Short-term exercise training early in life restores deficits in pancreatic β-cell mass associated with growth restriction in adult male rats

Fetal growth restriction followed by early catch-up growth impairs pancreatic islet morphology in male rats

Fetal growth restriction (FGR), followed by postnatal early catch-up growth, is associated with an increased risk of metabolic dysfunction, including type 2 diabetes in humans. This study aims to determine the effects of FGR and early catch-up growth after birth on the pathogenesis of type 2 diabetes, with particular attention to glucose tolerance, pancreatic islet morphology, and fibrosis, and to elucidate its mechanism using proteomics analysis. The FGR rat model was made by inducing mild intrauterine hypoperfusion using ameroid constrictors (ACs). On day 17 of pregnancy, ACs were affixed to the uterine and ovarian arteries bilaterally, causing a 20.9% reduction in birth weight compared to sham pups. On postnatal day 4 (P4), the pups were assigned to either the good nutrition (GN) groups with 5 pups per dam to ensure postnatal catch-up growth or poor nutrition groups with 15 pups per dam to maintain lower body weight. After weaning, all pups were fed regular chow food ad libitum (P21). Rats in both FGR groups developed glucose intolerance; however, male rats in the FGR good nutrition (FGR-GN) group also developed hypertriglyceridemia and dysmorphic pancreatic islets with fibrosis. A comprehensive and functional analysis of proteins expressed in the pancreas showed that FGR, followed by early catch-up growth, severely aggravated cell adhesion-related protein expression in male offspring. Thus, FGR and early catch-up growth caused pancreatic islet morphological abnormalities and fibrosis associated with the disturbance of cell adhesion-related protein expressions. These changes likely induce glucose intolerance and dyslipidemia in male rats.

Impacts of an Exercise Intervention on the Health of Pancreatic Beta-Cells: A Review

There is an increasing consensus that exercise is a medicine and that regular exercise can effectively improve and prevent metabolic diseases such as diabetes. Islet cells are the endocrine of the pancreas and vital to the development of diabetes. Decades of developmental research in exercise intervention and the health of islet cells confirmed that exercise exerts beneficial effects on the function, proliferation, and survival rate of islet cells. However, the precise exercise reference scheme is still elusive. To accomplish this goal, we searched and analyzed relevant articles, and concluded the precise exercise prescription treatments for various species such as humans, rats, and mice. Each exercise protocol is shown in the tables below. These exercise protocols form a rich pipeline of therapeutic development for exercise on the health of islet cells.

Maternal Hypothyroidism in Rats Reduces Placental Lactogen, Lowers Insulin Levels, and Causes Glucose Intolerance

Hypothyroidism increases the incidence of gestational diabetes mellitus (GDM) but the mechanisms responsible are unknown. This study aimed to assess the pathophysiological mechanisms by which hypothyroidism leads to glucose intolerance in pregnancy. Hypothyroidism was induced in female Sprague-Dawley rats by adding methimazole (MMI) to drinking water at moderate (MOD, MMI at 0.005% w/v) and severe (SEV, MMI at 0.02% w/v) doses from 1 week before pregnancy and throughout gestation. A nonpregnant cohort received the same dose for the same duration but were not mated. On gestational day 16 (GD16), or nonpregnant day 16 (NP16), animals were subjected to an intraperitoneal glucose tolerance test. Tissues and blood samples were collected 4 days later. Hypothyroidism induced a diabetic-like phenotype by GD16 in pregnant females only. Pregnant MOD and SEV females had reduced fasting plasma insulin, less insulin following a glucose load, and altered expression of genes involved in insulin signaling within skeletal muscle and adipose tissue. Hypothyroidism reduced rat placental lactogen concentrations, which was accompanied by reduced percentage β-cell cross-sectional area (CSA) relative to total pancreas CSA, and a reduced number of large β-cell clusters in the SEV hypothyroid group. Plasma triglycerides and free fatty acids were reduced by hypothyroidism in pregnant rats, as was the expression of genes that regulate lipid homeostasis. Hypothyroidism in pregnant rats results in a diabetic-like phenotype that is likely mediated by impaired β-cell expansion in pregnancy. This pregnancy-specific phenomenon is likely due to reduced placental lactogen secretion.

Maternal exercise alters rat fetoplacental stress response: Minimal effects of maternal growth restriction and high-fat feeding

INTRODUCTION

Fetal growth restriction complicates 10% of pregnancies and increases offspring (F1) risk of metabolic disorders, including obesity and gestational diabetes mellitus (GDM). This disease predisposition can be passed onto the next generation (F2). Importantly, the risk of pregnancy complications in obese women can be exacerbated by a stressful pregnancy. Exercise can reduce adiposity and improve health outcomes in obese women and those with GDM. This study investigated the impacts of maternal growth restriction, obesity, exercise, and stress on fetal and placental endocrine function.

METHODS

Uteroplacental insufficiency (Restricted) or sham (Control) surgery was induced on embryonic day (E) 18 in F0 Wistar-Kyoto rats. F1 offspring were fed a Chow or High-fat (HFD) diet from weaning and, at 16 weeks, were randomly allocated an exercise protocol; Sedentary, Exercised prior to and during pregnancy (Exercise), or Exercised only during pregnancy (PregEx). Females were mated and further randomly allocated to either undergo (Stress), or not undergo (Unstressed), physiological measurements during pregnancy. On E20, F2 fetal plasma (steroid hormones), tissues (brain, liver), and placentae (morphology, stress genes) were collected.

RESULTS

Maternal growth restriction and high-fat feeding had minimal impact on fetoplacental endocrine function. PregEx and Exercise increased cross-sectional labyrinth and junctional zone areas. PregEx, but not Exercise, increased fetal deoxycorticosterone concentrations and reduced placental Hsd11b2 and Nr3c2 gene abundance. Maternal stress increased fetal corticosterone concentrations in Sedentary HFD dams and increased placental cross-sectional areas in PregEx mothers.

DISCUSSION

PregEx and Stress independently dysregulates the endocrine status of the developing fetus, which may program future disease.

Maternal exercise attenuates the lower skeletal muscle glucose uptake and insulin secretion caused by paternal obesity in female adult rat offspring

KEY POINTS

Paternal obesity negatively influences metabolic outcomes in adult rat offspring. Maternal voluntary physical activity has previously been reported to improve glucose metabolism in adult rat offspring sired by healthy fathers. Here, we investigated whether a structured programme of maternal exercise training before and during gestation can attenuate the negative impacts that paternal obesity has on insulin sensitivity and secretion in female adult offspring. Exercise before and during pregnancy normalised the lower insulin sensitivity in skeletal muscle and the lower insulin secretion observed in female offspring sired by obese fathers. This paper presents a feasible, low-cost and translatable intervention strategy that can be applied perinatally to support multifactor interventions to break the cycle of metabolic dysfunction caused by paternal obesity.

ABSTRACT

We investigated whether maternal exercise before and during gestation could attenuate the negative metabolic effects of paternal high-fat diet-induced obesity in female adult rat offspring. Fathers consumed a normal chow or high-fat diet before mating. Mothers exercised on a treadmill before and during gestation or remained sedentary. In adulthood, female offspring were assessed using intraperitoneal insulin and glucose tolerance tests (IPITT and IPGTT, respectively), pancreatic morphology, ex vivo skeletal muscle insulin-stimulated glucose uptake and mitochondrial respiratory function. Paternal obesity impaired whole-body and skeletal muscle insulin sensitivity and insulin secretion in adult offspring. Maternal exercise attenuated the lower insulin-stimulated glucose uptake in offspring sired by obese fathers but distal insulin signalling components (p-AKT Thr308 and Ser473, p-TBC1D4 Thr642 and GLUT4) remained unchanged (P > 0.05). Maternal exercise increased citrate synthase activity only in offspring sired by obese fathers. Maternal exercise also reversed the lower insulin secretion in vivo observed in offspring of obese fathers, probably due to an attenuation of the decrease in pancreatic beta cell mass. In summary, maternal exercise before and during pregnancy in rats attenuated skeletal muscle insulin resistance and attenuated the decrease in pancreatic beta cell mass and insulin secretion observed in the female offspring of obese fathers.

