Daily Injections Of Thyroxine Research Articles

Long Days and Thyroxine Program American Tree Sparrows for Seasonality: Evidence for Temporal Flexibility of the Breeding Season of Euthyroid Females

To explore the role of the thyroid in the control of seasonality, photosensitive female American tree sparrows (Spizella arborea) were thyroidectomized (THX), moved to long days, and given daily injections of thyroxine (T4) for 3 weeks; THX and thyroid-intact (THI) controls received daily injections of alkaline vehicle. Birds were retained on long days 4 additional weeks and then moved to constant light and given T4in drinking water for 5 weeks in order to test for photorefractoriness. Endpoints were ovarian mass, molt score, and hypothalamic cGnRH-I (chicken gonadotropin-releasing hormone I) content; data were collected as independent measures at intervals of 1 to 5 weeks. THX females given T4replacement therapy (THXT4females) exhibited all components of seasonality (i.e., photoperiodic ovarian growth, photorefractoriness, and postnuptial molt), as did THI females. THX females not given replacement T4were aseasonal: They showed only minor thyroid-independent photoperiodic ovarian growth; they remained photosensitive, despite chronic photostimulation; and they did not initiate postnuptial molt. Collectively, these observations support, and extend to female tree sparrows, our model of seasonality in male tree sparrows, wherein control circuits are programmed for gonadal growth, photorefractoriness, and postnuptial molt by interactive effects of long days and thyroid hormone during the first 3 weeks of photostimulation. The unexpected finding that constant light and/or exogenous T4extended the simulated breeding seasons of some THI females prompted us to investigate the nature and expression of photorefractoriness. Our approach was to evaluate the same endpoints as before in chronically photostimulated THI females either retained on long days, with or without T4in drinking water, or moved to constant light, with or without T4. The results showed that exposure to constant light (not T4) near the end of a simulated breeding season can—though usually it does not—temporarily extend the breeding season and prevent the onset of postnuptial molt. It remains unclear whether these perturbations caused by constant light reflect a transitional relative photorefractoriness or merely a delay in the onset of absolute photorefractoriness. In either case, the thyroid- and daylength-dependent programs controlling seasonality in female American tree sparrows have a heretofore undemonstrated potential for limited temporal flexibility.

Coronary neovascularization of embryonic rat hearts cultured in oculo is independent of thyroid hormones

We tested the hypothesis that neovascularization of embryonic hearts is independent of thyroid hormones. To dissociate the effects of hemodynamic load from the direct influence of thyroid hormones on coronary neovascularization, we grafted avascular, gestational day 12 rat hearts to the anterior eye chamber of adult rats receiving daily injections of thyroxine (T4; 0.25 mg/kg sc), propylthiouracil (PTU; 10 mg/kg ip), or saline (control). After 21 days, grafts were perfuse fixed and prepared for transmission electron microscopy. Neither T4 nor PTU treatment affected size or mass of the unloaded graft, or the volume densities of vessels, myocytes, or the extracellular matrix, which were determined by standard point-counting techniques. Thus neither exogenous administration of T4 nor the induction of hypothyroidism in host rats produced a significant effect on the growth or vascularity of the unloaded hearts. We conclude that vascular growth in embryonic rat hearts cultured in oculo is independent of thyroid hormones and that the angiogenic effect of thyroid hormones in loaded hearts is a consequence of increased work-related events.

Increase in c- erbAα2 mRNA in the parvocellular region of the paraventricular nucleus of the hypothalamus following thyroidectomy in the adult male rat

To examine thyroid hormone regulation of c- erbAα2 mRNA expression in the parvo-cellular region of the paraventricular nucleus of the rat hypothalamus (pPVN), quantitative in situ hybridization was performed using 3H-labeled probe complementary to c- erbAα2 mRNA. Thyroidectomy induced a significant increase in the number of silver grains overlying the cytoplasm in the pPVN relative to sham-operated controls. This effect was prevented by daily injection of thyroxine. These results indicate that hypothyroidism induced an increase in cellular c- erbAα2 mRNA level in the pPVN.

