Effects of hypothyroidism on the structure and mechanical properties of bone in the ovine fetus

Hormonal Determinants of Growth and Weight Gain in the Human Fetus and Preterm Infant

The factors controlling linear growth and weight gain in the human fetus and newborn infant are poorly understood. We review here the changes in linear growth, weight gain, lean body mass, and fat mass during mid- and late gestation and the early postnatal period in the context of changes in the secretion and action of maternal, placental, fetal, and neonatal hormones, growth factors, and adipocytokines. We assess the effects of hormonal determinants on placental nutrient delivery and the impact of preterm delivery on hormone expression and postnatal growth and metabolic function. We then discuss the effects of various maternal disorders and nutritional and pharmacologic interventions on fetal and perinatal hormone and growth factor production, growth, and fat deposition and consider important unresolved questions in the field.

Thyroid hormones: Metabolism and transportation in the fetoplacental unit

The thyroid hormones (THs), thyroxine (T4) and triiodothyronine (T3), are of vital importance for fetal development. The concentration of THs in fetal circulation varies throughout gestation and differs from the concentration in the maternal serum, indicating the presence of maternal-fetal thyroid homeostasis regulatory mechanisms in the placenta. The passage of THs from maternal circulation to fetal circulation is modulated by plasma membrane transporters, enzymes, and carrier proteins. Monocarboxylate transporter 8, iodothyronine deiodinases (DIO2 and DIO3), and transthyretin are especially involved in this maternal-fetal thyroid modulation, shown by a greater expression in the placenta. THs also play a role in placental development and as expected, abnormal variations in TH levels are associated with pregnancy complications and can result in damage to the fetus. Although new evidence regarding TH regulation during pregnancy and its effects in the mother, placenta, and fetus has been published, many aspects of these interactions are still poorly understood. The objective of this review is to provide an evidence-based update, drawn from current data, on the metabolism and transport of THs in the placenta and their vital role in the maternal-fetal relationship.

Adaptive Responses of Thyroid Hormones, Insulin, and Glucose during Pregnancy and Lactation in Dairy Cows

The study examined the effects of different stages of pregnancy and lactation on thyroid, insulin, and glucose responses in dairy cows. In the present study, 30 dairy cows (10 Holstein, 10 Simmental, and 10 Brown) at 30 ± 20 d of lactation were randomly selected and blood samples were collected once every 60 d for one year to measure circulating thyroid stimulating hormone (TSH), total and free triiodothyronines (T3, fT3) and thyroxines (T4, fT4), insulin, and glucose. Pregnant cows showed higher T4 (p = 0.010) and insulin (p = 0.046) concentrations at >180 d than at >60−120 d of pregnancy and in nonpregnant cows. Along the lactation phase, circulating T4 concentrations showed a biphasic trend, decreasing from 0−60 d to >60−120 d phase, which showed the lowest values, and then increasing until the end of lactation (>300 d) (p = 0.016). Glucose showed the highest concentrations at the start of lactation (0−120 days) and the lowest values at the end (p = 0.008). The monitoring of thyroid hormones, insulin, and glucose changes represents an important tool to evaluate the anabolic and/or catabolic adaptation in response to functional periods in dairy cows, which can potentially predispose the cows to an excessive negative energy balance and related metabolic issues.

Pancreas deficiency modifies bone development in the ovine fetus near term

Hormones have an important role in the regulation of fetal growth and development, especially in response to nutrient availability in utero. Using micro-CT and an electromagnetic three-point bend test, this study examined the effect of pancreas removal at 0.8 fraction of gestation on the developing bone structure and mechanical strength in fetal sheep. When fetuses were studied at 10 and 25 days after surgery, pancreatectomy caused hypoinsulinaemia, hyperglycaemia and growth retardation which was associated with low plasma concentrations of leptin and a marker of osteoclast activity and collagen degradation. In pancreatectomized fetuses compared to control fetuses, limb lengths were shorter, and trabecular (Tb) bone in the metatarsi showed greater bone volume fraction, Tb thickness, degree of anisotropy and porosity, and lower fractional bone surface area and Tb spacing. Mechanical strength testing showed that pancreas deficiency was associated with increased stiffness and a greater maximal weight load at fracture in a subset of fetuses studied near term. Overall, pancreas deficiency in utero slowed the growth of the fetal skeleton and adapted the developing bone to generate a more compact and connected structure. Maintenance of bone strength in growth-retarded limbs is especially important in a precocial species in preparation for skeletal loading and locomotion at birth.