The benefits of physical exercise for the health of the pancreatic β-cell: a review of the evidence

NEW FINDINGS

What is the topic of this review? This review discusses the evidence of the benefits of exercise training for β-cell health through improvements in function, proliferation and survival which may have implications in the treatment of diabetes. What advances does it highlight? This review highlights how exercise may modulate β-cell health in the context of diabetes and highlights the need for further exploration of whether β-cell preserving effects of exercise translates to T1D.

ABSTRACT

Physical exercise is a core therapy for type 1 and type 2 diabetes. Whilst the benefits of exercise for different physiological systems are recognised, the effect of exercise specifically on the pancreatic β-cell is not well described. Here we review the effects of physical exercise on β-cell health. We show that exercise improves β-cell mass and function. The improved function manifests primarily through the increased insulin content of the β-cell and its increased ability to secrete insulin in response to a glucose stimulus. We review the evidence relating to glucose sensing, insulin signalling, β-cell proliferation and β-cell apoptosis in humans and animal models with acute exercise and following exercise training programmes. Some of the mechanisms through which these benefits manifest are discussed.

Exercise improves metabolic function and alters the microbiome in rats with gestational diabetes

Gestational diabetes mellitus (GDM) is a common pregnancy complication, particularly prevalent in obese women. Importantly, exercise has beneficial impacts on maternal glucose control and may prevent GDM in "at-risk" women. We aimed to determine whether a high-fat diet (HFD) exacerbates metabolic dysfunction and alters gut microbiome in GDM and whether endurance exercise prevents these changes. Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (Restricted) or sham (Control) surgery on E18 in Wistar-Kyoto rats. Female offspring were fed a Chow or HFD (23% fat) from weaning (5 weeks) and at 16 weeks randomly allocated to remain Sedentary or to an exercise protocol of either Exercise prior to and during pregnancy (Exercise); or Exercise during pregnancy only (PregEx). Females were mated (20 weeks) and underwent indirect calorimetry (embryonic day 16; E16), glucose tolerance testing (E18), followed by 24-hr feces collection at E19 (n = 8-10/group). HFD consumption in female rats with GDM exacerbated the adverse metabolic adaptations to pregnancy and altered gut microbial populations. Specifically, the Firmicutes-to-Bacteroidetes ratio was increased, due to an underlying change in abundance of the orders Clostridiales and Bacteroidales. Maternal Exercise, but not PregEx, prevented the development of metabolic dysfunction, increased pancreatic β-cell mass, and prevented the alteration of the gut microbiome in GDM females. Our findings suggest that maternal exercise and diet influence metabolic and microbiome dysfunction in females with GDM, which may impact long-term maternal and offspring health.

Exercise initiated during pregnancy in rats born growth restricted alters placental mTOR and nutrient transporter expression

KEY POINTS

Fetal growth is dependent on effective placental nutrient transportation, which is regulated by mammalian target of rapamycin (mTOR) complex 1 modulation of nutrient transporter expression. These transporters are dysregulated in pregnancies affected by uteroplacental insufficiency and maternal obesity. Nutrient transporters and mTOR were altered in placentae of mothers born growth restricted compared to normal birth weight dams, with maternal diet- and fetal sex-specific responses. Exercise initiated during pregnancy downregulated mTOR protein expression, despite an increase in mTOR activation in male associated placentae, and reduced nutrient transporter gene abundance, which was also dependent on maternal diet and fetal sex. Limited changes were characterized with exercise initiated before and continued throughout pregnancy in nutrient transporter and mTOR expression. Maternal exercise during pregnancy differentially regulated mTOR and nutrient transporters in a diet- and sex-specific manner, which likely aimed to improve late gestational placental growth and neonatal survival.

ABSTRACT

Adequate transplacental nutrient delivery is essential for fetoplacental development. Intrauterine growth restriction and maternal obesity independently alter placental nutrient transporter expression. Although exercise is beneficial for maternal health, limited studies have characterized how the timing of exercise initiation influences placental nutrient transport. Therefore, this study investigated the impact of maternal exercise on placental mechanistic target of rapamycin (mTOR) and nutrient transporter expression in growth restricted mothers and whether these outcomes were dependent on maternal diet or fetal sex. Uteroplacental insufficiency or sham surgery was induced on embryonic day (E) 18 in Wistar-Kyoto rats. F1 offspring were fed a chow or high-fat diet from weaning and at 16 weeks were randomly allocated to an exercise protocol: sedentary, exercised prior to and during pregnancy, or exercised during pregnancy only. Females were mated with normal males (20 weeks) and F2 placentae collected at E20. Exercise during pregnancy only, reduced mTOR protein expression in all groups and increased mTOR activation in male associated placentae. Exercise during pregnancy only, decreased the expression of amino acid transporters in a diet- and sex-specific manner. Maternal growth restriction altered mTOR and system A amino acid transporter expression in a sex- and diet-specific manner. These data highlight that maternal exercise initiated during pregnancy alters placental mTOR expression, which may directly regulate amino acid transporter expression, to a greater extent than exercise initiated prior to and continued during pregnancy, in a diet- and fetal sex-dependent manner. These findings highlight that the timing of exercise initiation is important for optimal placental function.

Maternal exercise and growth restriction in rats alters placental angiogenic factors and blood space area in a sex-specific manner

Fetal growth and development are dependent on adequate placental nutrient transfer. The surface area of the placental villous network is a key determinant of nutrient exchange, which is regulated by vasculogenic and angiogenic factors. These factors are altered by intrauterine growth restriction (IUGR) and maternal obesity in both the first (F1) and second (F2) generations. We investigated the impact of endurance exercise in IUGR dams fed a High-fat diet on placental vasculogenesis and angiogenesis. Uteroplacental insufficiency (Restricted) or sham (Control) surgery was induced on embryonic day (E) 18 in Wistar-Kyoto rats. F1 offspring were fed a Chow or High-fat diet from weaning, and at 16 weeks were further allocated an exercise protocol; Sedentary, Exercised prior to and during pregnancy (Exercise), or Exercised during pregnancy only (PregEx). Females were mated (20 weeks) and F2 placentae collected at E20. Maternal Restriction, High-fat feeding and Exercise had a minimal impact on placental regulators of vasculogenesis and angiogenesis. However, Restriction increased placental labyrinth tissue area in Chow-fed dams. PregEx induced overt adaptations, including increased VEGFA and decreased PLGF protein expression, and reduced blood space area. These alterations were sex-dependent and associated with alterations in miRNA27a, a known regulator of VEGF translation. These data highlight that maternal exercise initiated during pregnancy (PregEx) causes alterations in placental vasculogenesis and angiogenesis in a sex-dependent manner, with minimal Restriction and maternal diet effects. However, further investigation is required to determine if these adaptations are beneficial or harmful for maternal and fetoplacental outcomes.

Four weeks of exercise early in life reprograms adult skeletal muscle insulin resistance caused by a paternal high-fat diet

KEY POINTS

A paternal high-fat diet/obesity before mating can negatively influence the metabolism of offspring. Exercise only early in life has a remarkable effect with respect to reprogramming adult rat offspring exposed to detrimental insults before conception. Exercise only early in life normalized adult whole body and muscle insulin resistance as a result of having a high-fat fed/obese father. Unlike the effects on the muscle, early exercise did not normalize the reduced adult pancreatic beta cell mass as a result of having a high-fat fed/obese father. Early-life exercise training may be able to reprogram an individual whose father was obese, inducing long-lasting beneficial effects on health.

