Revisiting early hypothyroidism screening in infants with Down syndrome.

OBJECTIVE: To identify if the incidence of hypothyroidism in infants with Down syndrome is higher than previous childhood estimates (15%) when examined prior to the standard retesting at 6 months of age. STUDY DESIGN: A retrospective observational cohort study of 122 children with Down syndrome admitted to a university-based birthing hospital between May 2000 and March 2012. Demographic data (for example, date of birth, gender, gestational age, inborn) and diagnostic data (Down syndrome, congenital heart disease and gastrointestinal disease) were cross-linked with thyroid hormone laboratory tests (total thyroxine, free thyroxine and thyroid stimulating hormone) to determine incidence of identified hypothyroidism and thyroid testing prior to 4 months of age (n=80). RESULT: In all, 32.5% were found to have any hypothyroidism. Of these, 14 were primary hypothyroidism (17.5%) needing supplemental T4 therapy, 12 were compensated hypothyroidism (15%) and euthyroid was identified in 54 infants (67.5%). CONCLUSION: Despite normal newborn screens, the incidence of any hypothyroidism (early compensated hypothyroidism and primary hypothyroidism) was higher than previously reported.

Effect of prenatal glucocorticoid on fetal lung ultrastructural maturation in hyt/hyt mice with primary hypothyroidism.

Glucocorticoids (GC) and thyroid hormones (TH) accelerate fetal lung maturation. Though GC are used clinically, the mechanisms of GC-induced fetal lung maturity remain unclear. Prenatal GC increase fetal TH activity in humans and in animals. Thus, it is possible that increased fetal TH activity after prenatal GC plays a role in accelerating fetal lung maturation. However, this hypothesis has remained untested due to the lack of a suitable animal model. In the hyt/hyt mouse primary hypothyroidism occurs due to a point mutation in the beta subunit of the thyroid-stimulating hormone receptor of the thyroid gland, and it is transmitted in an autosomal recessive manner. We studied the effect of maternal betamethasone on fetal lung ultrastructure in hyt/hyt (hypothyroid) and Balb-c (euthyroid) mice. Hypothyroid mice were made euthyroid by T3 supplementation and mated to carry hypothyroid pups. Vehicle (n = 6) or betamethasone (n = 6) was injected intraperitoneally twice daily into the doe on days 16 and 17 of gestation. Fetal lungs on 18 days of gestation were subjected to ultrastructural morphometric analysis. The number of lamellar bodies per type II cell increased after betamethasone in Balb-c (2.10+/-0.31 vs. 3.43+/-0.37) and hyt/hyt (0.77+/-0.28 vs. 3.85+/-0.26) mice. The alveolar-to-parenchymal ratio was less in the vehicle-treated hyt/hyt (0.082+/-0.024) as compared with the vehicle-treated Balb-c (0.30+/-0.05) mice, while prenatal betamethasone increased the alveolar-to-parenchymal ratio in the hyt/hyt (0.227+/-0.034) but not in the Balb-c (0.26+/-0.04) mice. The glycogen-to-nucleus ratio was higher in betamethasone-treated hyt/hyt mice (1.46+/-0.20) when compared to vehicle-treated hyt/hyt (0.89+/-0.14) or Balb-c (1.01+/-0.17) or betamethasone-treated Balb-c (0.81+/-0.13) mice. Though tubular myelin was readily apparent in the airspace lumen of betamethasone-treated Balb-c mice, it was absent in betamethasone-treated hyt/hyt fetal lungs. We conclude that fetal thyroid plays an important role in accelerating some aspects of fetal lung ultrastructural maturation from GC stimulation.

Effect of primary congenital hypothyroidism upon expression of genes mediating murine brain glucose uptake.

