underlying rate of growth.

Prenatal famine exposure and cognition at age 59 years

Despite the perceived importance of early life nutrition for mental development, few studies have related gestational undernutrition to later-life cognitive functioning. We investigated the consequences of gestational exposure to the Dutch famine of 1944-45 for cognitive functioning at the age of 59 years. We recruited men and women who were (i) born in birth clinics in Amsterdam, Rotterdam and Leiden, between January 1945 and March 1946, whose mothers experienced famine during or immediately preceding pregnancy (n = 354); (ii) born in the same three institutions during 1943 and 1947, whose mothers did not experience famine during this pregnancy (n = 292); or (iii) same-sex siblings of those in the first two categories (n = 311). We assessed cognitive performance at the age of 59 years by means of a comprehensive test battery. All cognitive functioning test scores were within normal ranges for this age group. There were no differences in cognitive performance at the age of 59 years between individuals exposed to gestational undernutrition and those without this exposure. For the general cognitive index, a summary measure across six functional domains (mean 100, standard deviation (SD) 15 points), famine exposure was associated with a decrease of 0.57 points [95% confidence interval (95% CI) -2.41 to 1.28] points. Individuals exposed to famine in gestational weeks 1-10 had a cognitive functioning index 4.36 (95% CI 8.04-0.67) points lower than those without this exposure. Within-sibling-pair analyses gave consistent results. We found no overall association between maternal exposure to acute famine in pregnancy and cognitive performance of the offspring at the age of 59 years, but cannot rule out an association specific to early pregnancy exposure.

Maternal malnutrition and placental insufficiency induce global downregulation of gene expression in fetal kidneys.

Malnutrition during pregnancy causes intrauterine growth restriction and long-term changes in the offspring's physiology and metabolism. To explore molecular mechanisms by which the intrauterine environment conveys programming in fetal kidneys, an organ known to undergo substantial changes in many animal models of late gestational undernutrition, we used a microswine model of maternal protein restriction (MPR) in which sows were exposed to isocaloric low protein (LP) diet during late gestation/early lactation to encompass the bulk of nephrogenesis. To define general v. model-specific effects, we also used a sheep model of placental insufficiency. In kidneys from near-term fetal and neonatal microswine LP offspring, per cell levels of total RNA, poly(A)+ mRNA and transcripts of several randomly chosen housekeeping genes were significantly reduced compared to controls. Microarray analysis revealed only a few MPR-resistant genes that escape such downregulation. The ratio of histone modifications H3K4m3/H3K9m3 (active/silenced) was reduced at promoters of downregulated but not MPR-resistant genes suggesting that transcriptional suppression is the point of control. In juvenile offspring, on a normal diet from weaning, cellular RNA levels and histone mark patterns were recovered to near control levels, indicating that global repression of transcription is dependent on ongoing MPR. Importantly, cellular RNA content was also reduced in ovine fetal kidneys during placental insufficiency. These studies show that global repression of transcription may be a universal consequence of a poor intrauterine environment that contributes to fetal restriction.

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

Birth weight in humans has been inversely associated with adult disease risk. Results of animal studies have varied depending on species, strain, and treatment. 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. 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. 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.

Sex‐ and age‐specific effects of nutrition in early gestation and early postnatal life on hypothalamo‐pituitary‐adrenal axis and sympathoadrenal function in adult sheep