ABSTRACT

A paternal high-fat diet (HFD) impairs female rat offspring glucose tolerance, pancreatic morphology and insulin secretion. We examined whether only 4 weeks of exercise early in life could reprogram these negative effects. Male Sprague-Dawley rats consumed a HFD for 10 weeks before mating with chow-fed dams. Female offspring remained sedentary or performed moderate intensity treadmill exercise (5 days week^-1 , 60 min day^-1 , 20 m min^-1 ) from 5 to 9 weeks of age. Paternal HFD impaired (P < 0.05) adult offspring whole body insulin sensitivity (i.p. insulin sensitivity test), as well as skeletal muscle ex vivo insulin sensitivity and TBC1D4 phosphorylation. It also lowered β-cell mass and reduced in vivo insulin secretion in response to an i.p. glucose tolerance test. Early-life exercise in offspring reprogrammed the negative effects of a paternal HFD on whole body insulin sensitivity, skeletal muscle ex vivo insulin-stimulated glucose uptake and TBC1D4 phosphorylation and also increased glucose transporter 4 protein. However, early exercise did not normalize the reduced pancreatic β-cell mass or insulin secretion. In conclusion, only 4 weeks of exercise early in life in female rat offspring reprograms reductions in insulin sensitivity in adulthood caused by a paternal HFD without affecting pancreatic β-cell mass or insulin secretion.

Is willingness to exercise programmed in utero? Reviewing sedentary behavior and the benefits of physical activity in intrauterine growth restricted individuals

OBJECTIVE

The literature suggests that a fetus will adapt to surrounding adversities by optimizing its use of energy to improve survival, ultimately leading to the programming of the individual's energy intake and expenditure. While recent reviews focused on the fetal programming of energy intake and food preferences, there is also some evidence that fetal adversity is associated with diminished physical activity levels. Therefore, we aimed to review (a) the evidence for an association between being born with intrauterine growth restriction and sedentarism over the life-course and (b) the potential benefits of physical activity over cardiometabolic risk factors for this population.

SOURCES

PubMed, Scielo, Scopus and Embase.

SUMMARY OF FINDINGS

Most clinical studies that used objective measures found no association between intrauterine growth restriction and physical activity levels, while most studies that used self-reported questionnaires revealed such relationships, particularly leisure time physical activity. Experimental studies support the existence of fetal programming of physical activity, and show that exposure to exercise during IUGR individuals' life improves metabolic outcomes but less effect was seen on muscle architecture or function.

CONCLUSIONS

Alterations in muscle strength and metabolism, as well as altered aerobic performance, may predispose IUGR individuals to be spontaneously less physically active, suggesting that this population may be an important target for preventive interventions. Although very heterogeneous, the different studies allow us to infer that physical activity may have beneficial effects especially for individuals that are more vulnerable to metabolic modifications such as those with IUGR.

Fetal growth restriction shortens cardiac telomere length, but this is attenuated by exercise in early life

BACKGROUND AND AIMS

Fetal and postnatal growth restriction cause a predisposition to cardiovascular disease (CVD) in adulthood. Telomeres are repetitive DNA-protein structures that protect chromosome ends, and the loss of these repeats (a reduction in telomere length) is associated with CVD. As exercise preserves telomere length and cardiovascular health, the aim of this study was to determine the effects of growth restriction and exercise training on cardiac telomere length and telomeric genes.

METHODS AND RESULTS

Pregnant Wistar Kyoto rats underwent bilateral uterine vessel ligation to induce uteroplacental insufficiency and fetal growth restriction ("Restricted"). Sham-operated rats had either intact litters ("Control") or their litters reduced to five pups with slowed postnatal growth ("Reduced"). Control, Restricted, and Reduced male rats were assigned to Sedentary, Early exercise (5-9 wk of age), or Late exercise (20-24 wk of age) groups. Hearts were excised at 24 wk of age for telomere length and gene expression measurements by quantitative PCR. Growth restriction shortened cardiac telomere length ( P < 0.001), but this was rescued by early exercise ( P < 0.001). Early and Late exercise increased cardiac weight index ( P < 0.001), but neither this nor telomere length was associated with expression of the telomeric genes Tert, Terc, Trf2, Pnuts, or Sirt1.

DISCUSSION AND CONCLUSIONS

Growth restriction shortens cardiac telomere length, reflecting the cardiac pathologies associated with low birth weight. Exercise in early life may offer long-term protective effects on cardiac telomere length, which could help prevent CVD in later life.

Maternal exercise in rats upregulates the placental insulin-like growth factor system with diet- and sex-specific responses: minimal effects in mothers born growth restricted

KEY POINTS

The placental insulin-like growth factor (IGF) system is critical for normal fetoplacental growth, which is dysregulated following several pregnancy perturbations including uteroplacental insufficiency and maternal obesity. We report that the IGF system was altered in placentae of mothers born growth restricted compared to normal birth weight mothers, with maternal diet- and fetal sex-specific responses. Additionally, we report increased body weight and plasma IGF1 concentrations in fetuses from chow-fed normal birth weight mothers that exercised prior to and continued during pregnancy compared to sedentary mothers. Exercise initiated during pregnancy, on the other hand, resulted in placental morphological alterations and increased IGF1 and IGF1R protein expression, which may in part be modulated by reduced Let 7f-1 miRNA abundance. Growth restriction of mothers before birth and exercise differentially regulate the placental IGF system with diet- and sex-specific responses, probably as a means to improve fetoplacental growth and development, and hence neonatal survival. This increased neonatal survival may prevent adult disease onset.

ABSTRACT

The insulin-like growth factor (IGF) system regulates fetoplacental growth and plays a role in disease programming. Dysregulation of the IGF system is implicated in several pregnancy perturbations associated with altered fetal growth, including intrauterine growth restriction and maternal obesity. Limited human studies have demonstrated that maternal exercise enhances fetoplacental growth and decreases cord IGF ligands, which may restore the placental IGF system in complicated pregnancies. This study investigated the impact maternal exercise has on the placental IGF system in placentae from mothers born growth restricted and if these outcomes are dependent on maternal diet or fetal sex. Uteroplacental insufficiency (Restricted) or sham (Control) surgery was induced on embryonic day (E) 18 in Wistar-Kyoto rats. F1 offspring were fed a chow or high-fat diet from weaning, and at 16 weeks were randomly allocated an exercise protocol: Sedentary, Exercised prior to and during pregnancy (Exercise), or Exercised during pregnancy only (PregEx). Females were mated (20 weeks) with placentae associated with F2 fetuses collected at E20. The placental IGF system mRNA abundance and placental morphology was altered in mothers born growth restricted. Exercise increased fetal weight and Control plasma IGF1 concentrations, and decreased female placental weight. PregEx did not influence fetoplacental growth but increased placental IGF1 and IGF1R (potentially modulated by reduced Let 7f-1 miRNA) and decreased placental IGF2 protein. Importantly, these placental IGF system changes occurred with sex-specific responses. These data highlight that exercise differently influences fetoplacental growth and the placental IGF system depending on maternal exercise initiation, which may prevent the transgenerational transmission of deficits and dysfunction.

Angiotensin receptor blockade in juvenile male rat offspring: Implications for long-term cardio-renal health

Inhibition of the renin-angiotensin system in early postnatal life is a potential therapeutic approach to prevent long-term cardiovascular and kidney diseases in individuals born small. We determined the long-term effects of juvenile losartan treatment on cardiovascular and kidney function in control male rat offspring and those exposed to uteroplacental insufficiency and born small. Bilateral uterine vessel ligation (Restricted) or sham (Control) surgery was performed in late gestation in Wistar Kyoto rats. At weaning, male offspring were randomly assigned to receive losartan in their drinking water or drinking water alone from 5 to 8 weeks of age, and followed to 26 weeks of age. Systolic blood pressure and kidney function were assessed throughout the study. Pressure myography was used to assess passive mechanical wall properties in mesenteric and femoral arteries from 26-week-old offspring. Losartan treatment for three weeks lowered systolic blood pressure in both Control and Restricted groups but this difference was not sustained after the cessation of treatment. Losartan, irrespective of birth weight, mildly increased renal tubulointerstitial fibrosis when assessed at 26 weeks of age. Mesenteric artery stiffness was increased by the early losartan treatment, and was associated with increased collagen and decreased elastin content. Losartan also exerted long-term increases in fat mass and decreases in skeletal muscle mass. In this study, untreated Restricted offspring did not develop hypertension, vascular dysfunction or kidney changes as anticipated. Regardless, we demonstrate that short-term losartan treatment in the juvenile period negatively affects postnatal growth, and kidney and vascular parameters in adulthood, irrespective of birth weight. The long-term effects of early-life losartan treatment warrant further consideration in settings where the potential benefits may outweigh the risks; i.e. when programmed adulthood diseases are apparent and in childhood cardiovascular and kidney diseases.