Using hyt/hyt mice that exhibit naturally occurring primary hypothyroidism (n = 72) and Balb/c controls (n = 66), we examined the mRNA, protein, and activity of brain glucose transporters (Glut 1 and Glut 3) and hexokinase I enzyme at various postnatal ages (d 1, 7, 14, 21, 35, and 60). The hyt/hyt mice showed an age-dependent decline in body weight (p < 0.04) and an increase in serum TSH levels (p < 0.001) at all ages. An age-dependent translational/posttranslational 40% decline in Glut 1 (p = 0.02) with no change in Glut 3 levels was observed. These changes were predominant during the immediate neonatal period (d 1). A posttranslational 70% increase in hexokinase enzyme activity was noted at d 1 alone (p < 0.05) with no concomitant change in brain 2-deoxy-glucose uptake. This was despite a decline in the hyt/hyt glucose production rate. We conclude that primary hypothyroidism causes a decline in brain Glut 1 associated with no change in Glut 3 levels and a compensatory increase in hexokinase enzyme activity. These changes are pronounced only during the immediate neonatal period and disappear in the postweaned stages of development. These hypothyroid-induced compensatory changes in gene products mediating glucose transport and phosphorylation ensure an adequate supply of glucose to the developing brain during transition from fetal to neonatal life.

Developmental regulation of genes mediating murine brain glucose uptake.

We examined the molecular mechanisms that mediate the developmental increase in murine whole brain 2-deoxyglucose uptake. Northern and Western blot analyses revealed an age-dependent increase in brain GLUT-1 (endothelial cell and glial) and GLUT-3 (neuronal) membrane-spanning facilitative glucose transporter mRNA and protein concentrations. Nuclear run-on experiments revealed that these developmental changes in GLUT-1 and -3 were regulated posttranscriptionally. In contrast, the mRNA and protein levels of the mitochondrially bound glucose phosphorylating hexokinase I enzyme were unaltered. However, hexokinase I enzyme activity increased in an age-dependent manner suggestive of a posttranslational modification that is necessary for enzymatic activation. Together, the postnatal increase in GLUT-1 and -3 concentrations and hexokinase I enzymatic activity led to a parallel increase in murine brain 2-deoxyglucose uptake. Whereas the molecular mechanisms regulating the increase in the three different gene products may vary, the age-dependent increase of all three constituents appears essential for meeting the increasing demand of the maturing brain to fuel the processes of cellular growth, differentiation, and neurotransmission.

Hypothyroidism delays fetal stratum corneum development in mice.

The epidermal permeability barrier, required for terrestrial life, is localized to lipid-enriched lamellar membranes in the extracellular spaces of the stratum corneum (SC). Immaturity of the SC is a significant contributor to morbidity and mortality in premature infants. Previous studies have shown that supraphysiologic concentrations of thyroid hormone accelerate epidermis/SC ontogenesis. Here we studied SC development in Hyt/Hyt mice who are genetically hypothyroid due to a mutation in the TSH receptor. In control mice on d 18 of gestation (term 19.5 d), only focal areas displayed a mature SC membrane pattern. By 19 d of gestation there was a mature multilayered SC with lamellar unit structures filling the extracellular spaces similar to that seen in mature mice. In Hyt/Hyt mice SC development was delayed at both 18 and 19 d of gestation. In both strains of mice, within the first day after birth there were no differences in epidermal or SC appearance, and the SC was fully mature. These findings indicate that thyroid hormone plays a physiologic role during normal intrauterine development of the SC. However, normal SC maturation ultimately occurs, indicating that thyroid hormone is not absolutely essential. Previous studies have shown that glucocorticoids accelerate SC development in euthyroid rats, and in the present study we demonstrate that glucocorticoids also accelerate SC ontogenesis in euthyroid mice. In contrast, in Hyt/Hyt mice glucocorticoids did not accelerate or normalize SC development, indicating that the glucocorticoid effect on SC maturation requires a euthyroid state or that glucocorticoids act via thyroid hormone. These studies demonstrate that thyroid hormone status is an important regulator of fetal SC development.

Thyrotropin-releasing hormone accelerates fetal mouse lung ultrastructural maturation via stimulation of extra thyroidal pathway.