The early-life environment affects risk of later metabolic disease, including glucose intolerance, insulin resistance and obesity. Changes in hypothalamo-pituitary-adrenal (HPA) axis and sympathoadrenal function may underlie these disorders. To determine consequences of undernutrition in early gestation and/or immediately following weaning on HPA axis and sympathoadrenal function, 2- to 3-year-old Welsh Mountain ewes received 100% (C, n = 39) or 50% nutritional requirements (U, n = 41) from 1-31 days gestation, and 100% thereafter. From weaning (12 weeks) to 25 weeks of age, male and female offspring were then either fed ad libitum (CC, n = 22; UC, n = 19) or were undernourished (CU, n = 17; UU, n = 22) such that body weight was reduced to 85% of their individual target, based on a growth trajectory calculated from weights taken between birth and 12 weeks. From 25 weeks, ad libitum feeding was restored for all offspring. At 1.5 and 2.5 years, adrenocorticotropic hormone (ACTH) and cortisol concentrations were measured at baseline and in response to corticotropin-releasing factor (CRF) (0.5 microg kg(1)) plus arginine vasopressin (AVP) (0.1 microg kg(1)). At 2.5 years, HPA axis and sympathoadrenal (catecholamine) responses to a transport and isolation stress test were also measured. In females, post-weaning undernutrition reduced pituitary output (ACTH) but increased adrenocortical responsiveness (cortisol:ACTH area under curve) during CRF/AVP challenge at 1.5 years and increased adrenomedullary output (adrenaline) to stress at 2.5 years. In males, cortisol responses to stress at 2.5 years were reduced in those with slower growth rates from 12 to 25 weeks. Early gestation undernutrition was associated with increased adrenocortical output in 2.5-year-old females only. Pituitary and adrenal responses were also related to adult body composition. Thus, poor growth in the post-weaning period induced by nutrient restriction has sex- and age-specific effects on HPA and sympathoadrenal function. With altered glucose tolerance previously reported in this model, this may have long-term detrimental effects on metabolic homeostasis and cardiovascular function.

Changed mitochondrial function by pre- and/or postpartum diet alterations in sheep

In a sheep model, we investigated diet effects on skeletal muscle mitochondria to look for fetal programming. During pregnancy, ewes were fed normally (N) or were 50% food restricted (L) during the last trimester, and lambs born to these ewes received a normal (N) or a high-fat diet (H) for the first 6 mo of life. We examined mitochondrial function in permeabilized muscle fibers from the lambs at 6 mo of age (adolescence) and after 24 mo of age (adulthood). The postpartum H diet for the lambs induced an approximately 30% increase (P < 0.05) of mitochondrial VO(2max) and an approximately 50% increase (P < 0.05) of the respiratory coupling ratio (RCR) combined with lower levels of UCP3 and PGC-1alpha mRNA levels (P < 0.05). These effects proved to be reversible by a normal diet from 6 to 24 mo of age. However, at 24 mo, a long-term effect of the maternal gestational diet restriction (fetal programming) became evident as a lower VO(2max) (approximately 40%, P < 0.05), a lower state 4 respiration (approximately 40%, P < 0.05), and lower RCR ( approximately 15%, P < 0.05). Both PGC-1alpha and UCP3 mRNA levels were increased (P < 0.05). Two analyzed muscles were affected differently, and muscle rich in type I fibers was more susceptible to fetal programming. We conclude that fetal programming, seen as a reduced VO(2max) in adulthood, results from gestational undernutrition. Postnatal high-fat diet results in a pronounced RCR and VO(2max) increase in adolescence. However, these effects are reversible by diet correction and are not maintained in adulthood.

The impact of maternal high fat nutrition on the next generation: food for thought?

The adverse impact of maternal gestational undernutrition on the development and long-term health of offspring has now been studied extensively, both in humans and animal models, with a range of reported postnatal consequences including increased risk of cardiovascular disease and type II diabetes, as well as behavioural alterations. However, the increasing prevalence of obesity both in Western and rapidly developing societies raises the question of whether maternal overnutrition may hold similar risks for the developing fetus and its future health. Howie and colleagues (2009) reported recently in The Journal of Physiology that a high fat (HF) diet fed to female rats either throughout life, including pregnancy and lactation, or solely during pregnancy and lactation, resulted in significant changes in offspring phenotype. These included altered birth weight and postnatal growth, increased fat deposition, and changes in leptin and insulin homeostasis. Importantly, their study has shown for the first time that a HF diet consumed solely during pregnancy and lactation was equally as detrimental to the development of offspring as if the mother had experienced a life-long overconsumption of fat (Howie et al. 2009), emphasising the particular importance of maternal diet during pregnancy.