In Vivo Regulation of Hepatic Insulin-Like Growth Factor-1 Messenger Ribonucleic Acids with Thyroid Hormone.

Insulin-like growth factor-1 (IGF-1) is synthesized primarily by the liver in response to growth hormone (GH). Thyroid hormone plays a major role in mediating pituitary GH secretion. In order to clarify the effect of thyroid hormone on IGF-1 gene expression, we measured hepatic IGF-1 mRNA levels in rats with thyroid dysfunction. Female Wistar rats were rendered hypothyroid by surgical thyroidectomy or hyperthyroid by daily injections of thyroxine (12 micrograms/day) for 2 weeks. Northern gel analysis of hepatic poly (A) RNA revealed the multiple sizes of the RNA transcripts ranging from 1.6 to 9.0 kb. After 4 weeks, hepatic IGF-1 mRNA levels were suppressed in hypothyroid rats, to less than 20% of control euthyroid animals. These suppressed mRNA levels were restored to euthyroid levels by thyroid hormone replacement for 2 weeks. Hyperthyroid rats, however, did not contain altered levels of hepatic IGF-1 mRNA as compared to euthyroid rats. The gamma-actin mRNA hybridization signal was not altered in hypothyroid or hyperthyroid rats. These results suggest that thyroid hormone regulates the in vivo expression of hepatic IGF-1 mRNA, probably through the mechanism of GH regulation.

Thyroxine effect on exocrine pancreatic development in rats.

Thyroxine and glucocorticoids both play important roles in regulating the development of mammalian tissues. The mechanisms by which they modulate the developmental process is not fully understood. Furthermore, the interaction between the effects of two hormones on the pancreas has not been studied in detail. To investigate these issues, we studied the effect of thyroxine and/or corticosterone on the development of the exocrine pancreas in normal and adrenalectomized rats. Daily injection of thyroxine (0.1 micrograms/g body wt) to pups starting at day 5 of age resulted in precocious increases of exocrine enzymes in the pancreata of these pups. Hypothyroid pups, induced by propylthiouracil, exhibited suppression of development of their pancreatic exocrine enzymes. Replacement of thyroxine or corticosterone alleviated the suppression of exocrine enzyme development in these pups. Rat pups, who underwent adrenalectomy at 5 days of age, had undetectable plasma corticosterone and exhibited similar suppression of pancreatic enzyme development. Injection of thyroxine or corticosterone alone to adrenalectomized pups led to normal development of exocrine pancreatic enzymes. When both thyroxine and corticosterone were given together to adrenalectomized pups, their pancreatic enzyme levels were found to increase to values above those of pups treated with thyroxine or corticosterone alone. We conclude that thyroxine has both direct and indirect modulatory roles in the development of the rat exocrine pancreas. Normal development of the exocrine pancreas depends on both intact adrenal and thyroid function in the rat.

Loss of sense of smell in adult, hypothyroid mice

Adult hypothyroid humans can lose their sense of smell. The present study was designed to investigate whether anosmia follows hypothyroidism in mice. If so, this would provide an animal model in which to study the mechanism for this effect. Adult mice were made hypothyroid with propylthiouracil (PTU) in their drinking water. Their sense of smell was tested before and after treatment by measuring the amount of time they spent sniffing food vs water odours, after a 24-h fast. Thyroid function was assessed histologically or by radioimmunoassay of blood serum for free thyroxine or free triiodothyronine. In Expt. I mice treated for 50 days with PTU were hypothyroid and anosmie. Control, euthyroid mice maintained their sense of smell, as did PTU-treated mice which also received daily thyroxine injections. PTU-induced anosmia was reversible: 50 days after removal of treatment previously anosmic mice were euthyroid and had regained their sense of smell (Expt. 3). It was possible that hypothyroidism induced non-specific effects which indirectly affected the olfactory function tests. However, short-term treatment with PTU caused severe hypothyroidism but no anosmia (Expt. 2). Additionally, non-specific effects of hypothyroidism were examined in open-field activity tests after short- and long-term hypothyroidism: euthyroid and hypothyroid animals were similarly active (Expts. 1 and 2). We conclude that chronic hypothyroidism produces anosmia in mice, as it does in humans. This anosmia is prevented by daily injections of thyroxine, and the sense of smell can recover to normal once thyroid function is restored.