Maternal administration of TSH-releasing hormone (TRH) in the euthyroid mouse accelerates fetal lung ultrastructural maturation. However, the mechanism(s) of TRH in fetal lung development remains unclear; it could be due to its neuroendocrine and/or neurotransmitter effects. Although the neuroendocrine effect of TRH is mediated via stimulation of the fetal pituitary-thyroid axis, the neurotransmitter effect is mediated via stimulation of fetal autonomic nervous system activity. In the hyt/hyt mouse there is a point mutation in the beta subunit of the TSH receptor in the thyroid gland of the Balb-c mouse. In these mice TSH does not bind to its receptors, leading ultimately to the development of primary hypothyroidism, which is transmitted as an autosomal recessive trait. A maturational delay in the lung ultrastructure of the hyt/hyt mouse fetus has been observed. This investigation was undertaken to study the effect of maternal TRH treatment on lung ultrastructural maturation in the hyt/hyt mouse fetus. If the effect of TRH is mediated via stimulation of fetal pituitary-thyroid axis, TRH treatment should not enhance lung maturity in the hyt/hyt fetus and vice versa. Adult hyt/hyt mice made euthyroid by triiodothyronine supplementation were mated to carry hyt/hyt pups. Saline or TRH (0.4 or 0.6 mg/kg/dose) was administered to the mother (i.p.) on d 16 and 17 (b.i.d.) and on d 18 of pregnancy 1 h before killing (term, approximately 20 d). The fetal lung electron micrographs were subjected to ultrastructural morphometric analysis of the number of lamellar bodies and glycogen/nuclear ratio in type II cells, and the alveolar/parenchymal ratio by Chalkley point counting with an interactive computerized image analyzer (Optimas, Bioscan). Fetal lungs exposed to the lower dose of TRH (n = 7) showed no significant difference in their ultrastructural maturation when compared with saline-treated controls (n = 5). However, fetal lungs exposed to a higher dose of TRH (n = 6) showed increased numbers of lamellar bodies per type II cell, an increase in the alveolar/parenchymal ratio, larger air spaces, thinner alveolar septa, presence of tubular myelin, and increased numbers of air-blood barriers. We conclude that the effect of TRH in accelerating fetal mouse lung maturation is at least in part mediated via stimulation of extra thyroidal pathways.

Fetal mouse lung ultrastructural maturation is accelerated by maternal thyrotropin-releasing hormone treatment.

Maternal administration of thyrotropin-releasing hormone, alone or in combination with corticosteroid, accelerates functional, morphologic and biochemical fetal lung maturation. However, the dose-response relationship of maternal thyrotropin-releasing hormone treatment and acceleration of fetal lung ultrastructural maturation or disaturated phosphatidylcholine content has not been investigated. We administered (i.p.) saline or thyrotropin-releasing hormone (0.2, 0.4 or 0.6 mg/kg/dose) to the pregnant Balb/c mouse on days 16 and 17 (b.i.d.) and on day 18 of gestation (1 h prior to killing). Morphometric ultrastructural analysis and quantitation of disaturated phosphatidylcholine content was done on the 18-day gestation fetal lung. Maternal thyrotropin-releasing hormone treatment resulted in an increase in the number of lamellar bodies and depletion of glycogen in fetal lung type II cells, and an increase in the lung airspace to parenchymal ratio. In addition, a striking difference in the pattern of lung growth was noted in the thyrotropin-releasing-hormone-treated (0.4 and 0.6 mg/kg/dose) groups. These lungs had larger air spaces, thinner alveolar septae and more air-blood barriers. Maternal thyrotropin-releasing hormone treatment did not influence fetal lung disaturated phosphatidylcholine content. We conclude that in the mouse, maternal thyrotropin-releasing hormone treatment enhances fetal lung structural maturation and propose that thyrotropin-releasing hormone plays a role in mammalian fetal lung growth.

Expression of genes involved in placental glucose uptake and transport in the nonobese diabetic mouse pregnancy.

OBJECTIVE: Maternal diabetes alters placental glucose metabolism and maternofetal glucose transport. The purpose of this study was to determine whether genes involved in placental glucose uptake and transport were concomitantly altered, resulting in the observed changes in the state of maternal diabetes. STUDY DESIGN: By means of the nonobese diabetic pregnant mouse we examined the expression of placental glucose transporters, hexokinase I, glycogen content, glycogen-regulating enzyme activities in control animals (blood glucose 8.5 +/- 0.2 mmol/L, n = 25), moderate maternal diabetes (blood glucose 10 to 13.9 mmol/L, n = 16), and severe maternal diabetes (blood glucose > 16.7 mmol/L, n = 12). Comparisons by the analysis of variance and the Newman-Keuls test were performed. RESULTS: Although changes in placental glucose transporters and hexokinase I messenger ribonucleic acid levels occurred, neither state of diabetes altered the corresponding protein levels. Changes in placental deoxyribonucleic acid (p < 0.05) and glycogen content (p < 0.01), fetal insulin levels (p < 0.02), and fetal size (p < 0.05) occurred in the moderately diabetic group, and changes in placental weight (p < 0.05) and fetal glucose levels (p < 0.02) were observed in the severely diabetic group. CONCLUSIONS: Placental glucose transporting and phosphorylating protein levels by themselves do not regulate diabetes-induced fetoplacental alterations. The lack of a protective decline in these proteins may account for the observed fetoplacental adaptations to excess glucose.