Effects of early gestational undernutrition on fetal growth, organ development, and placentomal composition in the bovine1

Fetal intrauterine growth restriction (IUGR) is known to negatively affect offspring health postnatally. This study evaluated the impacts of early gestational undernutrition followed by realimentation on bovine fetal and placental growth. Thirty multiparous beef cows bred to a single sire and gestating female fetuses were fed to meet NRC recommendations (control; n = 15) or fed below NRC recommendations (68.1% of NE(m) and 86.7% of MP recommendations; nutrient restricted, NR; n = 15) from d 30 to 125 of gestation. On d 125 of gestation, 10 control and 10 NR cows were necropsied. The remaining 5 NR cows were realimented to achieve similar BW and BCS with the remaining 5 control cows by d 190 of gestation; both groups were necropsied at d 245 of gestation. Fetal weight at d 125 of gestation was 948 +/- 14 g (n = 10) for control cows; however, fetal weights of NR cows fell into 2 distinct groups: NR non-IUGR cows had fetal weights similar to control cows (974 +/- 20 g, n = 6), whereas fetal weights of NR IUGR cows were reduced (773 +/- 23 g, n = 4; P < 0.01). Fetal brain weight as a percentage of fetal weight was increased (approximately 11%; P < 0.01) in the NR IUGR fetuses compared with fetuses from the other 2 groups, which were similar. Fetal heart weight as a percentage of fetal weight also tended to be increased (approximately 10%; P = 0.08) in NR IUGR fetuses compared with control fetuses. Nutrient-restricted IUGR cows exhibited reduced (P < 0.01) cotyledonary weights compared with NR non-IUGR and control cows, which were similar (192 +/- 27 vs. 309 +/- 22, and 337 +/- 17 g, respectively). Total placentome surface area also tended to be reduced (P = 0.07) in NR IUGR cows compared with NR non-IUGR and control cows, which again were similar (685.0 +/- 45.6 vs. 828.7 +/- 37.2 and 790.7 +/- 28.9 mm(2), respectively). On d 245 of gestation, fetal weights and caruncle weight were similar for NR and control cows; cotyledonary weights, however, were reduced in NR vs. control cows (1,430 +/- 133 vs. 2,137 +/- 133 g, P < 0.01). Decreased fetal growth in NR IUGR cows on d 125 of gestation was associated with decreased cotyledonary weights and reduced placentomal surface areas. The return of NR cows to a BW and BCS similar to that of control cows through realimentation beginning on d 126 resulted in similar fetal weights of NR and control cows by d 245 of gestation. Thus, a bout of fetal IUGR may go undetected if cows undernourished during early gestation receive feed supplementation in the second half of gestation to assure normal birth weight.

Peri‐implantation and late gestation maternal undernutrition differentially affect fetal sheep skeletal muscle development

Poor prenatal nutrition is associated with a greater risk of adult glucose intolerance and insulin insensitivity in the offspring. Skeletal muscle is the primary tissue for glucose utilization, and insulin resistance in muscle is the earliest identifiable abnormality in the pre-diabetic patient. We investigated the effect of early and late gestation undernutrition on structure and markers of growth and glucose metabolism regulation in the fetal triceps brachii (TB, slow- and fast-twitch myofibres) and soleus (slow-twitch myofibres) muscles. Pregnant sheep were fed 100% nutrient requirements (C, n = 8) or a restricted diet peri-implantation (PI, n = 9; 40%, 1-31 days gestation (dGA) (term approximately 147)) or in late gestation (L, n = 6; 50%, 104-127 dGA). At 127 +/- 1 dGA we measured myofibre and capillary density in the fetal TB and soleus muscles, and mRNA levels in the TB of insulin receptor (InsR), glucose transporter-4 (GLUT-4) and type 1 insulin-like growth factor receptor (IGF-1R). Total myofibre and capillary densities were lower in the TB, but not the soleus, of PI and L fetuses. The predominant effect in the L group was on slow-twitch myofibres. In TB, InsR, GLUT-4 and IGF-1R mRNA levels were greater in L group fetuses. Our finding of reduced myofibre density is consistent with a redistribution of resources at the expense of specific peripheral tissues by early and late gestation undernutrition which may be mediated by a decrease in capillary density. The increase in key regulatory components of glucose uptake following late gestation undernutrition may constitute a short-term compensation to maintain glucose homeostasis in the face of fewer type I (insulin-sensitive) myofibres. However, together these adaptations may influence the risk of later metabolic disease and thus our findings have implications for future strategies aimed at improving maternal diet.