Role of thyroxine in functional gastric development.

The role of thyroxine (T4) on the functional development of chief and parietal cells was studied in the rat. Daily injection of thyroxine (0.1 microgram/g body wt) resulted in the precocious appearance of pepsinogen in the oxyntic gland mucosa and an increase in basal acid output. Thyroxine had no effect in adrenalectomized rats. In propylthiouracil-induced hypothyroid pups, pepsinogen content and basal acid secretion were low. Corticosterone acetate (200 micrograms/g body wt) injection increased pepsinogen content and basal acid secretion in the absence of normal levels of thyroid hormones. We conclude that the effect of thyroxine on the development of chief and parietal cells is primarily due to accompanying changes in serum corticosterone.

Thyroxine-induced changes in the glycosylation pattern and in brain and serum levels of rat α-fetoprotein

1. 1. We have studied the effect of thyroid disfunction during the postnatal period, on the serum and brain levels of rat α-fetoprotein (AFP) and albumin. 2. 2. Hypothyroidism was induced by treatment of pregnant rats and their newborn pups with 2-mercapto-1-methylimidazole(methimazole). Hyperthyroidism was provoked in newborns by daily injections ofthyroxine (0.25 μg/g body wt) from the 3rd postnatal day to weaning. Impaired growth, lower brain size, altered behaviour and morphological features observed were according to an altered thyroid status. 3. 3. Hypothyroid rats showed a significantly reduction in serum AFP concentration (78% of control values at 8 days of age) and a slight increase in that of albumin. 4. 4. No significant changes were found in their brain AFP levels, while a somewhat higher brain albumin level could be appreciated. Thyroxine supplementation (0.2μg/rat/day) corrected most of these alterations. 5. 5. Hyperthyroidism induced a drastic fall in both serum and brain AFP levels (about 48% of the corresponding control values). 6. 6. Albumin concentration in serum was augmented significantly from the 12th postnatal day, but its brain levels did not change significantly. 7. 7. In hyperthyroid rats, a significant reduction (37% relative to controls) in the concanavalin A-non reactive microform of AFP, was observed. 8. 8. This alteration of the glycosylation pattern of AFP could be due to the inhibition by thyroxine of the activity of the hepatic enzyme GlcNAc-transferase III.

Prenatal and postnatal hypothyroidism abolishes lesion-induced noradrenergic sprouting in the adult rat.

The effects of altered thyroid states on regeneration in the central nervous system are equivocal. This work was undertaken to examine the influence of propylthiouracil-induced (PTU-induced) pre- and postnatal hypothyroidism on collateral sprouting of noradrenergic (NA) axons in the habenula (Hb), following lesions in the stria medullaris (SM) of the adult rat. Ten pregnant dams were divided into control and PTU-treated groups. Control rats had free access to food and water and the hypothyroid group received, in addition, 0.05% (w/v) of PTU in their drinking water, beginning on day 12 of gestation and continuing post partum through lactation until the offspring were weaned at age 22 days. The pregnant dams received, in addition, daily injections of thyroxine (25 micrograms/kg, ip) and only male pups were used in the study. At weaning the pups were removed from the dams and placed in cages with free access to food and water. The hypothyroid offspring received 0.05% (w/v) PTU in the drinking water until sacrificed at 10 weeks of age. At 6 weeks, some rats in each group received bilateral lesions in the SM and the remainder were sham-operated. All rats were sacrificed 4 weeks after operation. Thus, four groups were formed: 1) control/sham, 2) control/lesion, 3) PTU/sham, 4) PTU/lesion. Sprouting of NA fibers in discrete regions of the Hb was identified by norepinephrine (NE) levels and by fluorescence histochemistry. Blood levels of thyroid stimulating hormone (TSH) were determined. The results show that pre- and postnatal induced chronic hypothyroidism abolished NA sprouting in the partially deafferented Hb. Furthermore, lesions of the SM resulted in a marked decrease in serum TSH levels.