Delayed ultrastructural lung maturation in the fetal and newborn hypothyroid (Hyt/Hyt) mouse.

Thyroid hormones influence fetal and neonatal lung growth and maturation. However, the effect of naturally occurring, genetically determined hypo- or hyperthyroidism on fetal or neonatal lung maturation has not been examined. In the hyt/hyt mouse, primary hypothyroidism, which is characterized by a high serum TSH concentration, is transmitted as an autosomal recessive trait. It occurs due to a mutational defect in the beta-subunit of the TSH receptor. We studied the lung ultrastructure of the fetal [18-d-gestation (term = approximately 19.5 d)] and neonatal (< 1-d-old) hyt/hyt mouse. In addition, disaturated phosphatidylcholine and total phospholipid contents of newborn hyt/hyt mouse lungs were determined. Male and female hyt/hyt mice with a high serum TSH concentration were made euthyroid by adding 3,5,3'-triiodothyronine to drinking water and then mated. Balb-c mice served as euthyroid controls. Fetal and neonatal hyt/hyt mice had a higher serum TSH concentration than the Balb-c controls. Fetal hyt/hyt mouse lungs showed a large amount of intracellular glycogen and fewer lamellar bodies in epithelial type II cells compared with Balb-c fetal mouse lungs. The neonatal hyt/hyt mouse also showed signs of lung immaturity such as persistent epithelial cell glycogen, few lamellar bodies, reduced disaturated phosphatidylcholine content, and absent tubular myelin. We conclude that fetal and neonatal lung maturation is delayed in the hyt/hyt mouse with primary hypothyroidism.

Hyperoxia induces interstitial (type I) and increases type IV collagenase mRNA expression and increases type I and IV collagenolytic activity in newborn rat lung.

Oxygen toxicity is attributed to the reaction of oxygen metabolites with cellular components leading to cell destruction. Activation of latent human neutrophil interstitial collagenase by reactive oxygen species has been demonstrated. The potential role of collagenases in hyperoxic lung injury has not been investigated. We studied the effect of hyperoxia on newborn rat lung water content, morphology and ultrastructure, interstitial (type I) and type IV collagenase gene expression and type I and IV collagenolytic activity. We observed that hyperoxia causes pulmonary edema, alters newborn rat lung morphology in a sequential manner and produces ultrastructural alterations, induces type I and increases type IV collagenase mRNA expression, and increases type I and IV collagenolytic activity. A role for type I and IV collagenase in hyperoxic newborn lung injury or in the recovery following the injury is proposed.

Effect of maternal diabetes on the expression of genes regulating fetal brain glucose uptake.

Diabetes alters adult brain glucose uptake and glucose transporter 1 gene expression. To investigate the effect of diabetes on genes regulating fetal brain glucose uptake, we examined the effect of moderate (blood glucose 10-16.7 mM, normoinsulinemia) and severe (blood glucose > 16.8 mM, hypoinsulinemia) maternal diabetes on the expression of genes regulating fetal brain glucose uptake in the genetically nonobese diabetic mouse. In the moderately diabetic state, a 50% decline in fetal brain GLUT1 mRNA levels was associated with a 20% increase in the corresponding GLUT1 protein levels. Simultaneously, although fetal brain GLUT3 mRNA and protein levels were barely detectable, no change in hexokinase I enzyme mRNA, protein (115,000 and 100,000 M(r)) or activity, was noted. In the severe form of maternal diabetes GLUT1 protein was unchanged, GLUT3 protein levels remained low, and a 2- to 3-fold increase in the lower molecular form of the hexokinase I protein (100,000 M(r)) and enzyme activity occurred. These observations suggest that moderate and severe forms of maternal diabetes do not affect the fetal brain glucose transporter levels to a physiologically significant extent. The severe form of maternal diabetes, however, enhances 1.5- to 3-fold the expression and activity of hexokinase I. This enzyme mediates the rate-limiting step in brain glucose metabolism, namely the intracellular conversion of glucose to glucose-6-phosphate.