Maternal nutrient restriction alters thyroid hormone dynamics in placentae of sheep having small for gestational age fetuses

Thyroid hormones regulate a multitude of metabolic and cellular processes involved in placental and fetal growth, while maternal nutrient restriction (NR) has the potential to influence these processes. Those fetuses most impacted by NR, as categorized by weight, are termed small for gestational age (SGA), but the role of thyroid hormones in these pregnancies is not fully understood. Therefore, the aims of the present study were to determine effects of NR during pregnancy on maternal and fetal thyroid hormone concentrations, as well as temporal and cell-specific expression of mRNAs and proteins for placental thyroid hormone transporters, thyroid hormone receptors, and deiodinases in ewes having either SGA or normal weight fetuses. Ewes with singleton pregnancies were fed either a 100% NRC (n = 8) or 50% NRC (NR; n = 28) diet from Days 35 to 135 of pregnancy with a single placentome surgically collected on Day 70. Fetal weight at necropsy on Day 135 was used to designate the fetuses as NR NonSGA (n = 7; heaviest NR fetuses) or NR SGA (n = 7; lightest NR fetuses). Thyroid hormone levels were lower in NR SGA compared to NR NonSGA ewes, while all NR fetuses had lower concentrations of thyroxine at Day 135. Expression of mRNAs for thyroid hormone transporters SLC16A2, SLC16A10, SLCO1C1, and SLCO4A1 were altered by day, but not nutrient restriction. Expression of THRA mRNA and protein was dysregulated in NR SGA fetuses with protein localized to syncytial and stromal cells in placentomes in all groups. The ratio of deiodinases DIO2 and DIO3 was greater for NR SGA placentae at Day 70, while DIO3 protein was less abundant in placentae from NR SGA than 100% NRC ewes. These results identify mid-gestational modifications in thyroid hormone-associated proteins in placentomes of ewes having SGA fetuses, as well as a potential for placentomes from NonSGA pregnancies to adapt to, and overcome, nutritional restrictions during pregnancy.

Effect of Subclinical and Overt Form of Rat Maternal Hypothyroidism on Offspring Endochondral Bone Formation

Maternal hypothyroidism in its overt form affects skeletal development of the offspring, but these data are not available for the subclinical form which is becoming very frequent among pregnant women. We hypothesized that the subclinical form of hypothyroidism in rat dams, infl uences the process of offspring endochondral ossifi cation affecting proliferation and differentiation of chondrocytes, osteoclasts and osteoblasts in pups. Seven-day-old male pups (n=18) derived from control dams and dams treated with a low dose (1.5 mg/L) or high dose (150 mg/L) of propylthiouracil in drinking water during pregnancy and lactation were used. Histomorphometric analysis of pups’ tibia proximal growth plate, expression of mRNA, immunohistochemical and histochemical visualization of extracellular matrix components was performed. The length of the tibia was reduced in hypothyroid pups. Secretion of type 2 and 10 collagens in the subclinical and overt form were lower while the amount of glycosaminoglycans was higher when compared with controls. Down-regulated tartrate resistant acid phosphatase mRNA indicated altered osteoclasts function while lower expression of dentin matrix acid protein-1 mRNA and reduced synthesis of type 1 collagen accentuated a compromised bone formation in the overt form of hypothyroidism. The subclinical form of maternal hypothyroidism had a negative effect on the differentiation of hypertrophic chondrocytes and calcifi ed cartilage removal in 7-day-old pups. In addition, overt hypothyroidism had a negative effect on the proliferation of chondrocytes and deposition of osteoid. Both forms of hypothyroidism resulted in a decrease of tibia length due to changes in growth plate formation.

Subclinical Changes in Maternal Thyroid Function Parameters in Pregnancy and Fetal Growth

CONTEXT

Overt thyroid disease in pregnancy is a known risk factor for abnormal fetal growth and development. Data on the effects of milder forms of variation in maternal thyroid function on intrauterine growth are less well examined.

OBJECTIVE

We explored these associations using repeated thyroid hormone and ultrasound measurements.

DESIGN, SETTING, AND PARTICIPANTS

Data were obtained from 439 pregnant women without diagnosed thyroid disease who were participants in a case-control study of preterm birth nested within an ongoing prospective birth cohort in Boston, Massachusetts.