Delayed development of GFA immunoreactivity in intraocular cortex cerebri grafts during thyroid hormone deficiency

Dependency of astrocytes on thyroid hormones during development was studied in intraocular cortex cerebri grafts, using antibodies to the glial fibrillary acidic protein (GFA). Fetal cortex cerebri was left in the anterior eye chamber of normal and thyroidectomized adult recipient rats 3 and 8 weeks to mature. All cortex grafts survived and became vascularized in the eye. The grafts were cryostat-sectioned, and reacted with an antiserum specific for GFA. The density of GFA immunoreactivity in the cortex graft neuropil was subjectively estimated with fluorescence microscopy. After 3 weeks in oculo, the number of positive structures was significantly lower in the thyroidectomized group as compared to the euthyroid control group. This effect of thyroidectomy on the cortex grafts was entirely counteracted by daily injections of thyroxine (100 μg/kg s.c.) to similarly thyroidectomized recipients. The distribution of GFA-positive structures was even within individual grafts of all three groups. Neither were any differences in morphology of fluorescent astroglial processes observed. The overall density of fluorescent GFA-positive structures was considerably higher than that found in age-matched normal in situ counterparts, even in the thyroidectomized group. After 8 weeks in oculo, the difference between the control and thyroidectomized groups in density of GFA-positive structures in the neuropil had disappeared, and no general increase in density of immunoreactivity was noted in the control group. These results indicate that thyroid hormones might normally play a role for the development of GFA in the early postnatal brain, as thyroid hormone deficiency causes a transient delay in development of GFA immunoreactivity in intraocular cortex cerebri grafts.

Effects of thyroid state on serotonin, 5-hydroxyindoleacetic acid and substance P contents in discrete brain nuclei of adult rats

The effects of chemical thyroidectomy produced by propylthiouracil treatment or hyperthyroidism produced by daily injections of thyroxine on the content of serotonin, its metabolite 5-hydroxyindoleacetic acid and of substance P in discrete brain nuclei of adult rats have been studied. Brain nuclei were removed by punches of frozen brain slices. The serotonin and 5-hydroxyindoleacetic acid contents were measured by high performance liquid chromatography with electrochemical detection while substance P was assayed by radioimmunoassay. The serotonin level was significantly increased in 11 nuclei of the hypothyroid and in 12 nuclei of the hyperthyroid rats. The 5-hydroxyindoleacetic acid levels were higher in 16 nuclei of the hypothyroid and 7 nuclei of the hyperthyroid animals. The state of the thyroid gland in adult rats also affected the substance P system but less consistently than the serotonin pathway. Thus, the substance P content in the brain of propylthiouracil-treated animals increased significantly in 4 nuclei while it decreased in the septum lateralis and the striae terminalis. Following the chronic thyroxine injections, the substance P level was increased in the nucleus caudatus putamen and the tractus diagonalis and was decreased in the area ventralis tegmenti. We previously reported that neonatal thyroidectomy caused a general increase of the substance P and serotonin contents in many brain nuclei of young rats. It appears that the effects of chemical thyroidectomy on mature and immature rat brain are different for the substance P system, suggesting that thyroxine plays an important role in the maturation of substance P-containing neurons.

Toxicity of Leucaena leucocephala in ruminants: the effect of supplemental thyroxine on goats fed on a sole diet of Leucaena

Daily injections of thyroxine were ineffective in overcoming the toxic effects of feeding Leucaena to goats. The treated goats did not differ from the controls in liveweight change or body condition over the 15 weeks of feeding Leucaena and both groups of animals developed oesophageal lesions. Treated animals maintained normal serum thyroxine (T4) and triiodothyronine (T3) levels and did not exhibit the thyroid hyperplasia of the controls. An increase in the serum T4 and T3 levels of three of the control animals after 5 weeks of feeding was associated with declining mimosine concentration in the feed and the ability of the hyperplastic thyroids to produce sufficient T4. Serum analyses suggested zinc deficiency in the control animals, associated with their low thyroid status. It was concluded that the goitrogenicity of 3-hydroxy-4(1H)-pyridone (DHP) is only partly responsible for the toxicity of Leucaena to ruminants, and that the low feed intakes and low liveweight gains are related to other effects of DHP. The evidence for extra-ruminal metabolism of DHP is discussed.