Effect of maternal administration of thyrotropin-releasing hormone or DN1417 on functional and morphologic fetal rabbit lung maturation and duration of survival after premature delivery.

Though maternal treatment with thyrotropin-releasing hormone (TRH) for prevention of hyaline membrane disease has been utilized, precise mechanisms of TRH in accelerating fetal lung maturation remain unclear. We studied the effect of maternally administered TRH or DN1417 (an analog of TRH) on functional and morphologic fetal rabbit lung maturation and the duration of survival after premature delivery. Because DN1417 retains the neurotransmitter but not the neuroendocrine effects of TRH, this study enables us to determine which of these effects was responsible for enhancement of lung maturation. TRH or DN1417 (0.2 mg/kg/dose) or saline was injected intravenously into New Zealand White rabbit does 48, 36, 24, 12 and 2 h prior to sacrifice on day 27 of gestation. Functional pulmonary maturity was assessed by pressure-volume hysteresis, and morphologic maturity was assessed by histologic technique. Maternal administration of TRH or DN1417 enhanced both functional and morphologic fetal lung maturation as well as the duration of neonatal survival after premature delivery. We propose that the effect of TRH in fetal lung maturation is due to neurotransmitter rather than neuroendocrine effects.

The fetal heart insulin receptor responds differently to varying plasma insulin concentrations.

We investigated in vivo the effect of varying plasma concentrations of insulin on the 28- and 30-day-old fetal rabbit heart insulin receptors using plasma membranes. Alloxan induced maternal diabetes (n = 5) associated with fetal hyperglycemia and mild hyperinsulinemia (59.80 +/- 8.10 microU/ml versus a control of 26.25 +/- 3.70, p less than 0.01) increased the insulin receptor number from a control (30 d) of 168 +/- 1.01 to 320 +/- 34 X 10(10)/mg protein (p less than 0.01). Fetal administration of 1.0 U of insulin (n = 4) resulting in normoglycemia and moderately high plasma insulin concentrations (103.3 +/- 34.63 microU/ml versus a control of 13.72 +/- 1.60, p less than 0.05) did not alter the insulin receptor number (28 d). On the other hand fetal administration of 2.0 U of insulin (n = 4) resulting in hypoglycemia and severely high plasma insulin concentrations (288.3 +/- 51 microU/ml versus a control of 13.72 +/- 1.60, p less than 0.01) decreased the insulin receptor number from a control (28 d) of 200 +/- 23 to 82 +/- 23 X 10(10)/mg protein (p less than 0.01). The receptor affinity remained constant. We conclude that the downregulation (decrease) of the fetal heart insulin receptors in vivo is not a physiologic but a pharmacologic effect of insulin.

Acute bronchospasm resembling status asthmaticus during the neonatal period.

Recently, we encountered four neonates who developed severe reversible partial lower airway obstruction. This communication describes their clinical course and the pathogenesis and treatment of acute bronchospasm resembling status asthmaticus and leading to life-threatening respiratory acidosis.

Varying brain insulin concentrations differentially regulate the fetal brain insulin receptor.

We investigated the downregulating effect of varying states (physiologic and pharmacologic) of systemic and intracranial hyperinsulinism on the 28 to 30 day fetal rabbit brain insulin receptor. Alloxan-induced maternal diabetes (n = 5) produced mild fetal hyperinsulinemia (D) (plasma insulin concentrations = 59.80 +/- 8.10 microU/ml, control = 26.25 +/- 3.70; p less than 0.01), whereas systemic administration (IMI) of 1.0 U (n = 4) and 2.0 U (n = 4) of insulin to the fetus resulted in moderate (103.13 +/- 34.63 microU/ml) and severe (288.3 +/- 51 microU/ml) fetal hyperinsulinemia respectively. All three states of systemic hyperinsulinemia neither altered the fetal brain insulin content nor the brain insulin receptor number and affinity. 0.01 U (n = 4) of intracranial insulin administration (ICI) increased the brain insulin content four-fold (p less than 0.01) but did not alter the brain insulin receptor number or affinity. 0.1 (n = 5) and 2.0 U (n = 7) of intracranial insulin increased the brain insulin content to supraphysiologic concentrations (p less than 0.01) and decreased the fetal brain insulin receptor number (p less than 0.01), the affinity remaining constant. We conclude that 1) regardless of the ability of insulin to cross the blood brain barrier, the downregulation of the brain insulin receptor is insulin dose-dependent and 2) the downregulation of the fetal brain insulin receptor is not a physiologic but a pharmacologic effect of insulin.