Sustained cardiac programming by short-term juvenile exercise training in male rats

KEY POINTS

Cardiac hypertrophy following endurance-training is thought to be due to hypertrophy of existing cardiomyocytes. The benefits of endurance exercise on cardiac hypertrophy are generally thought to be short-lived and regress to sedentary levels within a few weeks of stopping endurance training. We have now established that cardiomyocyte hyperplasia also plays a considerable role in cardiac growth in response to just 4 weeks of endurance exercise in juvenile (5-9 weeks of age) rats. The effect of endurance exercise on cardiomyocyte hyperplasia diminishes with age and is lost by adulthood. We have also established that the effect of juvenile exercise on heart mass is sustained into adulthood.

ABSTRACT

The aim of this study was to investigate if endurance training during juvenile life 'reprogrammes' the heart and leads to sustained improvements in the structure, function, and morphology of the adult heart. Male Wistar Kyoto rats were exercise trained 5 days week^-1 for 4 weeks in either juvenile (5-9 weeks of age), adolescent (11-15 weeks of age) or adult life (20-24 weeks of age). Juvenile exercise training, when compared to 24-week-old sedentary rats, led to sustained increases in left ventricle (LV) mass (+18%; P < 0.05), wall thickness (+11%; P < 0.05), the longitudinal area of binucleated cardiomyocytes (P < 0.05), cardiomyocyte number (+36%; P < 0.05), and doubled the proportion of mononucleated cardiomyocytes (P < 0.05), with a less pronounced effect of exercise during adolescent life. Adult exercise training also increased LV mass (+11%; P < 0.05), wall thickness (+6%; P < 0.05) and the longitudinal area of binucleated cardiomyocytes (P < 0.05), despite no change in cardiomyocyte number or the proportion of mono- and binucleated cardiomyocytes. Resting cardiac function, LV chamber dimensions and fibrosis levels were not altered by juvenile or adult exercise training. At 9 weeks of age, juvenile exercise significantly reduced the expression of microRNA-208b, which is a known regulator of cardiac growth, but this was not sustained to 24 weeks of age. In conclusion, juvenile exercise leads to physiological cardiac hypertrophy that is sustained into adulthood long after exercise training has ceased. Furthermore, this cardiac reprogramming is largely due to a 36% increase in cardiomyocyte number, which results in an additional 20 million cardiomyocytes in adulthood.

Intrauterine Growth Restriction: Hungry for an Answer

Intrauterine growth restriction (IUGR) has been defined in several ways, but in general describes a condition in which the fetus exhibits poor growth in utero. This complication of pregnancy poses a significant public health burden as well as increased morbidity and mortality for the offspring. In human IUGR, alteration in fetal glucose and insulin homeostasis occurs in an effort to conserve energy and survive at the expense of fetal growth in an environment of inadequate nutrient provision. Several animal models of IUGR have been utilized to study the effects of IUGR on fetal glucose handling, as well as the postnatal reprogramming of energy metabolite handling, which may be unmasked in adulthood as a maladaptive propensity for cardiometabolic disease. This developmental programming may be mediated in part by epigenetic modification of essential regulators of glucose homeostasis. Several pharmacological therapies and nonpharmacological lifestyle modifications have shown early promise in mitigating the risk for or severity of adult metabolic phenotypes but still require further study of unanticipated and/or untoward side effects.

Does exercise pose a challenge to glucoregulation after clinical islet transplantation?

Islet transplantation (ITx) is effective in preventing severe hypoglycemia by restoring glucose-dependent insulin secretion in type 1 diabetes (T1D), but may not normalize glucose regulation. Studies suggest that physical activity plays a role in maintaining β-cell mass and function in individuals with type 2 diabetes and animal models of diabetes. This could indicate that physical activity plays a role in graft survival in ITx recipients. This review's objective is to assess current knowledge related to physical activity in ITx recipients. Responses to other challenges in blood glucose control (i.e., hypoglycemia) in human ITx recipients were examined to provide in-depth background information. To identify studies involving exercise in ITx recipients, a systematic search was performed using PubMed, Medline, and Embase, which revealed 277 English language publications. Publications were excluded if they did not involve ITx recipients; did not involve physical activity or hypoglycemia; or did not report on glucose, insulin, or counterregulatory hormones. During induced hypoglycemia, studies indicate normal suppression of insulin in ITx individuals compared with healthy non-T1D controls. Studies involving exercise in ITx animals have conflicting results, with time since transplantation and transplantation site (spleen, liver, kidney, peritoneal cavity) as possible confounders. No study examining blood glucose responses to physical activity in human ITx recipients was identified. A small number of induced-hypoglycemia studies in humans, and exercise studies in animals, would suggest that glucoregulation is greatly improved yet is still imperfect in this population and that ITx does not fully restore counterregulatory responses to challenges in blood glucose homeostasis.

Sex-Specific Metabolic Outcomes in Offspring of Female Rats Born Small or Exposed to Stress During Pregnancy

Low birth weight increases adult metabolic disease risk in both the first (F1) and second (F2) generation. Physiological stress during pregnancy in F1 females that were born small induces F2 fetal growth restriction, but the long-term metabolic health of these F2 offspring is unknown. Uteroplacental insufficiency (restricted) or sham (control) surgery was performed in F0 rats. F1 females (control, restricted) were allocated to unstressed or stressed pregnancies. F2 offspring exposed to maternal stress in utero had reduced birth weight. At 6 months, F2 stressed males had elevated fasting glucose. In contrast, F2 restricted males had reduced pancreatic β-cell mass. Interestingly, these metabolic deficits were not present at 12 month. F2 males had increased adrenal mRNA expression of steroidogenic acute regulatory protein and IGF-1 receptor when their mothers were born small or exposed to stress during pregnancy. Stressed control F2 males had increased expression of adrenal genes that regulate androgen signaling at 6 months, whereas expression increased in restricted male and female offspring at 12 months. F2 females from stressed mothers had lower area under the glucose curve during glucose tolerance testing at 12 months compared with unstressed females but were otherwise unaffected. If F1 mothers were either born small or exposed to stress during her pregnancy, F2 offspring had impaired physiological outcomes in a sex- and age-specific manner. Importantly, stress during pregnancy did not exacerbate disease risk in F2 offspring of mothers born small, suggesting that they independently program disease in offspring through different mechanisms.

Adrenal, metabolic and cardio-renal dysfunction develops after pregnancy in rats born small or stressed by physiological measurements during pregnancy

KEY POINTS

Women born small are at an increased risk of developing pregnancy complications. Stress may further increase a woman's likelihood for an adverse pregnancy. Adverse pregnancy adaptations can lead to long-term diseases even after her pregnancy. The current study investigated the effects of stress during pregnancy on the long-term adrenal, metabolic and cardio-renal health of female rats that were born small. Stress programmed increased adrenal Mc2r gene expression, a higher insulin secretory response to glucose during intraperitoneal glucose tolerance test (+36%) and elevated renal creatinine clearance after pregnancy. Females that were born small had increased homeostatic model assessment-insulin resistance and elevated systolic blood pressure after pregnancy, regardless of stress exposure. These findings suggest that being born small or being stressed during pregnancy programs long-term adverse health outcomes after pregnancy. However, stress in pregnancy does not exacerbate the long-term adverse health outcomes for females that were born small.

