Thyroid hormones are important for normal bone growth and development in postnatal life. However, little is known about the role of thyroid hormones in the control of bone development in the fetus. Using computed tomography and mechanical testing, the structure and strength of metatarsal bones were measured in sheep fetuses in which thyroid hormone levels were altered by thyroidectomy or adrenalectomy. In intact fetuses, plasma concentrations of total calcium and the degradation products of C-terminal telopeptides of type I collagen increased between 100 and 144 days of gestation (term 145±2 days), in association with various indices of bone growth and development. Thyroid hormone deficiency induced by thyroidectomy at 105–110 days of gestation caused growth retardation of the fetus and significant changes in metatarsal bone structure and strength when analyzed at both 130 and 144 days of gestation. In hypothyroid fetuses, trabecular bone was stronger with thicker, more closely spaced trabeculae, despite lower bone mineral density. Plasma osteocalcin was reduced by fetal thyroidectomy. Removal of the fetal adrenal gland at 115–120 days of gestation, and prevention of the prepartum rises in cortisol and triiodothyronine, had no effect on bodyweight, limb lengths, metatarsal bone structure or strength, or circulating markers of bone metabolism in the fetuses studied near term. This study demonstrates that hypothyroidism in utero has significant effects on the structure and strength of bone, with different consequences for cortical and trabecular bone.
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- Abstract: Thyroid* x
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S A Lanham, A L Fowden, C Roberts, C Cooper, R O C Oreffo and A J Forhead
(1) The interaction between thyroid hormone and thyroxine-binding globulin (TBG) has been studied in 39 pigs from eight litters, aged from 12 hr. to 11 days. In addition, single observations were made on six batches of 42 pigs from 1 day to 6 months old and in five newborn sheep.
(2) A rapid increase in the level of the unsaturated TBG capacity was found to occur from the 1st day after birth.
(3) Continuous changes in the unsaturated TBG capacity resulted in a decline in the plasma level of free thyroxine and in a decrease in the uptake of [131I]triiodothyronine by erythrocytes. Equilibrium between the hormonal iodine metabolism and its blood carrier is reached at the end of the 1st week of life.
(4) These findings suggest that in discussing thyroid metabolism in neonatal animals it is important to distinguish between the early neonatal adaptive period and the remainder of the period of thyroid hyperactivity. The physiological implications of the higher level of free thyroxine in the blood after birth for the adaptation to post-uterine life is discussed.
SM van der Heide, TJ Visser, ME Everts and PH Klaren
We have investigated the potential role of fibroblasts in local thyroid hormone metabolism in neonatal rat heart. Incubation of cardiac fibroblasts with thyroxine (T4) or 3,5,3'-tri-iodothyronine (T3) resulted in the appearance of water-soluble metabolites, whereas incubation of cardiomyocytes under the same conditions did not or did so to a much lesser extent. Time-course studies showed that production is already evident after 1-5 h of exposure and that the process equilibrates after 24-48 h. Analysis of the products revealed both the T4 and the T3 metabolites to be glucuronides. These results were corroborated by the detection of uridine diphosphate (UDP)-glucuronyltransferase activity in cardiac fibroblasts. We found no indication for outer ring deiodination in fibroblasts, cardiomyocytes or heart homogenates. From these results we have concluded that cardiac fibroblasts, but not cardiomyocytes, are able to glucuronidate T4 and T3 and secrete the conjugates. This could play a role in local metabolism, e.g. to protect the heart tissue from high levels of thyroid hormones.