Altered thyroidal states modulate the insulin receptor characteristics of the developing rabbit brain.

We investigated the effect of propylthiouracil (PTU)-induced hypothyroidism and T4-induced hyperthyroidism on the fetal and neonatal rabbit brain insulin receptors (number and affinity) using plasma membranes. PTU administration to the pregnant mothers resulted in low serum-free T4 and normal total T3 concentrations, while T4 therapy to the mothers resulted in high serum-free T4 and high total T3 concentrations in the fetus and neonate. PTU-induced hypothyroidism did not affect the fetal brain insulin receptors, cholesterol content (brain homogenate) or protein content. On the other hand, brain insulin receptor number and total brain cholesterol content decreased in the neonate. T4 therapy at 100 micrograms/kg reversed the serum T4 to the control value and normalized the neonatal brain insulin receptor number and cholesterol content while a higher dose of T4 (200 micrograms/kg) increased the neonatal brain insulin receptor number, cholesterol and protein content. We conclude that altered thyroidal states modulate the brain insulin receptor (number and affinity) in neonatal, but not fetal brain plasma membranes.

Ontogenesis of the insulin receptor in the rabbit brain.

We delineated the ontogeny of the brain insulin binding, insulin receptor number and affinity using plasma membranes isolated from the rabbit. Specific 125I-insulin binding and receptor number expressed per milligram of protein increased from the 20 day gestation fetus to the 1-day-old newborn, declining thereafter to attain adult values by day 6 of postnatal life. Specific 125I-insulin binding and the receptor number in the adult brain was less than the fetal and neonatal (1 day) brain receptors. Although a similar trend was observed specifically during fetal development, the changes in receptor number expressed per microgram DNA were not significant in the neonatal period. The adult brain insulin receptor number was higher than the 20- to 27-day fetus and similar to that of the 30-day fetus and the 1- to 5-day newborns. The total receptor number correlated linearly with the brain plasma membrane protein increment velocity. The affinity of the receptors increased during early fetal development (20-27 days) and remained constant thereafter in the postnatal period. We conclude that the ontogenic changes of the brain insulin receptors are similar to the ontogenic changes of brain plasma membrane protein. The developmental changes are more pronounced when the receptor number is expressed per milligram protein versus microgram DNA.

Ontogeny of plasma-free thyroxine and triiodothyronine concentrations during the perinatal period and maternofetal transfer of thyroid hormones in the rabbit.

Although rabbit has been used as a convenient animal model in understanding the role of thyroid hormones during the perinatal development, ontogenetic changes in plasma-free thyroxine or triiodothyronine concentration has not been studied in this species. We delineated the ontogeny of immunoreactive plasma-free thyroxine and triiodothyronine concentration during the perinatal period. It is generally believed that thyroid hormones do not cross the placenta from the mother to the fetus in sufficient concentrations to exert biological effects in the fetus. We administered 250 micrograms/kg of thyroxine (T4) or 125 micrograms/kg of triiodothyronine (T3) intramuscularly to the rabbit doe on the 25th and 26th day of gestation. Maternal and fetal plasma-free T4, T3 and glucose concentration and fetal liver glycogen content were quantitated on the 27th day of gestation. Maternal and fetal plasma-free T4 and T3 concentration was significantly higher than the control in T4-treated animals. Maternal and fetal plasma T3 concentration was higher and free T4 concentration lower than the control in T3-treated animals. T3 or T4 treatment resulted in fetal hyperglycemia and depletion of fetal hepatic glycogen content. We conclude that T4 or T3 cross the rabbit placenta and exert thyromimetic effects in the fetus. A convenient animal model to investigate in utero effects of T4 or T3 in mammalian fetal development is proposed.

A differential effect of thyroxine and glucocorticoids on fetal brain and heart insulin receptor.