ABSTRACT

Females born small are more likely to experience complications during their pregnancy, including pregnancy-induced hypertension, pre-eclampsia and gestational diabetes. The risk of developing complications is increased by stress exposure during pregnancy. In addition, pregnancy complications may predispose the mother to diseases after pregnancy. We determined whether stress during pregnancy would exacerbate the adrenal, metabolic and cardio-renal dysfunction of growth-restricted females in later life. Late gestation bilateral uterine vessel ligation was performed in Wistar Kyoto rats to induce growth restriction. At 4 months, growth-restricted and control female offspring were mated with normal males. Those allocated to the stressed group had physiological measurements [metabolic cage, tail cuff blood pressure, intraperitoneal glucose tolerance test (IPGTT)] conducted during pregnancy whilst the unstressed groups were unhandled. After the completion of pregnancy, dams were aged to 12 months and blood pressure, and metabolic and renal function were assessed. At 13 months, adrenal glands, pancreases and plasma were collected at post-mortem. Females stressed during pregnancy had increased adrenal Mc2r gene expression (+22%), higher insulin secretory response to glucose during IPGTT (+36%) and higher creatinine clearance (+29%, indicating increased estimated glomerular filtration rate). In contrast, females that were born small had increased homeostatic model assessment-insulin resistance (+54%), increased water intake (+23%), urine output (+44%) and elevated systolic blood pressure (+7%) regardless of exposure to stress. Our findings suggest that low maternal birth weight and maternal stress exposure during pregnancy are both independently detrimental for long-term adrenal, metabolic and cardio-renal health of the mother, although their effects were not exacerbated.

Endurance training in early life results in long-term programming of heart mass in rats

Being born small for gestational age increases the risk of developing adult cardiovascular and metabolic diseases. This study aimed to examine if early‐life exercise could increase heart mass in the adult hearts from growth restricted rats. Bilateral uterine vessel ligation to induce uteroplacental insufficiency and fetal growth restriction in the offspring (Restricted) or sham surgery (Control) was performed on day 18 of gestation in WKY rats. A separate group of sham litters had litter size reduced to five pups at birth (Reduced litter), which restricted postnatal growth. Male offspring remained sedentary or underwent treadmill running from 5 to 9 weeks (early exercise) or 20 to 24 weeks of age (later exercise). Remarkably, in Control, Restricted, and Reduced litter groups, early exercise increased (P < 0.05) absolute and relative (to body mass) heart mass in adulthood. This was despite the animals being sedentary for ~4 months after exercise. Later exercise also increased adult absolute and relative heart mass (P < 0.05). Blood pressure was not significantly altered between groups or by early or later exercise. Phosphorylation of Akt Ser⁴⁷³ in adulthood was increased in the early exercise groups but not the later exercise groups. Microarray gene analysis and validation by real‐time PCR did not reveal any long‐term effects of early exercise on the expression of any individual genes. In summary, early exercise programs the heart for increased mass into adulthood, perhaps by an upregulation of protein synthesis based on greater phosphorylation of Akt Ser⁴⁷³.

Programming of maternal and offspring disease: impact of growth restriction, fetal sex and transmission across generations

Babies born small are at an increased risk of developing myriad adult diseases. While growth restriction increases disease risk in all individuals, often a second hit is required to unmask 'programmed' impairments in physiology. Programmed disease outcomes are demonstrated more commonly in male offspring compared with females, with these sex-specific outcomes partly attributed to different placenta-regulated growth strategies of the male and female fetus. Pregnancy is known to be a major risk factor for unmasking a number of conditions and can be considered a 'second hit' for women who were born small. As such, female offspring often develop impairments of physiology for the first time during pregnancy that present as pregnancy complications. Numerous maternal stressors can further increase the risk of developing a maternal complication during pregnancy. Importantly, these maternal complications can have long-term consequences for both the mother after pregnancy and the developing fetus. Conditions such as preeclampsia, gestational diabetes and hypertension as well as thyroid, liver and kidney diseases are all conditions that can complicate pregnancy and have long-term consequences for maternal and offspring health. Babies born to mothers who develop these conditions are often at a greater risk of developing disease in adulthood. This has implications as a mechanism for transmission of disease across generations. In this review, we discuss the evidence surrounding long-term intergenerational implications of being born small and/or experiencing stress during pregnancy on programming outcomes.

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.

Uteroplacental insufficiency leads to hypertension, but not glucose intolerance or impaired skeletal muscle mitochondrial biogenesis, in 12-month-old rats

Growth restriction impacts on offspring development and increases their risk of disease in adulthood which is exacerbated with “second hits.” The aim of this study was to investigate if blood pressure, glucose tolerance, and skeletal muscle mitochondrial biogenesis were altered in 12-month-old male and female offspring with prenatal or postnatal growth restriction. Bilateral uterine vessel ligation induced uteroplacental insufficiency and growth restriction in offspring (Restricted). A sham surgery was also performed during pregnancy (Control) and some litters from sham mothers had their litter size reduced (Reduced litter), which restricted postnatal growth. Growth-restricted females only developed hypertension at 12 months, which was not observed in males. In Restricted females only homeostasis model assessment for insulin resistance was decreased, indicating enhanced hepatic insulin sensitivity, which was not observed in males. Plasma leptin was increased only in the Reduced males at 12 months compared to Control and Restricted males, which was not observed in females. Compared to Controls, leptin, ghrelin, and adiponectin were unaltered in the Restricted males and females, suggesting that at 12 months of age the reduction in body weight in the Restricted offspring is not a consequence of circulating adipokines. Skeletal muscle PGC-1α levels were unaltered in 12-month-old male and female rats, which indicate improvements in lean muscle mass by 12 months of age. In summary, sex strongly impacts the cardiometabolic effects of growth restriction in 12-month-old rats and it is females who are at particular risk of developing long-term hypertension following growth restriction.

Aerobic exercise training reduces cardiac function in adult male offspring exposed to prenatal hypoxia

Intrauterine growth restriction (IUGR) has been associated with increased susceptibility to myocardial ischemia-reperfusion (I/R) injury. Exercise is an effective preventive intervention for cardiovascular diseases; however, it may be detrimental in conditions of compromised health. The aim of this study was to determine whether exercise training can improve cardiac performance after I/R injury in IUGR offspring. We used a hypoxia-induced IUGR model by exposing pregnant Sprague-Dawley rats to 21% oxygen (control) or hypoxic (11% oxygen; IUGR) conditions from gestational day 15 to 21. At 10 wk of age, offspring were randomized to a sedentary group or to a 6-wk exercise protocol. Transthoracic echocardiography assessments were performed after 6 wk. Twenty-four hours after the last bout of exercise, ex vivo cardiac function was determined using a working heart preparation. With exercise training, there was improved baseline cardiac performance in male control offspring but a reduced baseline cardiac performance in male IUGR exercised offspring ( P < 0.05). In male offspring, exercise decreased superoxide generation in control offspring, while in IUGR offspring, it had the polar opposite effect (interaction P ≤ 0.05). There was no effect of IUGR or exercise on cardiac function in female offspring. In conclusion, in male IUGR offspring, exercise may be a secondary stressor on cardiac function. A reduction in cardiac performance along with an increase in superoxide production in response to exercise was observed in this susceptible group.

Fathers that are born small program alterations in the next-generation preimplantation rat embryos

BACKGROUND

Low birth weight is associated with increased risk of adult cardiovascular and metabolic disease development, with recent studies highlighting transmission to subsequent generations via both maternal and paternal lines. However, the timing of parent-specific programming of disease risk to the next generation remains to be characterized.

OBJECTIVE

The aim of this study was to examine how paternal low birth weight affects the cellular and molecular physiology of the next-generation [second-generation (F2)] blastocysts, before uterine implantation.

