Thyroid Function in Fetal Sheep1

Barnes, Charles M.; Warner, Darren; Marks, S.; Bustad, L.K.

doi:10.1210/endo-60-2-325

Cited by 28 publications

(12 citation statements)

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“…1 and 2 would indicate that the specific function of the thyroid gland, as measured by 1131 uptake, did not suddenly and precipitously develop within 24 hours but had been present in some glands for one or more days prior to day 19. The exponential development described here for the rat has also been reported previously by Hall and Kaan (5), and for human, bovine, and sheep fetal thyroids by others (15)(16)(17).…”

Section: Discussionsupporting

confidence: 85%

Maturation of the Rat Fetal Thyroid

Feldman

Vazquez

Kurtz

1961

The Journal of Cell Biology

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Maturation of the rat fetal thyroid was studied with the aid of 1131 and of fluorescence and electron microscopy. The I ~31 concentration of the fetal gland increased exponentially from day 17 to day 20 of gestation and was related to the weight of the fetus (and presumably the weight of the thyroid) and also to the quantity of 113t accumulated by the fetus. In the 17-day gland, thyroglobulin or immunologically similar material was sparsely present in the incipient lumens of some cell clusters. With maturation, this material increased and was also observed within follicular cells on days 18 to 19 of gestation. On day 20, the specifically reacting material was present in the follicular lumens and was absent from the cytoplasm of follicular epithelium. Ultrastructurally, the earliest thyroid cells examined were replete with all the organelles found in the more mature epithelium. No direct correlation could be made between the cytoplasmic structures and the presence of thyroglobulin, although the granular endoplasmic reticulum was most likely the organelle responsible for synthesis of thyroglobulin. Thyroglobulin or a precursor was found in fetal thyroid cells before measurable quantities of 113~ were concentrated and before cytoplasmic droplets appeared.Between day 18 and day 19 of gestation, the fetal thyroid of the rat acquires the capacity to concentrate easily measurable quantities of I t3t (1). Based on this property of isotope accumulation by the fetal thyroid, and with the aid of electron and fluorescence microscopy, the following study was designed to seek answers to three questions: First, does an intracellular organelle appear or become singularly prominent at the time the thyroid gland begins to trap iodide in high concentration? Second, during the maturation of the fetal thyroid, is it possible to localize the site of synthesis of specific thyroid protein, thyroglobulin? Third, is thyroglobulin or a precursor produced before the advent of iodide concentration by the gland? MATERIALS AND METHODSPregnant rats (Holtzman) with known mating times were injected subcutaneously on the 16th to 19th day of gestation a with 50 to 60 #c of 1131. 24 hours later the fetuses were removed from their etherized dams and their thyroids were visualized under a stereomicroscope. The glands to be processed for electron microscopy were flooded with 2 per cent osmium tetroxide in situ as quickly as possible after removal of the fetus from the uterus, usually within less than 1 minute. After freeing from the trachea, they were placed in 1 per cent buffered osmium tetroxide containing sucrose for 1 to 2 hours and then processed for Vestopal W embedding. Other fetal glands were embedded in a small piece of maternal 1 24 hours after a vaginal smear positive for sperm was counted as 1 day of gestation.

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Section: Discussionsupporting

confidence: 85%

Maturation of the Rat Fetal Thyroid

Feldman

Vazquez

Kurtz

1961

The Journal of Cell Biology

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“…At about 50 days of gestation, radioiodine uptake in thyroid follicles in the fetal sheep has been observed [Barnes et a!., 1957] and T4 and TSH have been de tected in the fetal plasma [Thorbum and Hopkins, 1973], although the origin of the T4 is uncertain [Potter et al, 1980b], The present observation of small numbers of mildly affected thyroidectomy cells in fetal sheep pituitary glands at 58 days of gesta tion indicates that the pituitary thyrotrophs are able to respond to lowered plasma thy roid hormone concentrations at this age and that a major component of the feed back mechanism exists before 60 days of gestation.…”

Section: Discussionmentioning

confidence: 99%

“…The organization of cells into follicles and the accumulation of iodine by the fetal sheep thyroid have been observed from about 50 days of gestation [Barnes et al, 1957] and thyrotrophs have been described in electron microscopic studies of fetal sheep pituitaries at 54 days [Alexander el al., 1973] and 64 days [Webb, 1981]. In addition, thy roxine (T4) and thyroid-stimulating hormo ne (TSH) have been detected in the fetal plasma from as early as about 50 days [Thorburn and Hopkins, 1973].…”

Section: Introductionmentioning

confidence: 99%

Ultrastructural Detection of the Onset of Pituitary Thyrotroph Sensitivity to Lowered Thyroid Hormone Concentrations in the Fetal Sheep