We investigated the effect of thyroxine (T4), glucocorticoids, and T4 + glucocorticoids on the maturation of fetal rabbit brain and heart insulin receptors. Five doses of T4 over 10 days (50 micrograms/kg body weight per dose) were administered to the mother; significant amounts crossed the placenta (fetal serum free T4 = 0.75 +/- 0.08 versus a control of 0.21 +/- 0.02 ng/dl, p less than 0.02) and increased the specific binding of [125I]insulin to 30-day-old fetal heart membranes from a control of 3.6 +/- 0.74% per 100 micrograms protein to 5.8 +/- 0.19% (p less than 0.05). Curvilinear Scatchard plots revealed an increase in receptor number X 10(7) micrograms protein-1 from 137 +/- 4 to 244 +/- 39 (p less than 0.05) with no change in receptor affinity. No appreciable alteration by T4 in the [125I]insulin-specific binding and receptor number of 30-day fetal brains was noted. Fetal heart glycogen content was decreased and there was a small increase in plasma glucose concentration in the T4-treated group (each p less than 0.02). Betamethasone at 0.17 mg/kg did not affect the specific binding of [125I]insulin to 27-day fetal heart or brain plasma membranes, although a decrease in heart glycogen content and an increase in plasma glucose concentration were observed (each p less than 0.02). Also T4 + betamethasone did not alter the [125I]insulin binding to 27-day fetal heart or brain plasma membranes, but resulted in an additive effect (a marked depletion) on cardiac glycogen (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid-dependent maturation of neonatal brain but not lung epidermal growth factor receptors.

Although the role of thyroid hormones in enhancing lung and brain maturation during the perinatal period is well established, the cellular mechanisms involved in these processes are incompletely understood. Hypothyroidism retards the development of fetal pulmonary insulin, neonatal pulmonary beta-adrenergic and neonatal brain insulin receptors. In this study, we investigated the effect of hypo- or hyperthyroidism on the development of neonatal brain and lung epidermal growth factor (EGF) receptors. The rabbit pups were rendered hypothyroid by adding 0.05% propylthiouracil to the drinking water starting at 23 days of gestation and thereafter. The neonatal hyperthyroid state was achieved by intramuscular administration of 100 micrograms/kg of synthroid to the rabbit doe on the 29th and 30th day of pregnancy. Neonatal plasma free thyroxine (T4) concentrations were quantitated by a radioimmunoassay. Brain and lung plasma membranes were isolated by differential centrifugation. EGF receptor characteristics were studied using 125I-EGF binding assays and Scatchard analysis. The plasma free T4 concentrations were 0.36 +/- (SEM) 0.02 (n = 6), p less than 0.01 (n = 7) and 1.76 +/- 0.1 (n = 6) ng/dl in the control, hypothyroid and hyperthyroid pups, respectively. The percent specific binding of 125I-EGF to 200 micrograms of brain plasma membrane (BPM) protein was significantly lower in the hypothyroid (0.62 +/- 0.03, n = 7, p less than 0.01), and higher in the thyroxine-treated (1.58 +/- 0.08, n = 6, p less than 0.01) group when compared to control (1.08 +/- 0.06, n = 6) animals. However, the percent specific binding of 125I-EGF to 100 micrograms of lung plasma membrane (LPM) protein was similar in all three groups (2.24 +/- 0.28, control; 2.01 +/- 0.5, hypothyroid, and 2.26 +/- 0.3, hyperthyroid). The number of EGF receptors per milligram of BPM protein (X 10(-10] were lower in the hypothyroid (2.24 +/- 0.03, n = 5) and higher in the hyperthyroid (6.6 +/- 0.02, n = 4) group when compared to control (4.4 +/- 0.05, n = 4) with no apparent difference in Kd. There was no difference in the number of EGF binding sites per milligram of LPM protein (X 10(-10] within the groups (6.6 +/- 0.8, n = 6, control; 7.9 +/- 0.4, n = 4, hypothyroid, and 7.3 +/- 0.3, n = 4, hyperthyroid). Presence of high affinity receptors for EGF in the neonatal brain as well as lung supports the hypothesis that EGF may play an important role in neonatal brain and lung maturation.(ABSTRACT TRUNCATED AT 400 WORDS)