J Patel, K Landers, H Li, R H Mortimer and K Richard
The development of fetal thyroid function is dependent on the embryogenesis, differentiation, and maturation of the thyroid gland. This is coupled with evolution of the hypothalamic–pituitary–thyroid axis and thyroid hormone metabolism, resulting in the regulation of thyroid hormone action, production, and secretion. Throughout gestation there is a steady supply of maternal thyroxine (T4) which has been observed in embryonic circulation as early as 4 weeks post-implantation. This is essential for normal early fetal neurogenesis. Triiodothyronine concentrations remain very low during gestation due to metabolism via placental and fetal deiodinase type 3. T4 concentrations are highly regulated to maintain low concentrations, essential for protecting the fetus and reaching key neurological sites such as the cerebral cortex at specific developmental stages. There are many known cell membrane thyroid hormone transporters in fetal brain that play an essential role in regulating thyroid hormone concentrations in key structures. They also provide the route for intracellular thyroid hormone interaction with associated thyroid hormone receptors, which activate their action. There is a growing body of experimental evidence from rats and humans to suggest that even mild maternal hypothyroxinemia may lead to abnormalities in fetal neurological development. Our review will focus on the ontogeny of thyroid hormone in fetal development, with a focus on cell membrane transporters and TR action in the brain.
Anita Boelen, Anne H van der Spek, Flavia Bloise, Emmely M de Vries, Olga V Surovtseva, Mieke van Beeren, Mariette T Ackermans, Joan Kwakkel and Eric Fliers
Illness induces major modifications in central and peripheral thyroid hormone (TH) metabolism, so-called nonthyroidal illness syndrome (NTIS). As a result, organ-specific changes in local TH availability occur depending on the type and severity of illness. Local TH availability is of importance for the regulation of the tissue-specific TH target genes and determined by the interplay between deiodinating enzymes, TH transport and TH receptor (TR) expression. In the present study, we evaluated changes in TH transport, deiodination and TR expression, the resulting tissue TH concentrations and the expression of TH target genes in liver and muscle in three animal models of illness. We induced (1) acute systemic inflammation by intraperitoneal injection of bacterial endotoxin (LPS), (2) chronic local inflammation by a turpentine injection in the hind limb and (3) severe pneumonia and sepsis by intranasal inoculation with Streptococcus pneumoniae. We found that all aspects of peripheral TH metabolism are differentially regulated during illness, depending on the organ studied and severity of illness. In addition, tissue TH concentrations are not equally affected by the decrease in serum TH concentrations. For example, the decrease in muscle TH concentrations is less severe than the decrease observed in liver. In addition, despite lower TH concentrations in muscle in all three models, muscle T3 action is differentially affected. These observations help to understand the complex nature of the nonthyroidal illness syndrome.
W. C. ADAMS and J. H. LEATHEM
Immature female rats were fed thiouracil for 30 days and injected with 10 i.u. human chorionic gonadotrophin (HCG) for the last 20 days. In thiouracil-fed animals, HCG produced large ovaries containing follicular cysts. These ovaries showed a subnormal concentration of cholesterol but both a normal total content and normal incorporation of [1-14C]acetate into digitonin-precipitable-sterols. Liver and serum cholesterol concentrations were reduced, but in vivo, 4 hr. incorporation of acetate into sterols was doubled suggesting either an acceleration of cholesterol turnover or delayed utilization of sterol precursors of cholesterol. HCG also reduced ovarian cholesterol concentration in euthyroid animals but total organ content and incorporation of [14C]acetate were not altered, nor were liver and serum cholesterol affected. Since the effect of induced ovarian cysts on sterol metabolism cannot be accounted for by known effects of thyroid or gonadal hormones it is suggested that influences of steroid hormones on lipid metabolism may be greatly modified in thyroid deficiency.
L. F. B. P. Costa Rosa, Y. Cury and R. Curi
In the present study the effects of insulin, glucocorticoids and thyroid hormones on macrophage metabolism and function were investigated. The maximum activities of hexokinase, glucose-6-phosphate dehydrogenase, glutaminase and citrate synthase were determined in macrophages obtained from hormonetreated rats and those cultured for a period of 48 h in the presence of hormones. Macrophage phagocytosis was markedly inhibited by dexamethasone and thyroid hormones, remaining unchanged when insulin was added to the culture medium, however. The changes in the enzyme activities caused by hormone treatments of the rats were very similar to those found in culture. Insulin enhanced citrate synthase and hexokinase activities and diminished those of glutaminase and glucose-6-phosphate dehydrogenase. Dexamethasone had a similar effect except on glucose6-phosphate dehydrogenase. The addition of thyroid hormones to the culture medium raised the activities of glutaminase and hexokinase and reduced that of citrate synthase. The results presented support the suggestion that the effects of insulin, glucocorticoids and thyroid hormones on immune and inflammatory responses could well be mediated through changes in macrophage metabolism..