Fetal Mechanisms That Lead to Later Hypertension

Extensive epidemiological and experimental evidence suggests the nutritional environment in which a developing conceptus is exposed is a major factor determining later cardiovascular disease. In this review a consideration of the extent to which altered maternal/fetal nutritional environments may predispose toward later anomalies in blood pressure control and hypertension will be undertaken. In particular, a focus will be on potentially novel mechanistic pathways through which early-mid gestational undernutrition may impact upon fetal/adult adipocyte, renal and brain function, that act to increase the risk of later hypertension developing. Within the review we shall also present an opinion on the differing animal models that are currently employed to address developmental programming and introduce a conceptual framework that synthesises current available evidence.

Effect of early gestational undernutrition on angiogenic factor expression and vascularity in the bovine placentome

The effect of early gestation maternal undernutrition followed by realimentation on placentomal vascular growth and angiogenic factor expression was determined in multiparous beef cows bred to the same bull. Cows gestating only female fetuses (n = 30) were fed in equal numbers to meet the NRC requirements (control) or were fed below the NRC requirements to lose BW (nutrient restricted; NR) from d 30 to 125 of gestation. After slaughter on d 125 of gestation, 10 control and 10 NR cows were necropsied. The remaining NR cows (n = 5) were then fed to achieve a BCS equal to their control group contemporaries (n = 5) by d 220 of gestation. All cows were fed the control diet from d 220 until 250 of gestation, when the remaining control and NR cows were slaughtered and necropsied. At necropsy, placentomes were fixed via perfusion of the caruncular and cotyledonary arteries to determine capillary vascular density. Cotyledonary (fetal placental) and caruncular (maternal placental) tissues also were snap-frozen in liquid nitrogen, and mRNA concentrations of vascular endothelial growth factor and its 2 specific receptors, fms-like tyrosine kinase and kinase insert domain containing receptor, as well as placental growth factor, were determined. There was no effect of diet or day of gestation on the percentage of proliferating caruncular cells. Although diet did not impact cotyledonary cellular proliferation, there was an increase (P < 0.05) in the percentage of proliferating cells on d 250 compared with d 125 of gestation. Nutrient restriction from d 30 to 125 increased (P < or = 0.10) placental mRNA concentrations of placental growth factor and fms-like tyrosine kinase; however, there was no alteration in vascularity. By d 250 of gestation, NR cows had increased (P < 0.05) caruncular capillary surface density and decreased (P < 0.05) cotyledonary capillary area density, capillary number density, and capillary surface density compared with control cows. Although nutrient restriction had little effect on placental vascularity by d 125, upon realimentation, alterations in vascularity became apparent by d 250 of gestation, suggesting a placental programming effect.

Effect of Gestational Nutrition on Vascular Integrity in the Murine Placenta

Maternal undernutrition is thought to result in smaller offspring and programme disease in later life. It is not known whether gestational nutrition affects development and functioning of placental vessels. The aim of this study was to ascertain if disturbed angiogenesis and junctional integrity were features of the labyrinthine vessels of placenta taken from transgenic Tie2-GFP mice fed either 18% (control) or 9% (low protein; MLP) casein diet.MLP animals showed a significant decrease in fetal weight at E14.5 and in placental and fetal weight at E18.5, however, maternal weight and litter size remained unaffected. Stereological analyses revealed that the fraction of components of the placenta remained similar in both study groups. There was a significant reduction in labyrinthine blood vessel length but not in luminal diameter in the E18.5 MLP group. In both MLP groups, perturbation of vascular endothelial Cadherin and β-catenin, regulators of junctional integrity, permeability and quiescence, was observed with higher percentage of vessels showing weak or no junctional immunoreactivity. The reduction in length of the labyrinthine vessels and the downregulation of the adhesion molecules suggest that gestational undernutrition causes vascular dysfunction in the murine placenta. This may play a role in the early life programming of disease risk.

Programming of glucose-insulin metabolism in adult sheep after maternal undernutrition