METHODS

Uteroplacental insufficiency was surgically induced in Wistar Kyoto pregnant rats in late gestation, giving rise to first-generation restricted (born small) and sham-operated control (normal birth weight) male offspring, respectively. First-generation restricted and control male rats were naturally mated with normal females.

RESULTS

Resultant F2 blastocysts derived from restricted males displayed reduced expression of growth regulatory genes of the mammalian target of rapamycin pathway compared with F2 control blastocysts (9-74%; P < 0.05). No differences were found in F2 restricted blastocyst structural characteristics, cell number, or carbohydrate utilization at the time of blastocyst retrieval or after 24 h of in vitro culture. However, histidine, methionine, pyruvate, serine, and tryosine consumption and aspartate and leucine production were greater in F2 restricted outgrowth than in controls (P < 0.05).

CONCLUSIONS

The findings from this study clearly indicate that male rat offspring born small, arising from uteroplacental insufficiency, have physiologic alterations that manifest as modifications in gene expression levels and nutrient metabolism of F2 blastocysts, even in the absence of overt cellular growth differences. These data demonstrate that growth restriction and associated disease risk have the capacity to be transmitted to the next generation of offspring via the male germ line and is manifest as early as the blastocyst stage of development.

Vascular effects of aerobic exercise training in rat adult offspring exposed to hypoxia-induced intrauterine growth restriction

KEY POINTS

Prenatal hypoxia, one of the most common consequences of complicated pregnancies, leads to intrauterine growth restriction (IUGR) and impairs later-life endothelium-dependent vascular function. Early interventions are needed to ultimately reduce later-life risk for cardiovascular disease. Aerobic exercise training has been shown to prevent cardiovascular diseases. Whether exercise can be used as an intervention to reverse the vascular phenotype of this susceptible population is unknown. Aerobic exercise training enhanced endothelium-derived hyperpolarization-mediated vasodilatation in gastrocnemius muscle arteries in male IUGR offspring, and did not improve nitric oxide-mediated vasodilatation in IUGR offspring. Understanding the mechanisms by which exercise impacts the cardiovascular system in a susceptible population and the consideration of sexual dimorphism is essential to define whether exercise could be used as a preventive strategy in this population.

ABSTRACT

Hypoxia in utero is a critical insult causing intrauterine growth restriction (IUGR). Adult offspring born with hypoxia-induced IUGR have impaired endothelium-dependent vascular function. We tested whether aerobic exercise improves IUGR-induced endothelial dysfunction. Pregnant Sprague-Dawley rats were exposed to control (21% oxygen) or hypoxic (11% oxygen) conditions from gestational day 15 to 21. Male and female offspring from normoxic and hypoxic (IUGR) pregnancies were randomized at 10 weeks of age to either an exercise-trained or sedentary group. Exercise-trained rats ran on a treadmill for 30 min at 20 m min(-1) , 5 deg gradient, 5 days week(-1) , for 6 weeks. Concentration-response curves to phenylephrine and methylcholine were performed in second order mesenteric and gastrocnemius muscle arteries, in the presence or absence of l-NAME (100 μm), MnTBAP (peroxynitrite scavenger; 10 μm), apamin (0.1 μm) and TRAM-34 (an intermediate-conductance calcium-activated potassium channel blocker; 10 μm), or indomethacin (5 μm). In adult male IUGR offspring, prenatal hypoxia had no effect on total vasodilator responses in either vascular bed. Aerobic exercise training in IUGR males, however, improved endothelium-derived hyperpolarization (EDH)-mediated vasodilatation in gastrocnemius muscle arteries. Female IUGR offspring had reduced NO-mediated vasodilatation in both vascular beds, along with decreased total vasodilator responses and increased prostaglandin-mediated vasoconstriction in gastrocnemius muscle arteries. In contrast to males, aerobic exercise training in IUGR female offspring had no effect on either vascular bed. Exercise may not prove to be a beneficial therapy for specific vascular pathways affected by prenatal hypoxia, particularly in female offspring.

The time has come to test the beta cell preserving effects of exercise in patients with new onset type 1 diabetes

Type 1 diabetes is characterised by immune-mediated destruction of insulin-producing beta cells. Significant beta cell function is usually present at the time of diagnosis with type 1 diabetes, and preservation of this function has important clinical benefits. The last 30 years have seen a number of largely unsuccessful trials for beta cell preservation, some of which have been of therapies that have potential for significant harm. There is a need to explore new, more tolerable approaches to preserving beta cell function that can be implemented on a large clinical scale. Here we review the evidence for physical exercise as a therapy for the preservation of beta cell function in patients with newly diagnosed type 1 diabetes. We highlight possible mechanisms by which exercise could preserve beta cell function and then present evidence from other models of diabetes that demonstrate that exercise preserves beta cell function. We conclude by proposing that there is now a need for studies to explore whether exercise can preserve beta cell in patients newly diagnosed with type 1 diabetes.

Developmental programming: variations in early growth and adult disease

Suboptimal conditions in utero are associated with the development of adult-onset diseases in offspring. Uteroplacental insufficiency in rats is a well-established animal model used to mimic and study the effects of developmental insults relevant to countries of abundant nutrient supply. However, wide-ranging outcomes for the offspring are apparent between the different investigators that use this model and also between cohorts generated in our laboratory. We aimed to explore the reasons for variability in rat models of uteroplacental insufficiency between different investigators and also between our own animal cohorts. We suggest differences in growth and disease development reflect uniqueness in susceptibility and highlight the complexity of interactions between genetic potential and environmental exposures. The impact of adverse exposures in utero has been described as having far-reaching effects that extend well beyond the first, directly exposed generation. However, the resulting phenotypes are not consistent between generations. This suggests that programmed effects are established de novo in each generation and challenges the prediction of disease. Characterization of growth and disease in the numerous rat models has led to our understanding of the impact of early life experiences on adult health. In order to drive the development of preventative and/or treatment strategies, future studies should focus on identifying the initial cause(s) of uteroplacental insufficiency, including genetic origins and the influence of poor diets.

Exercise as an intervention to improve metabolic outcomes after intrauterine growth restriction

Individuals born after intrauterine growth restriction (IUGR) are at an increased risk of developing diabetes in their adult life. IUGR impairs β-cell function and reduces β-cell mass, thereby diminishing insulin secretion. IUGR also induces insulin resistance, with impaired insulin signaling in muscle in adult humans who were small for gestational age (SGA) and in rodent models of IUGR. There is epidemiological evidence in humans that exercise in adults can reduce the risk of metabolic disease following IUGR. However, it is not clear whether adult IUGR individuals benefit to the same extent from exercise as do normal-birth-weight individuals, as our rat studies suggest less of a benefit in those born IUGR. Importantly, however, there is some evidence from studies in rats that exercise in early life might be able to reverse or reprogram the long-term metabolic effects of IUGR. Studies are needed to address gaps in current knowledge, including determining the mechanisms involved in the reprogramming effects of early exercise in rats, whether exercise early in life or in adulthood has similar beneficial metabolic effects in larger animal models in which insulin resistance develops after IUGR. Human studies are also needed to determine whether exercise training improves insulin secretion and insulin sensitivity to the same extent in IUGR adults as in control populations. Such investigations will have implications for customizing the recommended level and timing of exercise to improve metabolic health after IUGR.