Perry

McIntosh

Robinson

1983

Cells Tissues Organs

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The goitrogen methylthiouracil was administered orally to pregnant ewes of known gestational ages to induce hypothyroidism in both mother and fetus. Developing pituitary thyrotrophic cells were studied using electron microscopy to detect the earliest gestational age at which morphological changes occurred in response to lowered plasma thyroid hormone concentrations. At 50 days of gestation, the pituitaries of fetuses exposed to the goitrogen were indistinguishable from untreated control glands. However, at 58 days and subsequent ages, ‘thyroidectomy’ cells were observed in pituitaries of all hypothyroid fetuses. These findings indicate that fetal sheep pituitary thyrotrophs are sensitive to lowered thyroid hormone concentrations by 58 days of gestation, suggesting that thyroid-thyrotroph interaction exists at this early stage of development.

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“…In the ovine fetus, fetal thyroid function begins at the start of the second trimester (4). The ovine placenta is relatively impermeable to both T4 and triiodothyronine (T3), whether the fetus is euthyroid or athyrotic (10,11).…”

Section: Discussionmentioning

confidence: 99%

Pulmonary Superoxide Dismutase Activity in the Euthyroid and Hypothyroid Ovine Fetus

et al. 1982

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SummaryPulmonary superoxide dismutase (SOD) activity was measured in 11 euthyroid and 15 hypothyroid ovine fetuses at 130 days gestation. In the euthyroid fetus, the mean pulmonary SOD activity was similar in saline-and thyroxine-infused groups. Compared to the euthyroid fetus, the mean pulmonary SOD activity was significantly lower in the noninfused or saline-infused athyrotic fetus. Administration of thyroxine to the hypothyroid fetus results in a normalization of pulmonary SOD activity to control values. Thug, thyroxine appears to influence the maturation of pulmonary SOD activity in the ovine fetus during the third trimester. SpeculationThe influence of thyroxine on pulmonary SOD activity was studied in the euthyroid and hypothyroid sheep fetus during the last trimester of gestation.Superoxide dismutase (SOD), an enzyme which catalyzes the reaction: 2 O2 + 2 H+ + HzOz + 02, is found in all cells that metabolize oxygen (9,14). Despite numerous studies investigating the role of SOD activity in oxygen-induced lung injury, there is little information regarding the mechanisms responsible for endogenous regulation of pulmonary SOD activity (14). It is known that pulmonary SOD activity is lowest in the fetus, with an increase in activity seen in the neonatal and adult lung (2,23,26). In contrast to the adult lung, the neonatal lung exposed to a hyperoxic environment will increase pulmonary SOD activity, a response mediated at least in part by a factor(s) in plasma or serum and exposure to oxygen (2,13,21,24).It has been shown previously that pulmonary oxygen toxicity can be influenced by thyroid function. In the adult, pulmonary oxygen toxicity is enhanced by hyperthyroidism and delayed by hypothyroidism (6,20,25). Iodothyronines have also been shown to influence the maturation of the fetal lung (12,17,22). If thyroid hormones are used to pharmacologically accelerate fetal lung maturation, the fetus would be, in theory, at greater risk for the development of pulmonary oxygen toxicity. The purpose of this study was to investigate the relationship of iodothyronines and pulmonary SOD activity in the preterm ovine fetus. MATERIALS AND METHODSAnimal model. Date bred ewes were obtained from a local source, maintained at the University of Iowa vivarium and given free access to alfalfa and water. In fifteen singleton ewes, a surgical thyroidectomy was performed on the fetus at 95-99 days gestation. Term is 147 to 150 days. In nine of the hypothyroid fetuses, catheters were inserted into a fetal artery and vein at 122-124 days gestation. After a 3-5 day stabilization period, five fetuses received a 50 pg bolus intravenous injection of thyroxine (T4) followed by a continuous intravenous infusion of 100 &day of T4 for 72 h before sacrifice. Four fetuses received a constant infusion of an equivalent volume of saline. These nine fetuses and six noninfused fetuses were sacrificed at 130 days gestation.Eleven euthyroid ovine fetuses had catheters inserted into a fetal artery and vein at 122-124 days gestation. After a three-five ...

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Thyroid Function in Fetal Sheep1

Cited by 28 publications

References 0 publications

Maturation of the Rat Fetal Thyroid

Maturation of the Rat Fetal Thyroid

Ultrastructural Detection of the Onset of Pituitary Thyrotroph Sensitivity to Lowered Thyroid Hormone Concentrations in the Fetal Sheep

Pulmonary Superoxide Dismutase Activity in the Euthyroid and Hypothyroid Ovine Fetus

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