The present study examines the effects of late vs. early gestation undernutrition on adult glucose-insulin homeostasis in sheep and investigates whether the lower birth weight of twins alters glucose-insulin handling in adult life. Pregnant sheep were fed to requirement (100% intake) from day 0 of gestation to term [ approximately 147 days of gestation (dGA), control singles (CS) n = 5; control twins (CT) n = 5] or to 50% requirement from days 0-30 dGA [nutrient restricted during early gestation (NRE); n = 5] or day 110-term [NR during late nutrition (NRL); n = 4]. At all other times, NR sheep received 100% intake. All sheep lambed naturally; offspring were weaned at 10 wk and were reared on pasture until 1 yr of age. At this time, indwelling catheters were inserted, and 2-4 days later, basal metabolic and endocrine status and responses to an intravenous glucose tolerance test (IVGTT) and feeding were assessed. Adipose and skeletal muscle were then sampled after humane euthanasia and were analyzed for expression of insulin-signaling proteins and GLUT4. Between groups, birth weight of singletons was similar and increased relative to twins. At 1 yr of age, weights were similar between groups. The areas under the curve for glucose and insulin during the IVGTT were greater in NRL vs. other groups, indicating glucose intolerance. This was associated with reduced adipose, but not muscle, GLUT4, and increased adipose tissue mass. Adult glucose-insulin homeostasis in sheep was unaffected by fetal number. In conclusion, prenatal undernutrition, specifically during late gestation, affects adult offspring intermediary metabolism, and, in particular, glucose-insulin homeostasis.

The influence of undernutrition during gestation on skeletal muscle cellularity and on the expression of genes that control muscle growth.

We examined the effects of two levels of gestational undernutrition (50 % and 40 % of ad libitum) on postnatal growth rate, skeletal muscle cellularity and the expression of genes that control muscle growth, in the offspring at weaning. The results showed that the rat pups born to mothers fed the 50 % diet during gestation and a control diet during lactation had an increased postnatal growth rate compared with the pups fed the more restricted diet (40 % of ad libitum). Surprisingly, the growth rate of the control group (ad libitum) was intermediate between the 50 % and 40 % groups. The restricted diets did not alter the number of muscle fibres in the semitendinosus muscle of the offspring but the number of muscle nuclei was reduced by 16 % in the 40 % group compared with the control group. In the 50 % group, the lightest pups at birth (L) had elevated muscle insulin-like growth factor (IGF)-1, IGF binding protein (BP)-5 and proliferating cell nuclear antigen (PCNA) mRNA compared with the L pups from both the control and 40 % groups. The heaviest pups at birth (H) in the 50 % group had increased levels of IGFBP-4, PCNA and M-cadherin mRNA compared with both the control and 40 % groups. Levels of IGF-1 receptor, myostatin and MyoD mRNA did not correlate with postnatal growth. Both H and L pups from the 40 % group had reduced muscle IGF-1 mRNA but all other transcripts examined were similar to control levels. The results suggest that the increased postnatal growth rate, which accompanied milder fetal undernutrition (50 %), may be due to a more active local muscle IGF system and increased muscle-cell proliferation.

Maternal undernutrition throughout pregnancy increases adrenocorticotrophin receptor and steroidogenic acute regulatory protein gene expression in the adrenal gland of twin fetal sheep during late gestation

We have previously demonstrated that maternal undernutrition during either the ‘periconceptional’ (i.e. from 60 days (d) before until 7 d after mating) or ‘gestational’ periods (i.e. from 8 d after mating until the end of pregnancy) have differential effects on the subsequent development of the hypothalamo-pituitary-adrenocortical (HPA) axis and on adrenal growth and steroidogenesis in the sheep fetus during late gestation (term=147±3 d gestation). The specific mechanisms by which periconceptional or gestational undernutrition result in activation of the fetal HPA axis in late gestation are unclear. We have therefore investigated the impact of maternal nutrient restriction imposed either during the periconceptional period, or between 8 and 147 d gestation on the expression of specific genes in the fetal pituitary and adrenal which regulate adrenal steroidogenesis in late gestation. Ewes were maintained on either a Control (C) or Restricted (R, 70% of C) diet from 60 d before until 7 d after mating (periconceptional period) and then maintained on either a Control or Restricted diet from 8 d after mating for the remainder of pregnancy (gestational period). Four nutritional treatment groups were therefore generated (C–C, C–R, R–R and R–C). Whilst periconceptional undernutrition (R–R and R–C groups) resulted in higher fetal plasma adrenocorticotrophic hormone (ACTH) at 135–146 d gestation, there was no change in the relative level of expression of the ACTH receptor (MC2R), steroidogenic acute regulatory protein (StAR) or steroidogenic enzyme mRNAs in the fetal adrenal in late gestation. Exposure to gestational undernutrition (R–R and C–R groups), however, resulted in a stimulation in the relative level of expression of MC2R mRNA ( P=0.001) and StAR mRNA ( P=0.007) in the fetal adrenal during late gestation. This study provides new insights into the potential mechanisms by which alterations of the nutrient environment of the fetus at different stages of gestation may result in differential activation of the fetal HPA axis.