Islet inflammation, hemosiderosis, and fibrosis in intrauterine growth-restricted and high fat-fed Sprague-Dawley rats

Prenatal and postnatal factors such as intrauterine growth restriction (IUGR) and high-fat (HF) diet contribute to type 2 diabetes. Our aim was to determine whether IUGR and HF diets interact in type 2 diabetes pathogenesis, with particular attention focused on pancreatic islet morphology including assessment for inflammation. A surgical model of IUGR (bilateral uterine artery ligation) in Sprague-Dawley rats with sham controls was used. Pups were fed either HF or chow diets after weaning. Serial measures of body weight and glucose tolerance were performed. At 25 weeks of age, rat pancreases were harvested for histologic assessment. The birth weight of IUGR pups was 13% lower than that of sham pups. HF diet caused excess weight gain, dyslipidemia, hyperinsulinemia, and mild glucose intolerance, however, this was not aggravated further by IUGR. Markedly abnormal islet morphology was evident in 0 of 6 sham-chow, 5 of 8 sham-HF, 4 of 8 IUGR-chow, and 8 of 9 IUGR-HF rats (chi-square, P = 0.007). Abnormal islets were characterized by larger size, irregular shape, inflammation with CD68-positive cells, marked fibrosis, and hemosiderosis. β-Cell mass was not altered by IUGR. In conclusion, HF and IUGR independently contribute to islet injury characterized by inflammation, hemosiderosis, and fibrosis. This suggests that both HF and IUGR can induce islet injury via converging pathways. The potential pathogenic or permissive role of iron in this process of islet inflammation warrants further investigation.

Embryo transfer cannot delineate between the maternal pregnancy environment and germ line effects in the transgenerational transmission of disease in rats

Adverse conditions in utero can have transgenerational effects, in the absence of a subsequent insult. We aimed to investigate the contribution of the maternal pregnancy environment vs. germ line effects in mediating alterations to cardiorenal and metabolic physiology in offspring from mothers born small. Uteroplacental insufficiency was induced by bilateral uterine artery and vein ligation (Restricted group) or sham surgery (Control group) in Wistar-Kyoto rats. Restricted and control female offspring (F1) were mated with either breeder males (embryo donor) or vasectomized males (embryo recipient). Embryo transfer was performed at embryonic day (E) 1, whereby second-generation (F2) embryos gestated (donor-in-recipient) in either a control (Cont-in-Cont, Rest-in-Cont) or restricted (Cont-in-Rest, Rest-in-Rest) mother. In male and female offspring, glomerular number and size were measured at postnatal day (PN) 35, and systolic blood pressure, glucose control, insulin sensitivity, and pancreatic β-cell mass were measured in separate sibling cohorts at 6 mo. Rest-in-Rest offspring were hypothesized to have similar characteristics (reduced growth, altered metabolic control, and hypertension) to non-embryo-transferred Rest, such that embryo transfer would not be a confounding experimental influence. However, embryo-transferred Rest-in-Rest offspring underwent accelerated growth during the peripubertal phase, followed by slowed growth between 2 and 3 mo of age compared with non-embryo-transferred Rest groups. Furthermore, renal function and insulin response to a glucose load were different to respective non-embryo-transferred groups. Our data demonstrate the long-term effects of in vitro embryo manipulation, which confounded the utility of this approach in delineating between the maternal pregnancy environment and germ line effects that drive transgenerational outcomes.

Early postweaning exercise improves central leptin sensitivity in offspring of rat dams fed high-fat diet during pregnancy and lactation

Maternal high-fat (HF) diet has long-term consequences on the metabolic phenotype of the offspring. Here, we determined the effects of postweaning exercise in offspring of rat dams fed HF diet during gestation and lactation. Pregnant Sprague-Dawley rats were maintained on chow or HF diet throughout gestation and lactation. All pups were weaned onto chow diet on postnatal day (PND) 21. At 4 wk of age, male pups were given free access to running wheels (RW) or remained sedentary (SED) for 3 wk, after which all rats remained sedentary, resulting in four groups: CHOW-SED, CHOW-RW, HF-SED, and HF-RW. Male HF offspring gained more body weight by PND7 compared with CHOW pups and maintained this weight difference through the entire experiment. Three weeks of postweaning exercise did not affect body weight gain in either CHOW or HF offspring, but reduced adiposity in HF offspring. Plasma leptin was decreased at the end of the 3-wk running period in HF-RW rats but was not different from HF-SED 9 wk after the exercise period ended. At 14 wk of age, intracerebroventricular injection of leptin suppressed food intake in CHOW-SED, CHOW-RW, and HF-RW, while it did not affect food intake in HF-SED group. At death, HF-RW rats also had higher leptin-induced phospho-STAT3 level in the arcuate nucleus than HF-SED rats. Both maternal HF diet and postweaning exercise had effects on hypothalamic neuropeptide and receptor mRNA expression in adult offspring. Our data suggest that postweaning exercise improves central leptin sensitivity and signaling in this model.

Can exercise training rescue the adverse cardiometabolic effects of low birth weight and prematurity?

Being born preterm and/or small for gestational age are well-established risk factors for cardiometabolic disease in adulthood. Physical activity has the potential to mitigate against the detrimental cardiometabolic effects of low birth weight from two perspectives: (i) maternal exercise prior to and during pregnancy; and (ii) exercise during childhood or adulthood for those born small or prematurely. Evidence from epidemiological birth cohort studies suggests that the effects of moderate-intensity physical activity during pregnancy on mean birth weight are small, but reduce the risk of either high or low birth weight infants. In contrast, vigorous and/or high-intensity exercise during pregnancy has been associated with reduced birth weight. In childhood and adolescence, exercise ability is compromised in extremely low birth weight individuals (< 1000 g), but only marginally reduced in those of very low to low birth weight (1000-2500 g). Epidemiological studies show that the association between birth weight and metabolic disease is lost in physically fit individuals and, consistently, that the association between low birth weight and metabolic syndrome is accentuated in unfit individuals. Physical activity intervention studies indicate that most cardiometabolic risk factors respond to exercise in a protective manner, independent of birth weight. The mechanisms by which exercise may protect low birth weight individuals include restoration of muscle mass, reduced adiposity and enhanced β-cell mass and function, as well as effects on both aerobic and anaerobic muscle metabolism, including substrate utilization and mitochondrial function. Vascular and cardiac adaptations are also likely important, but are less well studied.

Proactive Management of the Equine Athlete

Simple Summary

The athletic career of a horse is relatively short. Career length can be positively influenced by the trainer and the age at which the horse starts competition. There are opportunities for a team approach of health professionals and changes in management to improve functional/competition life. The ability to improve the tolerance of the tissue to exercise load via the introduction of early exercise, which reflects the horse’s evolutionary cursorial lifestyle, could provide a proactive mechanism to attenuate injury risk.

Abstract

Across many equestrian disciplines the median competition career of a horse is relatively short. One of the major reasons for short career length is musculoskeletal injury and a consistent variable is the trainer effect. There are significant opportunities within equestrian sport for a holistic approach to horse health to attenuate musculoskeletal injury. Proactive integration of care by health professionals could provide a mechanism to attenuate injury risk and the trainer effect. However, the limited data available on current exercise regimens for sport horses restricts interpretation of how management and exercise volume could be modified to reduce injury risk. Early exercise in the juvenile horse (i.e., pre weaning) has a positive effect on stimulating the musculoskeletal system and primes the horse for an athletic career. The early introduction to sport competition has also been identified to have a positive effect on career length. These data indicate that management systems reflecting the cursorial evolution of the horse may aid in attenuating loss from sport due to musculoskeletal injury.

Effects of glucocorticoids and exercise on pancreatic β-cell function and diabetes development

Peripheral insulin resistance and pancreatic β-cell dysfunction are hallmark characteristics of type 2 diabetes mellitus (T2DM). Several contributing factors have been proposed to promote these two defects in individuals with T2DM, including physical inactivity and chronic exposure to various psychosocial factors that increase the body's exposure to glucocorticoids, the main stress hormones in humans. Initially, β-cells have been shown to adapt to these stimuli, a phenomenon known as β-cell 'compensation'. However, long-term exposure to these physiologic and psychological stressors induces islet failure. Interestingly, glucocorticoids stimulate β-cell mass growth in parallel with promoting severe insulin resistance, the former being an important adaptive response to the latter. The direct relationship between glucocorticoids and β-cell dysfunction remains a controversial area of research. Elevations in circulating and/or tissue specific glucocorticoids have been associated with the development of obesity and T2DM in human and rodent models; however, the progression from insulin resistance to overt T2DM is highly disputed with respect to the in vivo and in vitro effects of glucocorticoids. Paradoxically, both intermittent physical stress and regular exercise alleviate insulin resistance and help to preserve β-cell mass, potentially by lowering glucocorticoid levels. Recent studies have begun to examine the mechanisms of intermittent and chronic glucocorticoid exposure and regular exercise in altering β-cell function. This review highlights recent discoveries on the physiological regulation of β-cells and diabetes development in conditions of elevated glucocorticoids, regular exercise and intermittent stress.