MAIN OUTCOME MEASURES

Ultrasound and delivery indices of fetal growth were standardized to those measured in a larger population.

RESULTS

At median 10, 18, and 26 weeks of gestation, we observed significant inverse associations between free thyroxine (FT4) and birth weight z scores, with the strongest association detected at median 10 weeks, at which time a 10% increase in FT4 was associated with a 0.02 z score decrease (∼8.5 g) in birth weight (β = -0.41 for ln-transformed FT4; 95% confidence interval, -0.64 to -0.18). FT4 was also inversely associated with repeated measurements of estimated fetal weight, head circumference, and abdominal circumference. We observed weaker inverse associations for total T4 and a positive relationship between total triiodothyronine and birth weight z scores. We did not observe any associations for thyroid-stimulating hormone.

CONCLUSION

In pregnant women without overt thyroid disease, subclinical changes in thyroid function parameters may influence fetal growth.

Sex- and bone-specific responses in bone structure to exogenous leptin and leptin receptor antagonism in the ovine fetus

Widespread expression of leptin and its receptor in developing cartilage and bone suggests that leptin may regulate bone growth and development in the fetus. Using microcomputed tomography, this study investigated the effects of exogenous leptin and leptin receptor antagonism on aspects of bone structure in the sheep fetus during late gestation. From 125 to 130 days of gestation (term ~145 days), chronically catheterized singleton sheep fetuses were infused intravenously for 5 days with either saline (0.9% saline, n = 13), recombinant ovine leptin at two doses (0.6 mg·kg^-1·day^-1 LEP1, n = 10 or 1.4 mg·kg^-1·day^-1 LEP2, n = 7), or recombinant superactive ovine leptin receptor antagonist (4.6 mg·kg^-1·day^-1 SOLA, n = 6). No significant differences in plasma insulin-like growth factor-I, osteocalcin, calcium, inorganic phosphate, or alkaline phosphatase were observed between treatment groups. Total femur midshaft diameter and metatarsal lumen diameter were narrower in male fetuses treated with exogenous leptin. In a fixed length of femur midshaft, total and bone volumes were reduced by the higher dose of leptin; nonbone space volume was lower in both groups of leptin-treated fetuses. Leptin infusion caused increments in femur porosity and connectivity density, and vertebral trabecular thickness. Leptin receptor antagonism decreased trabecular spacing and increased trabecular number, degree of anisotrophy, and connectivity density in the lumbar vertebrae. The increase in vertebral porosity observed following leptin receptor antagonism was greater in the malecompared with female, fetuses. Therefore, leptin may have a role in the growth and development of the fetal skeleton, dependent on the concentration of leptin, sex of the fetus, and bone type examined.

Hypothyroidism in utero stimulates pancreatic beta cell proliferation and hyperinsulinaemia in the ovine fetus during late gestation

Key points

Thyroid hormones are important regulators of growth and maturation before birth, although the extent to which their actions are mediated by insulin and the development of pancreatic beta cell mass is unknown.

Hypothyroidism in fetal sheep induced by removal of the thyroid gland caused asymmetric organ growth, increased pancreatic beta cell mass and proliferation, and was associated with increased circulating concentrations of insulin and leptin.

In isolated fetal sheep islets studied in vitro, thyroid hormones inhibited beta cell proliferation in a dose‐dependent manner, while high concentrations of insulin and leptin stimulated proliferation.

The developing pancreatic beta cell is therefore sensitive to thyroid hormone, insulin and leptin before birth, with possible consequences for pancreatic function in fetal and later life.

The findings of this study highlight the importance of thyroid hormones during pregnancy for normal development of the fetal pancreas.

Abstract

Development of pancreatic beta cell mass before birth is essential for normal growth of the fetus and for long‐term control of carbohydrate metabolism in postnatal life. Thyroid hormones are also important regulators of fetal growth, and the present study tested the hypotheses that thyroid hormones promote beta cell proliferation in the fetal ovine pancreatic islets, and that growth retardation in hypothyroid fetal sheep is associated with reductions in pancreatic beta cell mass and circulating insulin concentration in utero. Organ growth and pancreatic islet cell proliferation and mass were examined in sheep fetuses following removal of the thyroid gland in utero. The effects of triiodothyronine (T₃), insulin and leptin on beta cell proliferation rates were determined in isolated fetal ovine pancreatic islets in vitro. Hypothyroidism in the sheep fetus resulted in an asymmetric pattern of organ growth, pancreatic beta cell hyperplasia, and elevated plasma insulin and leptin concentrations. In pancreatic islets isolated from intact fetal sheep, beta cell proliferation in vitro was reduced by T₃ in a dose‐dependent manner and increased by insulin at high concentrations only. Leptin induced a bimodal response whereby beta cell proliferation was suppressed at the lowest, and increased at the highest, concentrations. Therefore, proliferation of beta cells isolated from the ovine fetal pancreas is sensitive to physiological concentrations of T₃, insulin and leptin. Alterations in these hormones may be responsible for the increased beta cell proliferation and mass observed in the hypothyroid sheep fetus and may have consequences for pancreatic function in later life.