Impact of maternal undernutrition during the periconceptional period, fetal number, and fetal sex on the development of the hypothalamo-pituitary adrenal axis in sheep during late gestation.

Evidence from epidemiologic, clinical, and experimental studies has shown that a suboptimal intrauterine environment during early pregnancy can alter fetal growth and gestation length and is associated with an increased prevalence of adult hypertension and cardiovascular disease. It has been postulated that maternal nutrient restriction may act to reprogram the development of the pituitary-adrenal axis, resulting in excess glucocorticoid exposure and adverse health outcomes in later life. It is unknown, however, whether maternal nutrient restriction during the periconceptional period alters the development of the fetal pituitary-adrenal axis or whether the effects of periconceptional undernutrition can be reversed by the provision of an adequate level of maternal nutrition throughout the remainder of pregnancy. We have investigated the effect of restricted periconceptional nutrition (70% of control feed allowance) from 60 days before until 7 days after mating and the effect of restricted gestational nutrition from Day 8 to 147 of gestation on the development of the fetal hypothalamo-pituitary adrenal (HPA) axis in the sheep. In these studies, we have also investigated the effects of fetal number and sex on the pituitary-adrenal responses to periconceptional and gestational undernutrition. In ewes maintained on a control diet throughout the periconceptional and gestational periods, fetal plasma ACTH concentrations were higher and the prepartum surge in cortisol occurred earlier in singletons compared with twins. Plasma ACTH concentrations were also significantly higher in male compared with female singletons, and in twin fetuses, the prepartum surge in cortisol concentrations occurred earlier in males than in females. Periconceptional undernutrition resulted in higher fetal plasma concentrations of ACTH between 110 and 145 days of gestation and a significantly greater cortisol response to a bolus dose of corticotropin-releasing hormone in twin, but not singleton, fetuses in late gestation. We have therefore demonstrated that fetal number and sex each has an impact on the timing of the prepartum activation of the HPA axis in the sheep. Restriction of the level of maternal nutrition before and in the first week of a twin pregnancy results in stimulation of the fetal pituitary-adrenal axis in late gestation, and this effect is not reversed by the provision of a maintenance control diet from the second week of pregnancy.

2 Animal models of obesity—theories of aetiology

The multiplicity of proposed mechanisms for obesity is confusing and many questions remain to be answered. A review of all the proposed mechanisms for obesity suggests that they can be placed in two groups (Table 3). The first centres on the role of the hypothalamus in the regulation of body weight. With further knowledge it may be possible to find unifying mechanisms originating in the brain for the set-point theory, the autonomic nervous system imbalance hypothesis, the thermogenesis, hyperphagia and the hyperinsulinaemia hypotheses and the gestational undernutrition hypothesis. This group of mechanisms suggests that obesity is due to altered function of central regulatory mechanisms and that the various related hypotheses are merely looking at different aspects of the same problem. The second centres on abnormalities intrinsic to the adipocyte and could link the fat cell and perinatal overnutrition theories. This group of theories suggests that an abnormality at the fat cell level, either genetic or acquired, can result in the excessive accumulation of fat. The two groups are not contradictory. The ability to develop obesity as a result of a fat cell abnormality does not negate the existence of regulatory central mechanisms since there is a finite capacity for these mechanisms to operate.

The effect of diet on food intake and adiposity in rats made obese by gestational undernutrition

Undernutrition limited to the first two weeks (trimesters) of pregnancy in rats produces a delayed-onset enhancement of body weight and food intake in male but not female offspring. Adiposity measures (fat cell size, fat pad weight and carcass lipid content) however, were enhanced only in male offspring of previously deprived mothers maintained on a high-fat diet. Previous work had shown that although these adiposity differences are enhanced by this diet, hyperphagia was eliminated when animals were switched to the high-fat diet as adults. The current study demonstrates that if offspring of deprived animals are exposed to the high-fat diet early in life, hyperphagia ensues. Adipocyte number, and circulating triglyceride levels were unaffected by our nutritional manipulation.