Altered developmental changes of neuromuscular junction in hypo- and hyperthyroid rats.

1. Effects of thyroid hormone on the development of neuromuscular junctions (n.m.j.s.) were investigated electrophysiologically in the diaphragms (sternal region) of normal, hypo- and hyperthyroid rats from the age of birth (day 0) to day 35.2. Hypothyroidism in new-born rats was induced either by daily administration of propylthiouracil to mothers or by subcutaneous injection of 150 muCi (131)I on day 1. Hyperthyroidism was induced by daily injection of thyroxine.3. In normal rats up to day 10, muscle fibres were innervated polyneuronally. By day 20, multiple innervation was eliminated and muscle fibres received only a single input. In hypothyroid rats elimination of polyneuronal innervation was retarded by 5-8 days, while in hyperthyroid rats the elimination was accelerated by 2-3 days.4. The frequency of miniature end-plate potentials (m.e.p.p.s) in normal rats increased from one per 40 sec on days 0-5 to 1/sec on days 25-35. The m.e.p.p. frequency in hypothyroid rats was 25-65% of that in normal rats of the same age. In hyperthyroid rats the m.e.p.p. frequency was normal up to day 18 but subnormal afterwards. The duration of m.e.p.p. measured on day 22-23 was slower in hypothyroid rats and faster in hyperthyroid rats, relative to m.e.p.ps in normal rats.5. The sensitivity to acetylcholine (ACh) at extrajunctional regions in normal rats was about 100 mV/nC at birth and declined to 1 mV/nC by day 26. In hypothyroid rats, the ACh sensitivity was as high as 30 mV/nC on day 26; in hyperthyroid rats, ACh sensitivity on day 26 was undetectable.6. With pairs of nerve stimuli (applied at a 50 msec interval), the second end-plate potential was facilitated until day 10 and depressed after day 16 in normal rats. This shift from facilitation to depression during development was not altered in either hypo-or hyperthyroid rats.7. It is concluded that the lack and excess of thyroid hormone retards and facilitates the development of n.m.j.s. respectively. Possible mechanisms for this altered development are discussed.

Precocious induction of secretory granules by hormones in convoluted tubules of mouse submandibular glands.

Precocious differentiation of convoluted tubules of the submandibular glands of mice was induced by daily injection of thyroxine, insulin, hydrocortisone and 5alpha-dihydrotestosterone from day 4 after birth. This treatment induced enlargement of the tubules and synthesis of secretory granules in the tubules. Treatment with 5alpha-dihydrotestosterone alone had no effect on enlargement of the tubules or synthesis of the granules. These findings suggest that, besides androgenic hormones, these three hormones are also involved in synthesis of granules in developing mice.

Thyroxine-induced calorigenesis in frog liver: Insensitivity to ouabain

Oxygen consumption of liver tissue from leopard frogs ( Rana pipiens complex) given five daily injections of thyroxine (2 μg/l0 g body wt) was 20% higher than the oxygen uptake by liver tissue from control animals. Since inhibition of Na +K + ATPase with ouabain (10 −3 M) had no detectable effect on oxygen consumption of liver tissue from either hyperthyroid or control frogs, it seems that the contribution of active Na + transport to the overall metabolism of liver tissue was too small to be detected by the method of respirometry used in this study. Thus, the thyroxine-induced calorigenesis manifest by liver of leopard frogs cannot be attributed to stimulation of the “sodium pump.”

The effects of propylthiouracil, thyroxine, and hypophysectomy on the iodinating activity of the rat thyroid gland.