Thyroid hormones are important regulators of growth and maturation before birth, although the extent to which their actions are mediated by insulin and the development of pancreatic beta cell mass is unknown.

Hypothyroidism in fetal sheep induced by removal of the thyroid gland caused asymmetric organ growth, increased pancreatic beta cell mass and proliferation, and was associated with increased circulating concentrations of insulin and leptin.

In isolated fetal sheep islets studied in vitro, thyroid hormones inhibited beta cell proliferation in a dose‐dependent manner, while high concentrations of insulin and leptin stimulated proliferation.

The developing pancreatic beta cell is therefore sensitive to thyroid hormone, insulin and leptin before birth, with possible consequences for pancreatic function in fetal and later life.

The findings of this study highlight the importance of thyroid hormones during pregnancy for normal development of the fetal pancreas.

Prenatal origins of postnatal variation in growth, development and productivity of ruminants

This review provides an update on recent research into the effects of maternal nutrition on fetal biology and the growth, development and productivity of progeny in postnatal life of ruminant livestock. Evidence is summarised for effects on postnatal growth and body composition, feed intake and efficiency, carcass characteristics and meat quality, wool production, reproduction and lactation performance. In general, these demonstrated effects are not large in relation to the effects of postnatal nutrition and other environmental influences. The mechanisms underpinning the above production outcomes are briefly discussed in terms of systemic endocrine and metabolic responses, and cellular and molecular effects in skeletal muscle, bone, adipose tissue, wool follicles and brain of fetal, neonatal and adult progeny. Treatments observed to elicit tissue responses include maternal under- and overnutrition at various stages of pregnancy and placental insufficiency caused by increased litter size, chronic maternal heat stress and premating carunclectomy in sheep. The as yet meagre evidence for epigenetic mediation of intergenerational effects in ruminants is considered, as is the likelihood that other, more conventional explanations may suffice in some cases. Finally, evidence is summarised for the proposition that the placenta is not merely a passive conduit for nutrient transfer from dam to fetus, but plays an active role in buffering the effects of variations in maternal nutrition on fetal growth and development, and thence, postnatal outcomes.

Redistribution of body composition in patients with Graves' disease after iodine-131 treatment

OBJECTIVE

The objective of this study was to investigate body composition redistribution at 3 months after radioactive iodine therapy (RAI).

METHODS

Eighty patients with Graves' disease (GD) for RAI and 18 volunteers were recruited. All patients underwent thyroid status test and dual-energy x-ray absorptiometry at baseline and 3 months after RAI. According to the second thyroid status test, patients were divided into the following groups: A, with aggravated hyperthyroidism; B-1, with improved hyperthyroidism; B-2, with euthyroidism; and B-3, with hypothyroidism.

RESULTS

Total lean mass (LM) but fat mass (FM) and bone mineral content (BMC) of whole GD patients after RAI recovered to be not different with controls. Compared with baseline, in group A, FM in the left leg increased, and LM in left arm, right arm, trunk and total LM decreased (P<0.05). In B-2, FM in the head increased, and LM in the head, right arm, trunk and total LM increased (P<0.05). In B-3, FM in the right leg and total body fat percentage decreased, but FM in the head, android-to-gynoid fat ratio and body mass index increased (P<0.05); LM of all sites, weight and total mass increased (P<0.05); BMC in lumbar spine and left leg, and total BMC decreased (P<0.05). Body composition of unmentioned sites was retained after RAI in each group (P>0.05).

CONCLUSIONS

Replenishment of LM gets priority rather than FM and BMC during the first 3 months after RAI, and the increase in LM starts from the upper body; head is the regional site in which FM recovery occurs first.