Effect of pregnancy for females born small on later life metabolic disease risk

There is a strong inverse relationship between a females own birth weight and her subsequent risk for gestational diabetes with increased risk of developing diabetes later in life. We have shown that growth restricted females develop loss of glucose tolerance during late pregnancy with normal pancreatic function. The aim of this study was to determine whether growth restricted females develop long-term impairment of metabolic control after an adverse pregnancy adaptation. Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (Restricted) or sham surgery (Control) in late pregnancy (E18) in F0 female rats. F1 Control and Restricted female offspring were mated with normal males and allowed to deliver (termed Ex-Pregnant). Age-matched Control and Restricted Virgins were also studied and glucose tolerance and insulin secretion were determined. Pancreatic morphology and hepatic glycogen and triacylglycerol content were quantified respectively. Restricted females were born lighter than Control and remained lighter at all time points studied (p<0.05). Glucose tolerance, first phase insulin secretion and liver glycogen and triacylglycerol content were not different across groups, with no changes in β-cell mass. Second phase insulin secretion was reduced in Restricted Virgins (-34%, p<0.05) compared to Control Virgins, suggestive of enhanced peripheral insulin sensitivity but this was lost after pregnancy. Growth restriction was associated with enhanced basal hepatic insulin sensitivity, which may provide compensatory benefits to prevent adverse metabolic outcomes often associated with being born small. A prior pregnancy was associated with reduced hepatic insulin sensitivity with effects more pronounced in Controls than Restricted. Our data suggests that pregnancy ameliorates the enhanced peripheral insulin sensitivity in growth restricted females and has deleterious effects for hepatic insulin sensitivity, regardless of maternal birth weight.

Maternal moderate physical training during pregnancy attenuates the effects of a low-protein diet on the impaired secretion of insulin in rats: potential role for compensation of insulin resistance and preventing gestational diabetes mellitus

The effects of pregestational and gestational low-to-moderate physical training on insulin secretion in undernourished mothers were evaluated. Virgin female Wistar rats were divided into four groups as follows: control (C, n = 5); trained (T, n = 5); low-protein diet (LP, n = 5); trained with a low-protein diet (T + LP, n = 5). Trained rats ran on a treadmill over a period of 4 weeks before mate (5 days week⁻¹ and 60 min day⁻¹, at 65% of VO_2max). At pregnancy, the intensity and duration of the exercise were reduced. Low-protein groups were provided with an 8% casein diet, and controls were provided with a 17% casein diet. At third day after delivery, mothers and pups were killed and islets were isolated by collagenase digestion of pancreas and incubated for a further 1 h with medium containing 5.6 or 16.7 mM glucose. T mothers showed increased insulin secretion by isolated islets incubated with 16.7 mM glucose, whereas LP group showed reduced secretion of insulin by isolated islets when compared with both C and LP + T groups. Physical training before and during pregnancy attenuated the effects of a low-protein diet on the secretion of insulin, suggesting a potential role for compensation of insulin resistance and preventing gestational diabetes mellitus.

Pregnancy in aged rats that were born small: cardiorenal and metabolic adaptations and second-generation fetal growth

Uteroplacental insufficiency is associated with adult cardiorenal and metabolic diseases, particularly in males. Pregnancy is the greatest physiological challenge facing women, and those born small are at increased risk of gestational hypertension and diabetes and delivering smaller babies. Increased maternal age is associated with exacerbated pregnancy complications. We hypothesized that pregnancy in aged, growth-restricted females unmasks an underlying predisposition to cardiorenal and metabolic dysfunction and compromises fetal growth. Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (restricted group) or sham surgery (control group) on d 18 of gestation in Wistar Kyoto rats. At 12 mo, growth-restricted F1 female offspring were mated with a normal male. F1 restricted females had elevated systolic blood pressure, before and during pregnancy (+10 mmHg) but normal renal and metabolic pregnancy adaptations. F2 fetal weight was not different between groups. In control and restricted females, advanced maternal age (12 vs. 4 mo) was associated with a reduction in the hypoglycemic response to pregnancy and reduced F2 fetal litter size and body weight. Aged rats born small exhibited mostly normal pregnancy adaptations, although they had elevated blood pressure. Advanced maternal age was associated with poorer fetal outcomes that were not exacerbated by low maternal birth weight.

Exercise early in life in rats born small does not normalize reductions in skeletal muscle PGC-1α in adulthood

We have previously shown that 4 wk of exercise training early in life normalizes the otherwise greatly reduced pancreatic β-cell mass in adult male rats born small. The aim of the current study was to determine whether a similar normalization in adulthood of reduced skeletal muscle mitochondrial biogenesis markers and alterations in skeletal muscle lipids of growth-restricted male rats occurs following early exercise training. Bilateral uterine vessel ligation performed on day 18 of gestation resulted in Restricted offspring born small (P < 0.05) compared with both sham-operated Controls and a sham-operated Reduced litter group. Offspring remained sedentary or underwent treadmill running from 5-9 (early exercise) or 20-24 (later exercise) wk of age. At 24 wk of age, Restricted and Reduced litter offspring had lower (P < 0.05) skeletal muscle peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) protein expression compared with Control offspring. Early exercise training had the expected effect of increasing skeletal muscle markers of mitochondrial biogenesis, but, at this early age (9 wk), there was no deficit in Restricted and Reduced litter skeletal muscle mitochondrial biogenesis. Unlike our previous observations in pancreatic β-cell mass, there was no "reprogramming" effect of early exercise on adult skeletal muscle such that PGC-1α was lower in adult Restricted and Reduced litter offspring irrespective of exercise training. Later exercise training increased mitochondrial biogenesis in all groups. In conclusion, although the response to exercise training remains intact, early exercise training in rats born small does not have a reprogramming effect to prevent deficits in skeletal muscle markers of mitochondrial biogenesis in adulthood.

Cardio-renal and metabolic adaptations during pregnancy in female rats born small: implications for maternal health and second generation fetal growth

Intrauterine growth restriction caused by uteroplacental insufficiency increases risk of cardiovascular and metabolic disease in offspring. Cardio-renal and metabolic responses to pregnancy are critical determinants of immediate and long-term maternal health. However, no studies to date have investigated the renal and metabolic adaptations in growth restricted offspring when they in turn become pregnant. We hypothesised that the physiological challenge of pregnancy in growth restricted females exacerbates disease outcome and compromises next generation fetal growth. Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (Restricted) or sham surgery (Control) on day 18 of gestation in WKY rats and F1 female offspring birth and postnatal body weights were recorded. F1 Control and Restricted females were mated at 4 months and blood pressure, renal and metabolic parameters were measured in late pregnancy and F2 fetal and placental weights recorded. Age-matched non-pregnant Control and Restricted F1 females were also studied. F1 Restricted females were born 10-15% lighter than Controls. Basal insulin secretion and pancreatic β-cell mass were reduced in non-pregnant Restricted females but restored in pregnancy. Pregnant Restricted females, however, showed impaired glucose tolerance and compensatory glomerular hypertrophy, with a nephron deficit but normal renal function and blood pressure. F2 fetuses from Restricted mothers exposed to physiological measures during pregnancy were lighter than Controls highlighting additive adverse effects when mothers born small experience stress during pregnancy. Female rats born small exhibit mostly normal cardio-renal adaptations but altered glucose control during late pregnancy making them vulnerable to lifestyle challenges.