The effects of increasing or decreasing the endogenous secretion of thyroid-stimulating hormone on the iodinating activity of the rat thyroid gland were investigated. The thyroid iodinating activity of rats on 0.01% propylthiouracil in the drinking water increased linearly for 3 days and reached a maximum of 230 to 240% of the control on or about the fourth day of treatment. The daily injection of thyroxine (10 μg/100 g intraperitoneally) or hypophysectomy resulted in a rapid decrease in the iodinating activity between the first and second day, approaching a basal level by the third day. When the iodinating activity was suppressed for 4 days by daily injections of thyroxine, the activity began to rise on the fifth day after termination of thyroxine treatment.

Metabolism of 131-I- and 14-C-labeled thyroxines.

Thyroxine metabolism was studied with 4 radiothyroxines labeled as follows: 1) with 131I at 3', 5' positions, 2) with 14C in the beta carbon of the alanine side chain, 3) with 14C in the alanine side chain and ring A, and 4) with 14C in ring B. The study was made in thyroidectomized rats, maintained in a euthyroid state by a daily injection of thyroxine (T4), 15 μg/kg. At the start of an experiment, the replacement therapy was substituted with the injection of a radiothyroxine. Their biological t1, urinary and fecal excretion, and the metabolites in blood, bile, urine and feces of these radiothyroxies were compared. The latter 2 radiothyroxines had t1s of 28.9 and 20.8 hr, while the first 2 radiothyroxines showed similar t1s of 16.6 hr. The total recovery of radioactivity over 10 days was 70- 90% in all experiments, approximately ⅓ of which was recovered in the feces. The urinary recovery varied between groups: more l3lI than 14C was recovered and the least 14C was recovered from the ring B-labeled T4. In...

The influence of thyroxine on the sodium, chloride, and water balance of the toad Bufo bufo

Thyroxine injections have been shown to alter the cutaneous salt balance and urine composition of the starved adult toad Bufo bufo. The net losses of sodium and chloride into the tap water in which the toads were immersed became a net gain after 3 days of thyroxine. This gain was sustained with further daily injections of thyroxine. Urinary volume and total excretion of sodium and chloride were reduced after thyroxine treatment, thus the ion concentrations were decreased. The present in vivo results have been discussed in relation to in vitro effects of thyroxine previously observed on toad bladder and skin. The changes in electrolyte balance during natural moulting, which is controlled in part by thyroxine, are compared to those observed in the present experiments. Weight loss during the first 7 days of thyroxine administration suggests, under the present experimental conditions, a possible metabolic effect of the hormone.

Effect of thyroxine on enzymes of the urea cycle in regenerating rat liver.

SummaryThe activities of carbamyl phosphate synthetase, ornithine transcarbamylase and arginase have been found to be unchanged in regenerating liver of thyroidectomized rats. Complete thyroidectomy results in an impaired rate of liver regeneration. Daily injection of thyroxine during the regeneration period restores the capacity of the liver to regenerate.

Thyroid weight, microscopic structure, and radiodiode concentration at various levels of thyrotrophin secretion in the goitrogen-treated rat.

IN HYPOPHYSECTOMIZED rats, propylthiouracil has been shown to potentiate the response of the thyroid iodide trap to thyrotrophic stimulation (1). The question of whether or not a similar potentiation of this response occurs in intact rats is of importance in interpreting the fact that, in rats with anterior hypothalamic lesions, there is an apparent dichotomy between the metabolic and growth responses of the thyroid gland to goitrogen treatment (2, 3, 4). This question has been examined by Greer (3), who studied thyroid-serum radioiodide concentration (T/S) ratios and thyroid weights in goitrogen treated intact rats (100 gm. in weight) maintained at three different levels of thyrotrophin secretion. Secretion of this hormone was regulated by daily injections of thyroxine, according to the method of Dempsey and Astwood (5) He found that whereas the T/S and thyroid weight were approximately normal in rats given 3.5 or 5.0 μg. doses of racemic thyroxine daily, both were elevated in rats maintained on 2.5 μg./day.