Thyroid hormones in fetal growth and prepartum maturation

The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are essential for normal growth and development of the fetus. Their bioavailability in utero depends on development of the fetal hypothalamic-pituitary-thyroid gland axis and the abundance of thyroid hormone transporters and deiodinases that influence tissue levels of bioactive hormone. Fetal T4 and T3 concentrations are also affected by gestational age, nutritional and endocrine conditions in utero, and placental permeability to maternal thyroid hormones, which varies among species with placental morphology. Thyroid hormones are required for the general accretion of fetal mass and to trigger discrete developmental events in the fetal brain and somatic tissues from early in gestation. They also promote terminal differentiation of fetal tissues closer to term and are important in mediating the prepartum maturational effects of the glucocorticoids that ensure neonatal viability. Thyroid hormones act directly through anabolic effects on fetal metabolism and the stimulation of fetal oxygen consumption. They also act indirectly by controlling the bioavailability and effectiveness of other hormones and growth factors that influence fetal development such as the catecholamines and insulin-like growth factors (IGFs). By regulating tissue accretion and differentiation near term, fetal thyroid hormones ensure activation of physiological processes essential for survival at birth such as pulmonary gas exchange, thermogenesis, hepatic glucogenesis, and cardiac adaptations. This review examines the developmental control of fetal T4 and T3 bioavailability and discusses the role of these hormones in fetal growth and development with particular emphasis on maturation of somatic tissues critical for survival immediately at birth.

Hormonal and nutritional drivers of intrauterine growth

PURPOSE OF REVIEW

Size at birth is critical in determining life expectancy with both small and large neonates at risk of shortened life spans. This review examines the hormonal and nutritional drivers of intrauterine growth with emphasis on the role of foetal hormones as nutritional signals in utero.

RECENT FINDINGS

Nutrients drive intrauterine growth by providing substrate for tissue accretion, whereas hormones regulate nutrient distribution between foetal oxidative metabolism and mass accumulation. The main hormonal drivers of intrauterine growth are insulin, insulin-like growth factors and thyroid hormones. Together with leptin and cortisol, these hormones control cellular nutrient uptake and the balance between accretion and differentiation in regulating tissue growth. They also act indirectly via the placenta to alter the materno-foetal supply of nutrients and oxygen. By responding to nutrient and oxygen availability, foetal hormones optimize the survival and growth of the foetus with respect to its genetic potential, particularly during adverse conditions. However, changes in the intrauterine growth of individual tissues may alter their function permanently.

SUMMARY

In both normal and compromised pregnancies, intrauterine growth is determined by multiple hormonal and nutritional drivers which interact to produce a specific pattern of intrauterine development with potential lifelong consequences for health.

Oral tori are associated with local mechanical and systemic factors: a case-control study

PURPOSE

To estimate if various dental factors, medications, and medical conditions are associated with an increased risk for the presence of oral tori.

MATERIALS AND METHODS

Using a case-control study design, the investigators identified and adjudicated a sample of cases with torus palatinus (TP) and/or torus mandibularis (TM) during a 1.5-year period. The medical records were abstracted and data on dental factors, temporomandibular dysfunction (TMD), medications, and medical conditions were recorded. Risk estimates were calculated as adjusted odds ratios (AORs) with 95% confidence intervals (CIs) using conditional logistic regression analyses, and the P value was set at .05.

RESULTS

The sample was composed of 66 subjects with TM, 34 subjects with TP, and 100 control subjects from the same database. Any form of oral torus (TP and/or TM) was associated significantly with TMD (AOR, 10.51; 95% CI, 4.46 to 24.78; P<.01) and tooth attrition (AOR, 5.22; 95% CI, 2.32 to 11.77; P<.01). TP was associated significantly with TMD (AOR, 4.14; 95% CI, 1.21 to 14.21; P<.05), tooth attrition (AOR, 38.18; 95% CI, 7.20 to 202.41; P<.01), and treated hypertension (AOR, 6.64; 95% CI, 1.31 to 33.57; P<.05). TM was associated significantly with TMD (AOR, 5.77; 95% CI, 2.38 to 13.98; P<.01), tooth attrition (AOR, 6.69; 95% CI, 2.78 to 16.14; P<.01), and a penicillin allergy (AOR, 4.45; 95% CI, 1.05 to 18.83; P<.05).

CONCLUSIONS

This study provides clinical evidence showing significant associations between oral tori and various dental factors, medications, and medical conditions. These findings add to the list of environmental factors believed to contribute to the formation of oral tori.