Journal of Endocrinology (1992) 135, 213–219
G. C. LIGGINS and P. C. KENNEDY
Electrocoagulation lesions involving 70–100% of the hypophysis of 17 foetal lambs were made at various times between 93 and 136 days of gestation. Foetal growth and development after the operation was compared with that in a group of seven control lambs comprising three intact littermates of operated foetuses and four sham-operated foetuses. Hypophysial damage was found to be associated with retardation of somatic development which was most marked when the operation was performed early in gestation. Retardation was particularly evident in epiphysial development. Hypoplasia of the adrenal cortices, the interstitial cells of the testis and the thyroid glands confirmed the assumption made by previous workers based on decapitation experiments, that the foetal hypophysis exerts a trophic influence on the development of these endocrine organs. Reduced liver glycogen content and plasma glucose levels indicated a disturbed carbohydrate metabolism. Abnormal subcutaneous fat deposition suggested disorders in fat metabolism. Delayed involution of haemopoietic tissues, hypoplasia of peripheral lymphoid tissue and reduction in the number of mast cells in the skin were also noted. Structures of ectodermal origin were relatively unaffected by hypophysial lesions. It is concluded that the hypophysis of the foetal lamb subserves many of the functions attributed to it during extrauterine life.
R. E. KRAMER and H. D. COLBY
Department of Physiology and Biophysics, West Virginia University School of Medicine, Morgantown, West Virginia 26506, U.S.A.
(Received 25 June 1976)
Many studies have established the importance of the gonadal hormones in the regulation of hepatic steroid and drug metabolism in rats (Yates, Herbst & Urquhart, 1958; Kitay, 1963; Conney, 1967; Gillette, Davies & Sasame, 1972). The activity of hepatic steroid Δ4-hydrogenase, the rate-limiting step in corticosteroid metabolism, is enhanced by oestradiol and diminished by testosterone administration. Consequently livers from female rats metabolize corticosteroids more rapidly than those from male rats. In contrast the metabolism of many drug substrates by hepatic microsomal cytochrome P-450-containing enzymes is increased by testosterone (Quinn, Axelrod & Brodie, 1958) and inhibited by oestradiol (Murphy & DuBois, 1958), resulting in a sex difference in oxidative drug metabolism opposite to that in reductive (Δ4-hydrogenase) steroid metabolism. We recently reported that the effects of gonadal hormone on both hepatic
B. F. CLARK
Department of Hormone Physiology, Imperial Cancer Research Fund, Lincoln's Inn Fields, London, WC2A 3PX
(Received 19 February 1975)
Oestrogen treatment in vivo increases the metabolism of progesterone by the rat uterus in vitro (Armstrong & King, 1971; Howard & Wiest, 1972). However, the pattern of metabolites produced is dependent on the concentration of progesterone used in vitro (Saffron, Loeser, Haas & Stavely, 1974). When high concentrations of progesterone were used, oestrogen increased both ring A and C20-ketone metabolism. At low concentrations oestrogen increased C20-ketone metabolism, whereas ring A metabolism was decreased.
This present experiment was carried out to see whether oestrogen affected uterine metabolism of progesterone in vivo in mice (Clark, 1973, 1974) in the same way.
[1,2,6,7-3H] Progesterone (5 or 500 pg; sp. act. 261 μCi/μg, Radiochemical Centie, Amersham) was injected intraluminally into both uterine horns of spayed mice 1 or 6 days after oestrogen priming as described by